Don't use SkipLocalsInit

Add test and probable fix for Issue 617

.github/workflows/dotnetcore.yml

@@ -12,13 +12,9 @@ jobs:
     - uses: actions/checkout@v1
     - uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 5.0.101
+        dotnet-version: 5.0.401
     - run: dotnet run -p build/build.csproj
     - uses: actions/upload-artifact@v2
       with:
         name: ${{ matrix.os }}-sharpcompress.nupkg
         path: artifacts/*
-    - uses: actions/upload-artifact@v2
-      with:
-        name: ${{ matrix.os }}-sharpcompress.snupkg
-        path: artifacts/*

FORMATS.md

@@ -19,7 +19,6 @@
 | Tar.XZ                 | LZMA2                                             | Decompress          | TarArchive      | TarReader  | TarWriter (3) |
 | GZip (single file)     | DEFLATE                                           | Both                | GZipArchive     | GZipReader | GZipWriter    |
 | 7Zip (4)               | LZMA, LZMA2, BZip2, PPMd, BCJ, BCJ2, Deflate      | Decompress          | SevenZipArchive | N/A        | N/A           |
-| LZip (single file) (5) | LZip (LZMA)                                       | Both                | LZipArchive     | LZipReader | LZipWriter    |
 
 1. SOLID Rars are only supported in the RarReader API.
 2. Zip format supports pkware and WinzipAES encryption. However, encrypted LZMA is not supported. Zip64 reading/writing is supported but only with seekable streams as the Zip spec doesn't support Zip64 data in post data descriptors. Deflate64 is only supported for reading.

build/Program.cs

@@ -49,20 +49,20 @@ class Program
         Target(Build, DependsOn(Format),
                framework =>
                {
-                   if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows) && framework == "net46")
-                   {
-                       return;
-                   }
                    Run("dotnet", "build src/SharpCompress/SharpCompress.csproj -c Release");
                });
 
-        Target(Test, DependsOn(Build), ForEach("net5.0"),
+        Target(Test, DependsOn(Build), ForEach("net5.0", "net461"),
                framework =>
                {
                    IEnumerable<string> GetFiles(string d)
                    {
                        return Glob.Files(".", d);
                    }
+                   if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows) && framework == "net461")
+                   {
+                       return;
+                   }
 
                    foreach (var file in GetFiles("**/*.Test.csproj"))
                    {

build/build.csproj

@@ -6,9 +6,9 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Bullseye" Version="3.6.0" />
+    <PackageReference Include="Bullseye" Version="3.8.0" />
     <PackageReference Include="Glob" Version="1.1.8" />
-    <PackageReference Include="SimpleExec" Version="6.4.0" />
+    <PackageReference Include="SimpleExec" Version="8.0.0" />
   </ItemGroup>
 
 </Project>

global.json

@@ -1,5 +1,6 @@
 {
   "sdk": {
-    "version": "5.0.101"
+    "version": "5.0.300",
+    "rollForward": "latestFeature"
   }
 }

src/SharpCompress/Algorithms/Alder32.cs

@@ -4,7 +4,7 @@
 using System;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
-#if !NETSTANDARD2_0 && !NETSTANDARD2_1
+#if !NETSTANDARD2_0 && !NETSTANDARD2_1 && !NETFRAMEWORK
 using System.Runtime.Intrinsics;
 using System.Runtime.Intrinsics.X86;
 #endif
@@ -22,7 +22,7 @@ namespace SharpCompress.Algorithms
         /// </summary>
         public const uint SeedValue = 1U;
 
-#if !NETSTANDARD2_0 && !NETSTANDARD2_1
+#if !NETSTANDARD2_0 && !NETSTANDARD2_1 && !NETFRAMEWORK
         private const int MinBufferSize = 64;
 #endif
 
@@ -51,12 +51,7 @@ namespace SharpCompress.Algorithms
         /// <returns>The <see cref="uint"/>.</returns>
         public static uint Calculate(uint adler, ReadOnlySpan<byte> buffer)
         {
-            if (buffer.IsEmpty)
-            {
-                return SeedValue;
-            }
-
-#if !NETSTANDARD2_0 && !NETSTANDARD2_1
+#if !NETSTANDARD2_0 && !NETSTANDARD2_1 && !NETFRAMEWORK
             if (Sse3.IsSupported && buffer.Length >= MinBufferSize)
             {
                 return CalculateSse(adler, buffer);
@@ -69,7 +64,7 @@ namespace SharpCompress.Algorithms
         }
 
         // Based on https://github.com/chromium/chromium/blob/master/third_party/zlib/adler32_simd.c
-#if !NETSTANDARD2_0 && !NETSTANDARD2_1
+#if !NETSTANDARD2_0 && !NETSTANDARD2_1 && !NETFRAMEWORK
         private static unsafe uint CalculateSse(uint adler, ReadOnlySpan<byte> buffer)
         {
             uint s1 = adler & 0xFFFF;
@@ -282,4 +277,4 @@ namespace SharpCompress.Algorithms
             return (s2 << 16) | s1;
         }
     }
-}
+}

src/SharpCompress/Archives/GZip/GZipArchive.cs

@@ -98,7 +98,7 @@ namespace SharpCompress.Archives.GZip
         public static bool IsGZipFile(Stream stream)
         {
             // read the header on the first read
-            byte[] header = new byte[10];
+            Span<byte> header = stackalloc byte[10];
 
             // workitem 8501: handle edge case (decompress empty stream)
             if (!stream.ReadFully(header))

src/SharpCompress/Archives/Rar/RarArchive.cs

@@ -10,7 +10,8 @@ using SharpCompress.Readers.Rar;
 
 namespace SharpCompress.Archives.Rar
 {
-    public class RarArchive : AbstractArchive<RarArchiveEntry, RarVolume>
+    public class
+        RarArchive : AbstractArchive<RarArchiveEntry, RarVolume>
     {
         internal Lazy<IRarUnpack> UnpackV2017 { get; } = new Lazy<IRarUnpack>(() => new SharpCompress.Compressors.Rar.UnpackV2017.Unpack());
         internal Lazy<IRarUnpack> UnpackV1 { get; } = new Lazy<IRarUnpack>(() => new SharpCompress.Compressors.Rar.UnpackV1.Unpack());
@@ -42,7 +43,7 @@ namespace SharpCompress.Archives.Rar
 
         protected override IEnumerable<RarArchiveEntry> LoadEntries(IEnumerable<RarVolume> volumes)
         {
-            return RarArchiveEntryFactory.GetEntries(this, volumes);
+            return RarArchiveEntryFactory.GetEntries(this, volumes, ReaderOptions);
         }
 
         protected override IEnumerable<RarVolume> LoadVolumes(IEnumerable<Stream> streams)

src/SharpCompress/Archives/Rar/RarArchiveEntry.cs

@@ -6,6 +6,7 @@ using SharpCompress.Common;
 using SharpCompress.Common.Rar;
 using SharpCompress.Common.Rar.Headers;
 using SharpCompress.Compressors.Rar;
+using SharpCompress.Readers;
 
 namespace SharpCompress.Archives.Rar
 {
@@ -13,11 +14,13 @@ namespace SharpCompress.Archives.Rar
     {
         private readonly ICollection<RarFilePart> parts;
         private readonly RarArchive archive;
+        private readonly ReaderOptions readerOptions;
 
-        internal RarArchiveEntry(RarArchive archive, IEnumerable<RarFilePart> parts)
+        internal RarArchiveEntry(RarArchive archive, IEnumerable<RarFilePart> parts, ReaderOptions readerOptions)
         {
             this.parts = parts.ToList();
             this.archive = archive;
+            this.readerOptions = readerOptions;
         }
 
         public override CompressionType CompressionType => CompressionType.Rar;
@@ -69,13 +72,14 @@ namespace SharpCompress.Archives.Rar
         {
             get
             {
-                return parts.Select(fp => fp.FileHeader).Any(fh => !fh.IsSplitAfter);
+                var headers = parts.Select(x => x.FileHeader);
+                return !headers.First().IsSplitBefore && !headers.Last().IsSplitAfter;
             }
         }
 
         private void CheckIncomplete()
         {
-            if (!IsComplete)
+            if (!readerOptions.DisableCheckIncomplete && !IsComplete)
             {
                 throw new IncompleteArchiveException("ArchiveEntry is incomplete and cannot perform this operation.");
             }

src/SharpCompress/Archives/Rar/RarArchiveEntryFactory.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using SharpCompress.Common.Rar;
+using SharpCompress.Readers;
 
 namespace SharpCompress.Archives.Rar
 {
@@ -36,11 +37,12 @@ namespace SharpCompress.Archives.Rar
         }
 
         internal static IEnumerable<RarArchiveEntry> GetEntries(RarArchive archive,
-                                                                IEnumerable<RarVolume> rarParts)
+                                                                IEnumerable<RarVolume> rarParts,
+                                                                ReaderOptions readerOptions)
         {
             foreach (var groupedParts in GetMatchedFileParts(rarParts))
             {
-                yield return new RarArchiveEntry(archive, groupedParts);
+                yield return new RarArchiveEntry(archive, groupedParts, readerOptions);
             }
         }
     }

src/SharpCompress/AssemblyInfo.cs

@@ -5,7 +5,7 @@ using System.Runtime.CompilerServices;
 [assembly: AssemblyTitle("SharpCompress")]
 [assembly: AssemblyProduct("SharpCompress")]
 [assembly: InternalsVisibleTo("SharpCompress.Test" + SharpCompress.AssemblyInfo.PublicKeySuffix)]
-[assembly: CLSCompliant(true)]
+[assembly: CLSCompliant(false)]
 
 namespace SharpCompress
 {

src/SharpCompress/Common/ArchiveEncoding.cs

@@ -36,7 +36,7 @@ namespace SharpCompress.Common
             Password = password;
         }
 
-#if !NET461
+#if !NETFRAMEWORK
         static ArchiveEncoding()
         {
             Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);

src/SharpCompress/Common/ArchiveType.cs

@@ -6,6 +6,7 @@
         Zip,
         Tar,
         SevenZip,
-        GZip
+        GZip,
+        ZStandard
     }
 }

src/SharpCompress/Common/CompressionType.cs

@@ -14,6 +14,7 @@
         LZip,
         Xz,
         Unknown,
-        Deflate64
+        Deflate64,
+        ZStandard,
     }
 }

src/SharpCompress/Common/ExtractionMethods.cs

@@ -14,14 +14,25 @@ namespace SharpCompress.Common
                                                  Action<string, ExtractionOptions?> write)
         {
             string destinationFileName;
-            string file = Path.GetFileName(entry.Key);
             string fullDestinationDirectoryPath = Path.GetFullPath(destinationDirectory);
 
+            //check for trailing slash.
+            if (fullDestinationDirectoryPath[fullDestinationDirectoryPath.Length - 1] != Path.DirectorySeparatorChar)
+            {
+                fullDestinationDirectoryPath += Path.DirectorySeparatorChar;
+            }
+
+            if (!Directory.Exists(fullDestinationDirectoryPath))
+            {
+                throw new ExtractionException($"Directory does not exist to extract to: {fullDestinationDirectoryPath}");
+            }
+
             options ??= new ExtractionOptions()
             {
                 Overwrite = true
             };
 
+            string file = Path.GetFileName(entry.Key);
             if (options.ExtractFullPath)
             {
                 string folder = Path.GetDirectoryName(entry.Key)!;

src/SharpCompress/Common/GZip/GZipFilePart.cs

@@ -110,13 +110,13 @@ namespace SharpCompress.Common.GZip
 
         private string ReadZeroTerminatedString(Stream stream)
         {
-            byte[] buf1 = new byte[1];
+            Span<byte> buf1 = stackalloc byte[1];
             var list = new List<byte>();
             bool done = false;
             do
             {
                 // workitem 7740
-                int n = stream.Read(buf1, 0, 1);
+                int n = stream.Read(buf1);
                 if (n != 1)
                 {
                     throw new ZlibException("Unexpected EOF reading GZIP header.");

src/SharpCompress/Common/Rar/Headers/FileHeader.cs

@@ -437,6 +437,7 @@ namespace SharpCompress.Common.Rar.Headers
         internal long DataStartPosition { get; set; }
         public Stream PackedStream { get; set; }
 
+        public bool IsSplitBefore => IsRar5 ? HasHeaderFlag(HeaderFlagsV5.SPLIT_BEFORE) : HasFlag(FileFlagsV4.SPLIT_BEFORE);
         public bool IsSplitAfter => IsRar5 ? HasHeaderFlag(HeaderFlagsV5.SPLIT_AFTER) : HasFlag(FileFlagsV4.SPLIT_AFTER);
 
         public bool IsDirectory => HasFlag(IsRar5 ? FileFlagsV5.DIRECTORY : FileFlagsV4.DIRECTORY);

src/SharpCompress/Common/Rar/RarCryptoWrapper.cs

@@ -50,11 +50,11 @@ namespace SharpCompress.Common.Rar
             if (sizeToRead > 0)
             {
                 int alignedSize = sizeToRead + ((~sizeToRead + 1) & 0xf);
-                byte[] cipherText = new byte[RarRijndael.CRYPTO_BLOCK_SIZE];
+                Span<byte> cipherText = stackalloc byte[RarRijndael.CRYPTO_BLOCK_SIZE];
                 for (int i = 0; i < alignedSize / 16; i++)
                 {
                     //long ax = System.currentTimeMillis();
-                    _actualStream.Read(cipherText, 0, RarRijndael.CRYPTO_BLOCK_SIZE);
+                    _actualStream.Read(cipherText);
 
                     var readBytes = _rijndael.ProcessBlock(cipherText);
                     foreach (var readByte in readBytes)

src/SharpCompress/Common/SevenZip/ArchiveReader.cs

@@ -1517,6 +1517,7 @@ namespace SharpCompress.Common.SevenZip
                 }
             }
 
+            byte[] buffer = null;
             foreach (CExtractFolderInfo efi in extractFolderInfoVector)
             {
                 int startIndex;
@@ -1553,7 +1554,7 @@ namespace SharpCompress.Common.SevenZip
 
                 Stream s = DecoderStreamHelper.CreateDecoderStream(_stream, folderStartPackPos, packSizes,
                                                                    folderInfo, db.PasswordProvider);
-                byte[] buffer = new byte[4 << 10];
+                buffer ??= new byte[4 << 10];
                 for (; ; )
                 {
                     int processed = s.Read(buffer, 0, buffer.Length);

src/SharpCompress/Common/SevenZip/SevenZipEntry.cs

@@ -32,7 +32,7 @@ namespace SharpCompress.Common.SevenZip
 
         public override DateTime? ArchivedTime => null;
 
-        public override bool IsEncrypted => false;
+        public override bool IsEncrypted => FilePart.IsEncrypted;
 
         public override bool IsDirectory => FilePart.Header.IsDir;
 

src/SharpCompress/Common/SevenZip/SevenZipFilePart.cs

@@ -102,5 +102,7 @@ namespace SharpCompress.Common.SevenZip
                     throw new NotImplementedException();
             }
         }
+
+        internal bool IsEncrypted => Folder!._coders.FindIndex(c => c._methodId._id == CMethodId.K_AES_ID) != -1;
     }
 }

src/SharpCompress/Common/Tar/Headers/TarHeader.cs

@@ -97,7 +97,7 @@ namespace SharpCompress.Common.Tar.Headers
             {
                 numPaddingBytes = BLOCK_SIZE;
             }
-            output.Write(new byte[numPaddingBytes], 0, numPaddingBytes);
+            output.Write(stackalloc byte[numPaddingBytes]);
         }
 
         internal bool Read(BinaryReader reader)

src/SharpCompress/Common/ZStandard/ZStandardEntry.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using SharpCompress.Common.GZip;
+
+namespace SharpCompress.Common.ZStandard
+{
+    public class ZStandardEntry : Entry
+    {
+        private readonly ZStandardFilePart _filePart;
+
+        internal ZStandardEntry(ZStandardFilePart filePart)
+        {
+            _filePart = filePart;
+        }
+
+        public override CompressionType CompressionType => CompressionType.GZip;
+
+        public override long Crc => _filePart.Crc ?? 0;
+
+        public override string Key => _filePart.FilePartName;
+
+        public override string? LinkTarget => null;
+
+        public override long CompressedSize => 0;
+
+        public override long Size => _filePart.UncompressedSize ?? 0;
+
+        public override DateTime? LastModifiedTime => _filePart.DateModified;
+
+        public override DateTime? CreatedTime => null;
+
+        public override DateTime? LastAccessedTime => null;
+
+        public override DateTime? ArchivedTime => null;
+
+        public override bool IsEncrypted => false;
+
+        public override bool IsDirectory => false;
+
+        public override bool IsSplitAfter => false;
+
+        internal override IEnumerable<FilePart> Parts => _filePart.AsEnumerable<FilePart>();
+
+        internal static IEnumerable<GZipEntry> GetEntries(Stream stream, OptionsBase options)
+        {
+            yield return new GZipEntry(new GZipFilePart(stream, options.ArchiveEncoding));
+        }
+    }
+}

src/SharpCompress/Common/ZStandard/ZStandardFilePart.cs

@@ -0,0 +1,37 @@
+using System;
+using System.IO;
+using ZstdSharp;
+
+namespace SharpCompress.Common.ZStandard
+{
+    internal sealed class ZStandardFilePart : FilePart
+    {
+        private string _name = "";
+        private readonly Stream _stream;
+
+        internal ZStandardFilePart(Stream stream, ArchiveEncoding archiveEncoding)
+            : base(archiveEncoding)
+        {
+            _stream = stream;
+            EntryStartPosition = stream.Position;
+        }
+
+        internal long EntryStartPosition { get; }
+
+        internal DateTime? DateModified { get; private set; }
+        internal int? Crc { get; private set; }
+        internal int? UncompressedSize { get; private set; }
+
+        internal override string FilePartName => _name!;
+
+        internal override Stream GetCompressedStream()
+        {
+            return new DecompressionStream(_stream);
+        }
+
+        internal override Stream GetRawStream()
+        {
+            return _stream;
+        }
+    }
+}

src/SharpCompress/Common/ZStandard/ZStandardVolume.cs

@@ -0,0 +1,23 @@
+using System.IO;
+using SharpCompress.Readers;
+
+namespace SharpCompress.Common.ZStandard
+{
+    public class ZStandardVolume : Volume
+    {
+        public ZStandardVolume(Stream stream, ReaderOptions options)
+            : base(stream, options)
+        {
+        }
+
+        public ZStandardVolume(FileInfo fileInfo, ReaderOptions options)
+            : base(fileInfo.OpenRead(), options)
+        {
+            options.LeaveStreamOpen = false;
+        }
+
+        public override bool IsFirstVolume => true;
+
+        public override bool IsMultiVolume => true;
+    }
+}

src/SharpCompress/Common/Zip/Headers/DirectoryEntryHeader.cs

@@ -63,6 +63,8 @@ namespace SharpCompress.Common.Zip.Headers
             var zip64ExtraData = Extra.OfType<Zip64ExtendedInformationExtraField>().FirstOrDefault();
             if (zip64ExtraData != null)
             {
+                zip64ExtraData.Process(UncompressedSize, CompressedSize, RelativeOffsetOfEntryHeader, DiskNumberStart);
+
                 if (CompressedSize == uint.MaxValue)
                 {
                     CompressedSize = zip64ExtraData.CompressedSize;

src/SharpCompress/Common/Zip/Headers/LocalEntryHeader.cs

@@ -53,6 +53,8 @@ namespace SharpCompress.Common.Zip.Headers
             var zip64ExtraData = Extra.OfType<Zip64ExtendedInformationExtraField>().FirstOrDefault();
             if (zip64ExtraData != null)
             {
+                zip64ExtraData.Process(UncompressedSize, CompressedSize, 0, 0);
+
                 if (CompressedSize == uint.MaxValue)
                 {
                     CompressedSize = zip64ExtraData.CompressedSize;

src/SharpCompress/Common/Zip/Headers/LocalEntryHeaderExtraFactory.cs

@@ -66,62 +66,74 @@ namespace SharpCompress.Common.Zip.Headers
         public Zip64ExtendedInformationExtraField(ExtraDataType type, ushort length, byte[] dataBytes)
             : base(type, length, dataBytes)
         {
-            Process();
         }
 
-        //From the spec values are only in the extradata if the standard
-        //value is set to 0xFFFF, but if one of the sizes are present, both are.
-        //Hence if length == 4 volume only
-        //      if length == 8 offset only
-        //      if length == 12 offset + volume
-        //      if length == 16 sizes only
-        //      if length == 20 sizes + volume
-        //      if length == 24 sizes + offset
-        //      if length == 28 everything.
-        //It is unclear how many of these are used in the wild.
-
-        private void Process()
+        // From the spec, values are only in the extradata if the standard
+        // value is set to 0xFFFFFFFF (or 0xFFFF for the Disk Start Number).
+        // Values, if present, must appear in the following order:
+        // - Original Size
+        // - Compressed Size
+        // - Relative Header Offset
+        // - Disk Start Number
+        public void Process(long uncompressedFileSize, long compressedFileSize, long relativeHeaderOffset, ushort diskNumber)
         {
-            switch (DataBytes.Length)
+            var bytesRequired = ((uncompressedFileSize == uint.MaxValue) ? 8 : 0)
+                + ((compressedFileSize == uint.MaxValue) ? 8 : 0)
+                + ((relativeHeaderOffset == uint.MaxValue) ? 8 : 0)
+                + ((diskNumber == ushort.MaxValue) ? 4 : 0);
+            var currentIndex = 0;
+
+            if (bytesRequired > DataBytes.Length)
             {
-                case 4:
-                    VolumeNumber = BinaryPrimitives.ReadUInt32LittleEndian(DataBytes);
-                    return;
-                case 8:
-                    RelativeOffsetOfEntryHeader = BinaryPrimitives.ReadInt64LittleEndian(DataBytes);
-                    return;
-                case 12:
-                    RelativeOffsetOfEntryHeader = BinaryPrimitives.ReadInt64LittleEndian(DataBytes);
-                    VolumeNumber = BinaryPrimitives.ReadUInt32LittleEndian(DataBytes.AsSpan(8));
-                    return;
-                case 16:
-                    UncompressedSize = BinaryPrimitives.ReadInt64LittleEndian(DataBytes);
-                    CompressedSize = BinaryPrimitives.ReadInt64LittleEndian(DataBytes.AsSpan(8));
-                    return;
-                case 20:
-                    UncompressedSize = BinaryPrimitives.ReadInt64LittleEndian(DataBytes);
-                    CompressedSize = BinaryPrimitives.ReadInt64LittleEndian(DataBytes.AsSpan(8));
-                    VolumeNumber = BinaryPrimitives.ReadUInt32LittleEndian(DataBytes.AsSpan(16));
-                    return;
-                case 24:
-                    UncompressedSize = BinaryPrimitives.ReadInt64LittleEndian(DataBytes);
-                    CompressedSize = BinaryPrimitives.ReadInt64LittleEndian(DataBytes.AsSpan(8));
-                    RelativeOffsetOfEntryHeader = BinaryPrimitives.ReadInt64LittleEndian(DataBytes.AsSpan(16));
-                    return;
-                case 28:
-                    UncompressedSize = BinaryPrimitives.ReadInt64LittleEndian(DataBytes);
-                    CompressedSize = BinaryPrimitives.ReadInt64LittleEndian(DataBytes.AsSpan(8));
-                    RelativeOffsetOfEntryHeader = BinaryPrimitives.ReadInt64LittleEndian(DataBytes.AsSpan(16));
-                    VolumeNumber = BinaryPrimitives.ReadUInt32LittleEndian(DataBytes.AsSpan(24));
-                    return;
-                default:
-                    throw new ArchiveException("Unexpected size of of Zip64 extended information extra field");
+                throw new ArchiveException("Zip64 extended information extra field is not large enough for the required information");
+            }
+
+            if (uncompressedFileSize == uint.MaxValue)
+            {
+                UncompressedSize = BinaryPrimitives.ReadInt64LittleEndian(DataBytes.AsSpan(currentIndex));
+                currentIndex += 8;
+            }
+
+            if (compressedFileSize == uint.MaxValue)
+            {
+                CompressedSize = BinaryPrimitives.ReadInt64LittleEndian(DataBytes.AsSpan(currentIndex));
+                currentIndex += 8;
+            }
+
+            if (relativeHeaderOffset == uint.MaxValue)
+            {
+                RelativeOffsetOfEntryHeader = BinaryPrimitives.ReadInt64LittleEndian(DataBytes.AsSpan(currentIndex));
+                currentIndex += 8;
+            }
+
+            if (diskNumber == ushort.MaxValue)
+            {
+                VolumeNumber = BinaryPrimitives.ReadUInt32LittleEndian(DataBytes.AsSpan(currentIndex));
             }
         }
 
+        /// <summary>
+        /// Uncompressed file size. Only valid after <see cref="Process(long, long, long, ushort)"/> has been called and if the
+        /// original entry header had a corresponding 0xFFFFFFFF value.
+        /// </summary>
         public long UncompressedSize { get; private set; }
+
+        /// <summary>
+        /// Compressed file size. Only valid after <see cref="Process(long, long, long, ushort)"/> has been called and if the
+        /// original entry header had a corresponding 0xFFFFFFFF value.
+        /// </summary>
         public long CompressedSize { get; private set; }
+
+        /// <summary>
+        /// Relative offset of the entry header. Only valid after <see cref="Process(long, long, long, ushort)"/> has been called and if the
+        /// original entry header had a corresponding 0xFFFFFFFF value.
+        /// </summary>
         public long RelativeOffsetOfEntryHeader { get; private set; }
+
+        /// <summary>
+        /// Volume number. Only valid after <see cref="Process(long, long, long, ushort)"/> has been called and if the
+        /// original entry header had a corresponding 0xFFFF value.
+        /// </summary>
         public uint VolumeNumber { get; private set; }
     }
 

src/SharpCompress/Common/Zip/Headers/ZipFileEntry.cs

@@ -105,6 +105,6 @@ namespace SharpCompress.Common.Zip.Headers
 
         internal ZipFilePart Part { get; set; }
 
-        internal bool IsZip64 => CompressedSize == uint.MaxValue;
+        internal bool IsZip64 => CompressedSize >= uint.MaxValue;
     }
 }

src/SharpCompress/Common/Zip/SeekableZipHeaderFactory.cs

@@ -8,7 +8,10 @@ namespace SharpCompress.Common.Zip
 {
     internal sealed class SeekableZipHeaderFactory : ZipHeaderFactory
     {
-        private const int MAX_ITERATIONS_FOR_DIRECTORY_HEADER = 4096;
+        private const int MINIMUM_EOCD_LENGTH = 22;
+        private const int ZIP64_EOCD_LENGTH = 20;
+        // Comment may be within 64kb + structure 22 bytes
+        private const int MAX_SEARCH_LENGTH_FOR_EOCD = 65557;
         private bool _zip64;
 
         internal SeekableZipHeaderFactory(string? password, ArchiveEncoding archiveEncoding)
@@ -20,14 +23,24 @@ namespace SharpCompress.Common.Zip
         {
             var reader = new BinaryReader(stream);
 
-            SeekBackToHeader(stream, reader, DIRECTORY_END_HEADER_BYTES);
+            SeekBackToHeader(stream, reader);
+
+            var eocd_location = stream.Position;
             var entry = new DirectoryEndHeader();
             entry.Read(reader);
 
             if (entry.IsZip64)
             {
                 _zip64 = true;
-                SeekBackToHeader(stream, reader, ZIP64_END_OF_CENTRAL_DIRECTORY_LOCATOR);
+
+                // ZIP64_END_OF_CENTRAL_DIRECTORY_LOCATOR should be before the EOCD
+                stream.Seek(eocd_location - ZIP64_EOCD_LENGTH - 4, SeekOrigin.Begin);
+                uint zip64_locator = reader.ReadUInt32();
+                if (zip64_locator != ZIP64_END_OF_CENTRAL_DIRECTORY_LOCATOR)
+                {
+                    throw new ArchiveException("Failed to locate the Zip64 Directory Locator");
+                }
+
                 var zip64Locator = new Zip64DirectoryEndLocatorHeader();
                 zip64Locator.Read(reader);
 
@@ -73,27 +86,50 @@ namespace SharpCompress.Common.Zip
             }
         }
 
-        private static void SeekBackToHeader(Stream stream, BinaryReader reader, uint headerSignature)
+        private static bool IsMatch(byte[] haystack, int position, byte[] needle)
         {
-            long offset = 0;
-            uint signature;
-            int iterationCount = 0;
-            do
+            for (int i = 0; i < needle.Length; i++)
             {
-                if ((stream.Length + offset) - 4 < 0)
+                if (haystack[position + i] != needle[i])
                 {
-                    throw new ArchiveException("Failed to locate the Zip Header");
-                }
-                stream.Seek(offset - 4, SeekOrigin.End);
-                signature = reader.ReadUInt32();
-                offset--;
-                iterationCount++;
-                if (iterationCount > MAX_ITERATIONS_FOR_DIRECTORY_HEADER)
-                {
-                    throw new ArchiveException("Could not find Zip file Directory at the end of the file.  File may be corrupted.");
+                    return false;
                 }
             }
-            while (signature != headerSignature);
+
+            return true;
+        }
+        private static void SeekBackToHeader(Stream stream, BinaryReader reader)
+        {
+            // Minimum EOCD length
+            if (stream.Length < MINIMUM_EOCD_LENGTH)
+            {
+                throw new ArchiveException("Could not find Zip file Directory at the end of the file. File may be corrupted.");
+            }
+
+            int len = stream.Length < MAX_SEARCH_LENGTH_FOR_EOCD ? (int)stream.Length : MAX_SEARCH_LENGTH_FOR_EOCD;
+            // We search for marker in reverse to find the first occurance
+            byte[] needle = { 0x06, 0x05, 0x4b, 0x50 };
+
+            stream.Seek(-len, SeekOrigin.End);
+
+            byte[] seek = reader.ReadBytes(len);
+
+            // Search in reverse
+            Array.Reverse(seek);
+
+            // don't exclude the minimum eocd region, otherwise you fail to locate the header in empty zip files
+            var max_search_area = len; // - MINIMUM_EOCD_LENGTH;
+
+            for (int pos_from_end = 0; pos_from_end < max_search_area; ++pos_from_end)
+            {
+                if (IsMatch(seek, pos_from_end, needle))
+                {
+                    stream.Seek(-pos_from_end, SeekOrigin.End);
+                    return;
+                }
+            }
+
+            throw new ArchiveException("Failed to locate the Zip Header");
         }
 
         internal LocalEntryHeader GetLocalHeader(Stream stream, DirectoryEntryHeader directoryEntryHeader)

src/SharpCompress/Common/Zip/WinzipAesCryptoStream.cs

@@ -75,7 +75,7 @@ namespace SharpCompress.Common.Zip
             if (disposing)
             {
                 //read out last 10 auth bytes
-                var ten = new byte[10];
+                Span<byte> ten = stackalloc byte[10];
                 _stream.ReadFully(ten);
                 _stream.Dispose();
             }

src/SharpCompress/Common/Zip/ZipFilePart.cs

@@ -93,7 +93,7 @@ namespace SharpCompress.Common.Zip
                     }
                 case ZipCompressionMethod.PPMd:
                     {
-                        var props = new byte[2];
+                        Span<byte> props = stackalloc byte[2];
                         stream.ReadFully(props);
                         return new PpmdStream(new PpmdProperties(props), stream, false);
                     }

src/SharpCompress/Compressors/BZip2/BZip2Stream.cs

@@ -83,7 +83,7 @@ namespace SharpCompress.Compressors.BZip2
             stream.SetLength(value);
         }
 
-#if !NET461 && !NETSTANDARD2_0
+#if !NETFRAMEWORK && !NETSTANDARD2_0
 
         public override int Read(Span<byte> buffer)
         {
@@ -123,4 +123,4 @@ namespace SharpCompress.Compressors.BZip2
             return true;
         }
     }
-}
+}

src/SharpCompress/Compressors/Deflate/ZlibBaseStream.cs

@@ -256,17 +256,15 @@ namespace SharpCompress.Compressors.Deflate
                         }
 
                         // Read and potentially verify the GZIP trailer: CRC32 and  size mod 2^32
-                        byte[] trailer = new byte[8];
+                        Span<byte> trailer = stackalloc byte[8];
 
                         // workitem 8679
                         if (_z.AvailableBytesIn != 8)
                         {
                             // Make sure we have read to the end of the stream
-                            Array.Copy(_z.InputBuffer, _z.NextIn, trailer, 0, _z.AvailableBytesIn);
+                            _z.InputBuffer.AsSpan(_z.NextIn, _z.AvailableBytesIn).CopyTo(trailer);
                             int bytesNeeded = 8 - _z.AvailableBytesIn;
-                            int bytesRead = _stream.Read(trailer,
-                                                         _z.AvailableBytesIn,
-                                                         bytesNeeded);
+                            int bytesRead = _stream.Read(trailer.Slice(_z.AvailableBytesIn, bytesNeeded));
                             if (bytesNeeded != bytesRead)
                             {
                                 throw new ZlibException(String.Format(
@@ -276,12 +274,12 @@ namespace SharpCompress.Compressors.Deflate
                         }
                         else
                         {
-                            Array.Copy(_z.InputBuffer, _z.NextIn, trailer, 0, trailer.Length);
+                            _z.InputBuffer.AsSpan(_z.NextIn, trailer.Length).CopyTo(trailer);
                         }
 
                         Int32 crc32_expected = BinaryPrimitives.ReadInt32LittleEndian(trailer);
                         Int32 crc32_actual = crc.Crc32Result;
-                        Int32 isize_expected = BinaryPrimitives.ReadInt32LittleEndian(trailer.AsSpan(4));
+                        Int32 isize_expected = BinaryPrimitives.ReadInt32LittleEndian(trailer.Slice(4));
                         Int32 isize_actual = (Int32)(_z.TotalBytesOut & 0x00000000FFFFFFFF);
 
                         if (crc32_actual != crc32_expected)
@@ -504,13 +502,37 @@ namespace SharpCompress.Compressors.Deflate
                 throw new ZlibException("Cannot Read after Writing.");
             }
 
+            int rc = 0;
+
+            // set up the output of the deflate/inflate codec:
+            _z.OutputBuffer = buffer;
+            _z.NextOut = offset;
+            _z.AvailableBytesOut = count;
+
             if (count == 0)
             {
                 return 0;
             }
             if (nomoreinput && _wantCompress)
             {
-                return 0; // workitem 8557
+                // no more input data available; therefore we flush to
+                // try to complete the read
+                rc = _z.Deflate(FlushType.Finish);
+
+                if (rc != ZlibConstants.Z_OK && rc != ZlibConstants.Z_STREAM_END)
+                {
+                    throw new ZlibException(String.Format("Deflating:  rc={0}  msg={1}", rc, _z.Message));
+                }
+
+                rc = (count - _z.AvailableBytesOut);
+
+                // calculate CRC after reading
+                if (crc != null)
+                {
+                    crc.SlurpBlock(buffer, offset, rc);
+                }
+
+                return rc;
             }
             if (buffer is null)
             {
@@ -529,13 +551,6 @@ namespace SharpCompress.Compressors.Deflate
                 throw new ArgumentOutOfRangeException(nameof(count));
             }
 
-            int rc = 0;
-
-            // set up the output of the deflate/inflate codec:
-            _z.OutputBuffer = buffer;
-            _z.NextOut = offset;
-            _z.AvailableBytesOut = count;
-
             // This is necessary in case _workingBuffer has been resized. (new byte[])
             // (The first reference to _workingBuffer goes through the private accessor which
             // may initialize it.)

src/SharpCompress/Compressors/LZMA/LZipStream.cs

@@ -59,16 +59,16 @@ namespace SharpCompress.Compressors.LZMA
                     crc32Stream.Dispose();
                     var compressedCount = _countingWritableSubStream!.Count;
 
-                    byte[] intBuf = new byte[8];
+                    Span<byte> intBuf = stackalloc byte[8];
                     BinaryPrimitives.WriteUInt32LittleEndian(intBuf, crc32Stream.Crc);
-                    _countingWritableSubStream.Write(intBuf, 0, 4);
+                    _countingWritableSubStream.Write(intBuf.Slice(0, 4));
 
                     BinaryPrimitives.WriteInt64LittleEndian(intBuf, _writeCount);
-                    _countingWritableSubStream.Write(intBuf, 0, 8);
+                    _countingWritableSubStream.Write(intBuf);
 
                     //total with headers
                     BinaryPrimitives.WriteUInt64LittleEndian(intBuf, compressedCount + 6 + 20);
-                    _countingWritableSubStream.Write(intBuf, 0, 8);
+                    _countingWritableSubStream.Write(intBuf);
                 }
                 _finished = true;
             }
@@ -118,7 +118,7 @@ namespace SharpCompress.Compressors.LZMA
         public override void SetLength(long value) => throw new NotImplementedException();
 
 
-#if !NET461 && !NETSTANDARD2_0
+#if !NETFRAMEWORK && !NETSTANDARD2_0
 
         public override int Read(Span<byte> buffer)
         {

src/SharpCompress/Compressors/PPMd/PpmdProperties.cs

@@ -31,7 +31,11 @@ namespace SharpCompress.Compressors.PPMd
         public PpmdVersion Version { get; } = PpmdVersion.I1;
         internal ModelRestorationMethod RestorationMethod { get; }
 
-        public PpmdProperties(byte[] properties)
+        public PpmdProperties(byte[] properties) : this(properties.AsSpan())
+        {
+        }
+
+        public PpmdProperties(ReadOnlySpan<byte> properties)
         {
             if (properties.Length == 2)
             {
@@ -43,7 +47,7 @@ namespace SharpCompress.Compressors.PPMd
             else if (properties.Length == 5)
             {
                 Version = PpmdVersion.H7Z;
-                AllocatorSize = BinaryPrimitives.ReadInt32LittleEndian(properties.AsSpan(1));
+                AllocatorSize = BinaryPrimitives.ReadInt32LittleEndian(properties.Slice(1));
                 ModelOrder = properties[0];
             }
         }

src/SharpCompress/Compressors/Xz/BinaryUtils.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Buffers.Binary;
 using System.IO;
 
 namespace SharpCompress.Compressors.Xz
@@ -8,7 +9,7 @@ namespace SharpCompress.Compressors.Xz
         public static int ReadLittleEndianInt32(this BinaryReader reader)
         {
             byte[] bytes = reader.ReadBytes(4);
-            return (bytes[0] + (bytes[1] << 8) + (bytes[2] << 16) + (bytes[3] << 24));
+            return BinaryPrimitives.ReadInt32LittleEndian(bytes);
         }
 
         internal static uint ReadLittleEndianUInt32(this BinaryReader reader)
@@ -17,13 +18,13 @@ namespace SharpCompress.Compressors.Xz
         }
         public static int ReadLittleEndianInt32(this Stream stream)
         {
-            byte[] bytes = new byte[4];
+            Span<byte> bytes = stackalloc byte[4];
             var read = stream.ReadFully(bytes);
             if (!read)
             {
                 throw new EndOfStreamException();
             }
-            return (bytes[0] + (bytes[1] << 8) + (bytes[2] << 16) + (bytes[3] << 24));
+            return BinaryPrimitives.ReadInt32LittleEndian(bytes);
         }
 
         internal static uint ReadLittleEndianUInt32(this Stream stream)

src/SharpCompress/Compressors/Xz/Crc32.cs

@@ -1,7 +1,6 @@
 #nullable disable
 
 using System;
-using System.Collections.Generic;
 
 namespace SharpCompress.Compressors.Xz
 {
@@ -24,7 +23,7 @@ namespace SharpCompress.Compressors.Xz
 
         public static UInt32 Compute(UInt32 polynomial, UInt32 seed, byte[] buffer)
         {
-            return ~CalculateHash(InitializeTable(polynomial), seed, buffer, 0, buffer.Length);
+            return ~CalculateHash(InitializeTable(polynomial), seed, buffer);
         }
 
         private static UInt32[] InitializeTable(UInt32 polynomial)
@@ -61,16 +60,16 @@ namespace SharpCompress.Compressors.Xz
             return createTable;
         }
 
-        private static UInt32 CalculateHash(UInt32[] table, UInt32 seed, IList<byte> buffer, int start, int size)
+        private static UInt32 CalculateHash(UInt32[] table, UInt32 seed, ReadOnlySpan<byte> buffer)
         {
             var crc = seed;
-            for (var i = start; i < size - start; i++)
+            int len = buffer.Length;
+            for (var i = 0; i < len; i++)
             {
-                crc = (crc >> 8) ^ table[buffer[i] ^ crc & 0xff];
+                crc = (crc >> 8) ^ table[(buffer[i] ^ crc) & 0xff];
             }
 
             return crc;
         }
-
     }
 }

src/SharpCompress/Compressors/Xz/Crc64.cs

@@ -22,14 +22,14 @@ namespace SharpCompress.Compressors.Xz
         {
             Table ??= CreateTable(Iso3309Polynomial);
 
-            return CalculateHash(seed, Table, buffer, 0, buffer.Length);
+            return CalculateHash(seed, Table, buffer);
         }
 
-        public static UInt64 CalculateHash(UInt64 seed, UInt64[] table, IList<byte> buffer, int start, int size)
+        public static UInt64 CalculateHash(UInt64 seed, UInt64[] table, ReadOnlySpan<byte> buffer)
         {
             var crc = seed;
-
-            for (var i = start; i < size; i++)
+            int len = buffer.Length;
+            for (var i = 0; i < len; i++)
             {
                 unchecked
                 {

src/SharpCompress/Compressors/Zstd/CompressionStream.cs

@@ -0,0 +1,201 @@
+using System;
+using System.Buffers;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using ZstdSharp.Unsafe;
+
+namespace ZstdSharp
+{
+    public class CompressionStream : Stream
+    {
+        private readonly Stream innerStream;
+        private readonly byte[] outputBuffer;
+        private Compressor compressor;
+        private ZSTD_outBuffer_s output;
+
+        public CompressionStream(Stream stream, int level = Compressor.DefaultCompressionLevel,
+            int bufferSize = 0)
+        {
+            if (stream == null)
+                throw new ArgumentNullException(nameof(stream));
+
+            if (!stream.CanWrite)
+                throw new ArgumentException("Stream is not writable", nameof(stream));
+
+            if (bufferSize < 0)
+                throw new ArgumentOutOfRangeException(nameof(bufferSize));
+
+            innerStream = stream;
+            compressor = new Compressor(level);
+
+            var outputBufferSize =
+                bufferSize > 0 ? bufferSize : (int) Methods.ZSTD_CStreamOutSize().EnsureZstdSuccess();
+            outputBuffer = ArrayPool<byte>.Shared.Rent(outputBufferSize);
+            output = new ZSTD_outBuffer_s {pos = 0, size = (nuint) outputBufferSize};
+        }
+
+        public void SetParameter(ZSTD_cParameter parameter, int value)
+        {
+            EnsureNotDisposed();
+            compressor.SetParameter(parameter, value);
+        }
+
+        public int GetParameter(ZSTD_cParameter parameter)
+        {
+            EnsureNotDisposed();
+            return compressor.GetParameter(parameter);
+        }
+
+        public void LoadDictionary(byte[] dict)
+        {
+            EnsureNotDisposed();
+            compressor.LoadDictionary(dict);
+        }
+
+        ~CompressionStream() => Dispose(false);
+
+#if !NETSTANDARD2_0 && !NET461
+        public override async ValueTask DisposeAsync()
+#else
+        public async ValueTask DisposeAsync()
+#endif
+        {
+            if (compressor == null)
+                return;
+
+            try
+            {
+                await FlushAsync().ConfigureAwait(false);
+            }
+            finally
+            {
+                ReleaseUnmanagedResources();
+                GC.SuppressFinalize(this);
+            }
+        }
+
+        protected override void Dispose(bool disposing)
+        {
+            if (compressor == null)
+                return;
+
+            try
+            {
+                if (disposing)
+                    Flush();
+            }
+            finally
+            {
+                ReleaseUnmanagedResources();
+            }
+        }
+
+        private void ReleaseUnmanagedResources()
+        {
+            compressor.Dispose();
+            ArrayPool<byte>.Shared.Return(outputBuffer);
+        }
+
+        public override void Flush() 
+            => WriteInternal(null, true);
+
+        public override async Task FlushAsync(CancellationToken cancellationToken)
+            => await WriteInternalAsync(null, true, cancellationToken).ConfigureAwait(false);
+
+        public override void Write(byte[] buffer, int offset, int count)
+            => Write(new ReadOnlySpan<byte>(buffer, offset, count));
+
+#if !NETSTANDARD2_0 && !NET461
+        public override void Write(ReadOnlySpan<byte> buffer)
+            => WriteInternal(buffer, false);
+#else
+        public void Write(ReadOnlySpan<byte> buffer)
+            => WriteInternal(buffer, false);
+#endif
+
+        private void WriteInternal(ReadOnlySpan<byte> buffer, bool lastChunk)
+        {
+            EnsureNotDisposed();
+
+            var input = new ZSTD_inBuffer_s {pos = 0, size = buffer != null ? (nuint) buffer.Length : 0};
+            nuint remaining;
+            do
+            {
+                output.pos = 0;
+                remaining = CompressStream(ref input, buffer,
+                    lastChunk ? ZSTD_EndDirective.ZSTD_e_end : ZSTD_EndDirective.ZSTD_e_continue);
+
+                var written = (int) output.pos;
+                if (written > 0)
+                    innerStream.Write(outputBuffer, 0, written);
+            } while (lastChunk ? remaining > 0 : input.pos < input.size);
+        }
+
+        private async ValueTask WriteInternalAsync(ReadOnlyMemory<byte>? buffer, bool lastChunk,
+            CancellationToken cancellationToken = default)
+        {
+            EnsureNotDisposed();
+
+            var input = new ZSTD_inBuffer_s { pos = 0, size = buffer.HasValue ? (nuint)buffer.Value.Length : 0 };
+            nuint remaining;
+            do
+            {
+                output.pos = 0;
+                remaining = CompressStream(ref input, buffer.HasValue ? buffer.Value.Span : null,
+                    lastChunk ? ZSTD_EndDirective.ZSTD_e_end : ZSTD_EndDirective.ZSTD_e_continue);
+
+                var written = (int) output.pos;
+                if (written > 0)
+                    await innerStream.WriteAsync(outputBuffer, 0, written, cancellationToken).ConfigureAwait(false);
+            } while (lastChunk ? remaining > 0 : input.pos < input.size);
+        }
+
+        public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+            => WriteAsync(new ReadOnlyMemory<byte>(buffer, offset, count), cancellationToken).AsTask();
+
+#if !NETSTANDARD2_0 && !NET461
+        public override async ValueTask WriteAsync(ReadOnlyMemory<byte> buffer,
+            CancellationToken cancellationToken = default)
+            => await WriteInternalAsync(buffer, false, cancellationToken).ConfigureAwait(false);
+#else
+        public async ValueTask WriteAsync(ReadOnlyMemory<byte> buffer,
+            CancellationToken cancellationToken = default)
+            => await WriteInternalAsync(buffer, false, cancellationToken).ConfigureAwait(false);
+#endif
+
+        internal unsafe nuint CompressStream(ref ZSTD_inBuffer_s input, ReadOnlySpan<byte> inputBuffer,
+            ZSTD_EndDirective directive)
+        {
+            fixed (byte* inputBufferPtr = inputBuffer)
+            fixed (byte* outputBufferPtr = outputBuffer)
+            {
+                input.src = inputBufferPtr;
+                output.dst = outputBufferPtr;
+                return compressor.CompressStream(ref input, ref output, directive).EnsureZstdSuccess();
+            }
+        }
+
+        public override bool CanRead => false;
+        public override bool CanSeek => false;
+        public override bool CanWrite => true;
+
+        public override long Length => throw new NotSupportedException();
+
+        public override long Position
+        {
+            get => throw new NotSupportedException();
+            set => throw new NotSupportedException();
+        }
+
+        public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
+        public override void SetLength(long value) => throw new NotSupportedException();
+        public override int Read(byte[] buffer, int offset, int count) => throw new NotSupportedException();
+
+        private void EnsureNotDisposed()
+        {
+            if (compressor == null)
+                throw new ObjectDisposedException(nameof(CompressionStream));
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Compressor.cs

@@ -0,0 +1,164 @@
+using System;
+using ZstdSharp.Unsafe;
+
+namespace ZstdSharp
+{
+    public unsafe class Compressor : IDisposable
+    {
+        public static int MinCompressionLevel => Methods.ZSTD_minCLevel();
+        public static int MaxCompressionLevel => Methods.ZSTD_maxCLevel();
+        public const int DefaultCompressionLevel = 0;
+
+        private int level = DefaultCompressionLevel;
+
+        private ZSTD_CCtx_s* cctx;
+
+        public int Level
+        {
+            get => level;
+            set
+            {
+                if (level != value)
+                {
+                    level = value;
+                    SetParameter(ZSTD_cParameter.ZSTD_c_compressionLevel, value);
+                }
+            }
+        }
+
+        public void SetParameter(ZSTD_cParameter parameter, int value)
+        {
+            EnsureNotDisposed();
+            Methods.ZSTD_CCtx_setParameter(cctx, parameter, value).EnsureZstdSuccess();
+        }
+
+        public int GetParameter(ZSTD_cParameter parameter)
+        {
+            EnsureNotDisposed();
+            int value;
+            Methods.ZSTD_CCtx_getParameter(cctx, parameter, &value).EnsureZstdSuccess();
+            return value;
+        }
+
+        public void LoadDictionary(byte[] dict)
+        {
+            EnsureNotDisposed();
+            if (dict == null)
+            {
+                Methods.ZSTD_CCtx_loadDictionary(cctx, null, 0).EnsureZstdSuccess();
+            }
+            else
+            {
+
+                fixed (byte* dictPtr = dict)
+                    Methods.ZSTD_CCtx_loadDictionary(cctx, dictPtr, (nuint) dict.Length).EnsureZstdSuccess();
+            }
+        }
+
+        public Compressor(int level = DefaultCompressionLevel)
+        {
+            cctx = Methods.ZSTD_createCCtx();
+            if (cctx == null)
+                throw new ZstdException(ZSTD_ErrorCode.ZSTD_error_GENERIC, "Failed to create cctx");
+
+            Level = level;
+        }
+
+        ~Compressor()
+        {
+            ReleaseUnmanagedResources();
+        }
+
+        public static int GetCompressBound(int length) 
+            => (int) Methods.ZSTD_compressBound((nuint) length);
+
+        public static ulong GetCompressBoundLong(ulong length)
+            => Methods.ZSTD_compressBound((nuint) length);
+
+        public Span<byte> Wrap(ReadOnlySpan<byte> src)
+        {
+            var dest = new byte[GetCompressBound(src.Length)];
+            var length = Wrap(src, dest);
+            return new Span<byte>(dest, 0, length);
+        }
+
+        public int Wrap(byte[] src, byte[] dest, int offset)
+            => Wrap(src, new Span<byte>(dest, offset, dest.Length - offset));
+
+        public int Wrap(ReadOnlySpan<byte> src, Span<byte> dest)
+        {
+            EnsureNotDisposed();
+            fixed (byte* srcPtr = src)
+            fixed (byte* destPtr = dest)
+                return (int) Methods
+                    .ZSTD_compress2(cctx, destPtr, (nuint) dest.Length, srcPtr, (nuint) src.Length)
+                    .EnsureZstdSuccess();
+        }
+
+        public int Wrap(ArraySegment<byte> src, ArraySegment<byte> dest) 
+            => Wrap((ReadOnlySpan<byte>) src, dest);
+
+        public int Wrap(byte[] src, int srcOffset, int srcLength, byte[] dst, int dstOffset, int dstLength) 
+            => Wrap(new ReadOnlySpan<byte>(src, srcOffset, srcLength), new Span<byte>(dst, dstOffset, dstLength));
+
+        public bool TryWrap(byte[] src, byte[] dest, int offset, out int written)
+            => TryWrap(src, new Span<byte>(dest, offset, dest.Length - offset), out written);
+
+        public bool TryWrap(ReadOnlySpan<byte> src, Span<byte> dest, out int written)
+        {
+            EnsureNotDisposed();
+            fixed (byte* srcPtr = src)
+            fixed (byte* destPtr = dest)
+            {
+                var returnValue =
+                    Methods.ZSTD_compress2(cctx, destPtr, (nuint) dest.Length, srcPtr, (nuint) src.Length);
+
+                if (returnValue == unchecked(0 - (nuint)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall))
+                {
+                    written = default;
+                    return false;
+                }
+
+                returnValue.EnsureZstdSuccess();
+                written = (int) returnValue;
+                return true;
+            }
+        }
+
+        public bool TryWrap(ArraySegment<byte> src, ArraySegment<byte> dest, out int written)
+            => TryWrap((ReadOnlySpan<byte>)src, dest, out written);
+
+        public bool TryWrap(byte[] src, int srcOffset, int srcLength, byte[] dst, int dstOffset, int dstLength, out int written)
+            => TryWrap(new ReadOnlySpan<byte>(src, srcOffset, srcLength), new Span<byte>(dst, dstOffset, dstLength), out written);
+
+        private void ReleaseUnmanagedResources()
+        {
+            if (cctx != null)
+            {
+                Methods.ZSTD_freeCCtx(cctx);
+                cctx = null;
+            }
+        }
+
+        public void Dispose()
+        {
+            ReleaseUnmanagedResources();
+            GC.SuppressFinalize(this);
+        }
+
+        private void EnsureNotDisposed()
+        {
+            if (cctx == null)
+                throw new ObjectDisposedException(nameof(Compressor));
+        }
+
+        internal nuint CompressStream(ref ZSTD_inBuffer_s input, ref ZSTD_outBuffer_s output, ZSTD_EndDirective directive)
+        {
+            fixed (ZSTD_inBuffer_s* inputPtr = &input)
+            fixed (ZSTD_outBuffer_s* outputPtr = &output)
+            {
+                return Methods.ZSTD_compressStream2(cctx, outputPtr, inputPtr, directive).EnsureZstdSuccess();
+            }
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Constants.cs

@@ -0,0 +1,9 @@
+namespace ZstdSharp
+{
+	internal class Constants
+	{
+		//NOTE: https://docs.microsoft.com/en-us/dotnet/framework/configure-apps/file-schema/runtime/gcallowverylargeobjects-element#remarks
+		//NOTE: https://github.com/dotnet/runtime/blob/v5.0.0-rtm.20519.4/src/libraries/System.Private.CoreLib/src/System/Array.cs#L27
+		public const ulong MaxByteArrayLength = 0x7FFFFFC7;
+	}
+}

src/SharpCompress/Compressors/Zstd/DecompressionStream.cs

@@ -0,0 +1,190 @@
+using System;
+using System.Buffers;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using ZstdSharp.Unsafe;
+
+namespace ZstdSharp
+{
+    public class DecompressionStream : Stream
+    {
+        private readonly Stream innerStream;
+        private readonly byte[] inputBuffer;
+        private readonly int inputBufferSize;
+        private Decompressor decompressor;
+        private ZSTD_inBuffer_s input;
+        private nuint lastDecompressResult = 0;
+
+        public DecompressionStream(Stream stream, int bufferSize = 0)
+        {
+            if (stream == null)
+                throw new ArgumentNullException(nameof(stream));
+
+            if (!stream.CanRead)
+                throw new ArgumentException("Stream is not readable", nameof(stream));
+
+            if (bufferSize < 0)
+                throw new ArgumentOutOfRangeException(nameof(bufferSize));
+
+            innerStream = stream;
+            decompressor = new Decompressor();
+
+            inputBufferSize = bufferSize > 0 ? bufferSize : (int) Methods.ZSTD_CStreamInSize().EnsureZstdSuccess();
+            inputBuffer = ArrayPool<byte>.Shared.Rent(inputBufferSize);
+            input = new ZSTD_inBuffer_s {pos = (nuint) inputBufferSize, size = (nuint) inputBufferSize};
+        }
+
+        public void SetParameter(ZSTD_dParameter parameter, int value)
+        {
+            EnsureNotDisposed();
+            decompressor.SetParameter(parameter, value);
+        }
+
+        public int GetParameter(ZSTD_dParameter parameter)
+        {
+            EnsureNotDisposed();
+            return decompressor.GetParameter(parameter);
+        }
+
+        public void LoadDictionary(byte[] dict)
+        {
+            EnsureNotDisposed();
+            decompressor.LoadDictionary(dict);
+        }
+
+        ~DecompressionStream() => Dispose(false);
+
+        protected override void Dispose(bool disposing)
+        {
+            if (decompressor == null)
+                return;
+
+            decompressor.Dispose();
+            ArrayPool<byte>.Shared.Return(inputBuffer);
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+            => Read(new Span<byte>(buffer, offset, count));
+
+#if !NETSTANDARD2_0 && !NETFRAMEWORK
+        public override int Read(Span<byte> buffer)
+#else
+        public int Read(Span<byte> buffer)
+#endif
+        {
+            EnsureNotDisposed();
+
+            var output = new ZSTD_outBuffer_s {pos = 0, size = (nuint) buffer.Length};
+            while (output.pos < output.size)
+            {
+                if (input.pos >= input.size)
+                {
+                    int bytesRead;
+                    if ((bytesRead = innerStream.Read(inputBuffer, 0, inputBufferSize)) == 0)
+                    {
+                        if (lastDecompressResult != 0)
+                            throw new EndOfStreamException("Premature end of stream");
+
+                        break;
+                    }
+
+                    input.size = (nuint) bytesRead;
+                    input.pos = 0;
+                }
+
+                lastDecompressResult = DecompressStream(ref output, buffer);
+            }
+
+            return (int) output.pos;
+        }
+
+        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+            => ReadAsync(new Memory<byte>(buffer, offset, count), cancellationToken).AsTask();
+
+#if !NETSTANDARD2_0 && !NET461
+        public override async ValueTask<int> ReadAsync(Memory<byte> buffer,
+            CancellationToken cancellationToken = default)
+#else
+        public async ValueTask<int> ReadAsync(Memory<byte> buffer,
+            CancellationToken cancellationToken = default)
+#endif
+        {
+            EnsureNotDisposed();
+
+            var output = new ZSTD_outBuffer_s { pos = 0, size = (nuint)buffer.Length};
+            while (output.pos < output.size)
+            {
+                if (input.pos >= input.size)
+                {
+                    int bytesRead;
+                    if ((bytesRead = await innerStream.ReadAsync(inputBuffer, 0, inputBufferSize, cancellationToken)
+                        .ConfigureAwait(false)) == 0)
+                    {
+                        if (lastDecompressResult != 0)
+                            throw new EndOfStreamException("Premature end of stream");
+
+                        break;
+                    }
+
+                    input.size = (nuint) bytesRead;
+                    input.pos = 0;
+                }
+
+                lastDecompressResult = DecompressStream(ref output, buffer.Span);
+            }
+
+            return (int) output.pos;
+        }
+
+        private unsafe nuint DecompressStream(ref ZSTD_outBuffer_s output, Span<byte> outputBuffer)
+        {
+            fixed (byte* inputBufferPtr = inputBuffer)
+            fixed (byte* outputBufferPtr = outputBuffer)
+            {
+                input.src = inputBufferPtr;
+                output.dst = outputBufferPtr;
+                return decompressor.DecompressStream(ref input, ref output);
+            }
+        }
+
+        public override bool CanRead => true;
+        public override bool CanSeek => false;
+        public override bool CanWrite => false;
+
+        public override long Length => throw new NotSupportedException();
+
+        public override long Position
+        {
+            get => throw new NotSupportedException();
+            set => throw new NotSupportedException();
+        }
+
+        public override void Flush() => throw new NotSupportedException();
+
+        public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
+        public override void SetLength(long value) => throw new NotSupportedException();
+        public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
+
+        private void EnsureNotDisposed()
+        {
+            if (decompressor == null)
+                throw new ObjectDisposedException(nameof(DecompressionStream));
+        }
+
+#if NETSTANDARD2_0 || NET461
+        public virtual ValueTask DisposeAsync()
+        {
+            try
+            {
+                Dispose();
+                return default;
+            }
+            catch (Exception exc)
+            {
+                return new ValueTask(Task.FromException(exc));
+            }
+        }
+#endif
+    }
+}

src/SharpCompress/Compressors/Zstd/Decompressor.cs

@@ -0,0 +1,149 @@
+using System;
+using ZstdSharp.Unsafe;
+
+namespace ZstdSharp
+{
+    public unsafe class Decompressor : IDisposable
+    {
+        private ZSTD_DCtx_s* dctx;
+
+        public Decompressor()
+        {
+            dctx = Methods.ZSTD_createDCtx();
+            if (dctx == null)
+                throw new ZstdException(ZSTD_ErrorCode.ZSTD_error_GENERIC, "Failed to create dctx");
+        }
+
+        ~Decompressor()
+        {
+            ReleaseUnmanagedResources();
+        }
+
+        public void SetParameter(ZSTD_dParameter parameter, int value)
+        {
+            EnsureNotDisposed();
+            Methods.ZSTD_DCtx_setParameter(dctx, parameter, value).EnsureZstdSuccess();
+        }
+
+        public int GetParameter(ZSTD_dParameter parameter)
+        {
+            EnsureNotDisposed();
+            int value;
+            Methods.ZSTD_DCtx_getParameter(dctx, parameter, &value).EnsureZstdSuccess();
+            return value;
+        }
+
+        public void LoadDictionary(byte[] dict)
+        {
+            EnsureNotDisposed();
+            if (dict == null)
+            {
+                Methods.ZSTD_DCtx_loadDictionary(dctx, null, 0).EnsureZstdSuccess();
+            }
+            else
+            {
+                fixed (byte* dictPtr = dict)
+                    Methods.ZSTD_DCtx_loadDictionary(dctx, dictPtr, (nuint) dict.Length).EnsureZstdSuccess();
+            }
+        }
+
+        public static ulong GetDecompressedSize(ReadOnlySpan<byte> src)
+        {
+            fixed (byte* srcPtr = src)
+                return Methods.ZSTD_decompressBound(srcPtr, (nuint) src.Length).EnsureContentSizeOk();
+        }
+
+        public static ulong GetDecompressedSize(ArraySegment<byte> src)
+            => GetDecompressedSize((ReadOnlySpan<byte>) src);
+
+        public static ulong GetDecompressedSize(byte[] src, int srcOffset, int srcLength)
+            => GetDecompressedSize(new ReadOnlySpan<byte>(src, srcOffset, srcLength));
+
+        public Span<byte> Unwrap(ReadOnlySpan<byte> src, int maxDecompressedSize = int.MaxValue)
+        {
+            var expectedDstSize = GetDecompressedSize(src);
+            if (expectedDstSize > (ulong) maxDecompressedSize)
+                throw new ZstdException(ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall,
+                    $"Decompressed content size {expectedDstSize} is greater than {nameof(maxDecompressedSize)} {maxDecompressedSize}");
+            if (expectedDstSize > Constants.MaxByteArrayLength)
+                throw new ZstdException(ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall,
+                    $"Decompressed content size {expectedDstSize} is greater than max possible byte array size {Constants.MaxByteArrayLength}");
+
+            var dest = new byte[expectedDstSize];
+            var length = Unwrap(src, dest);
+            return new Span<byte>(dest, 0, length);
+        }
+
+        public int Unwrap(byte[] src, byte[] dest, int offset) 
+            => Unwrap(src, new Span<byte>(dest, offset, dest.Length - offset));
+
+        public int Unwrap(ReadOnlySpan<byte> src, Span<byte> dest)
+        {
+            EnsureNotDisposed();
+            fixed (byte* srcPtr = src)
+            fixed (byte* destPtr = dest)
+                return (int) Methods
+                    .ZSTD_decompressDCtx(dctx, destPtr, (nuint) dest.Length, srcPtr, (nuint) src.Length)
+                    .EnsureZstdSuccess();
+        }
+
+        public int Unwrap(byte[] src, int srcOffset, int srcLength, byte[] dst, int dstOffset, int dstLength)
+            => Unwrap(new ReadOnlySpan<byte>(src, srcOffset, srcLength), new Span<byte>(dst, dstOffset, dstLength));
+
+        public bool TryUnwrap(byte[] src, byte[] dest, int offset, out int written)
+            => TryUnwrap(src, new Span<byte>(dest, offset, dest.Length - offset), out written);
+
+        public bool TryUnwrap(ReadOnlySpan<byte> src, Span<byte> dest, out int written)
+        {
+            EnsureNotDisposed();
+            fixed (byte* srcPtr = src)
+            fixed (byte* destPtr = dest)
+            {
+                var returnValue =
+                    Methods.ZSTD_decompressDCtx(dctx, destPtr, (nuint) dest.Length, srcPtr, (nuint) src.Length);
+
+                if (returnValue == unchecked(0 - (nuint)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall))
+                {
+                    written = default;
+                    return false;
+                }
+
+                returnValue.EnsureZstdSuccess();
+                written = (int) returnValue;
+                return true;
+            }
+        }
+
+        public bool TryUnwrap(byte[] src, int srcOffset, int srcLength, byte[] dst, int dstOffset, int dstLength, out int written)
+            => TryUnwrap(new ReadOnlySpan<byte>(src, srcOffset, srcLength), new Span<byte>(dst, dstOffset, dstLength), out written);
+
+        private void ReleaseUnmanagedResources()
+        {
+            if (dctx != null)
+            {
+                Methods.ZSTD_freeDCtx(dctx);
+                dctx = null;
+            }
+        }
+
+        public void Dispose()
+        {
+            ReleaseUnmanagedResources();
+            GC.SuppressFinalize(this);
+        }
+        private void EnsureNotDisposed()
+        {
+            if (dctx == null)
+                throw new ObjectDisposedException(nameof(Decompressor));
+        }
+
+        internal nuint DecompressStream(ref ZSTD_inBuffer_s input, ref ZSTD_outBuffer_s output)
+        {
+            fixed (ZSTD_inBuffer_s* inputPtr = &input)
+            fixed (ZSTD_outBuffer_s* outputPtr = &output)
+            {
+                return Methods.ZSTD_decompressStream(dctx, outputPtr, inputPtr).EnsureZstdSuccess();
+            }
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/DictBuilder.cs

@@ -0,0 +1,39 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using ZstdSharp.Unsafe;
+
+namespace ZstdSharp
+{
+    public static unsafe class DictBuilder
+    {
+        public static byte[] TrainFromBuffer(IEnumerable<byte[]> samples, int dictCapacity = DefaultDictCapacity)
+        {
+            var ms = new MemoryStream();
+            var samplesSizes = samples.Select(sample =>
+            {
+                ms.Write(sample, 0, sample.Length);
+                return (nuint) sample.Length;
+            }).ToArray();
+
+            var dictBuffer = new byte[dictCapacity];
+            fixed (byte* dictBufferPtr = dictBuffer)
+            fixed (byte* samplesBufferPtr = ms.GetBuffer())
+            fixed (nuint* samplesSizesPtr = samplesSizes)
+            {
+                var dictSize = (int) Methods
+                    .ZDICT_trainFromBuffer(dictBufferPtr, (nuint) dictCapacity, samplesBufferPtr, samplesSizesPtr,
+                        (uint) samplesSizes.Length)
+                    .EnsureZdictSuccess();
+
+                if (dictCapacity != dictSize)
+                    Array.Resize(ref dictBuffer, dictSize);
+
+                return dictBuffer;
+            }
+        }
+
+        public const int DefaultDictCapacity = 112640; // Used by zstd utility by default
+    }
+}

src/SharpCompress/Compressors/Zstd/Polyfills/BitOperations.cs

@@ -0,0 +1,201 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#if !NETCOREAPP3_0_OR_GREATER
+
+using System.Runtime.CompilerServices;
+using static ZstdSharp.UnsafeHelper;
+
+// Some routines inspired by the Stanford Bit Twiddling Hacks by Sean Eron Anderson:
+// http://graphics.stanford.edu/~seander/bithacks.html
+
+namespace System.Numerics
+{
+    /// <summary>
+    /// Utility methods for intrinsic bit-twiddling operations.
+    /// The methods use hardware intrinsics when available on the underlying platform,
+    /// otherwise they use optimized software fallbacks.
+    /// </summary>
+    public static unsafe class BitOperations
+    {
+        // hack: should be public because of inline
+        public static readonly byte* TrailingZeroCountDeBruijn = GetArrayPointer(new byte[]
+        {
+            00, 01, 28, 02, 29, 14, 24, 03,
+            30, 22, 20, 15, 25, 17, 04, 08,
+            31, 27, 13, 23, 21, 19, 16, 07,
+            26, 12, 18, 06, 11, 05, 10, 09
+        });
+
+        // hack: should be public because of inline
+        public static readonly byte* Log2DeBruijn = GetArrayPointer(new byte[]
+        {
+            00, 09, 01, 10, 13, 21, 02, 29,
+            11, 14, 16, 18, 22, 25, 03, 30,
+            08, 12, 20, 28, 15, 17, 24, 07,
+            19, 27, 23, 06, 26, 05, 04, 31
+        });
+
+        /// <summary>
+        /// Returns the integer (floor) log of the specified value, base 2.
+        /// Note that by convention, input value 0 returns 0 since log(0) is undefined.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int Log2(uint value)
+        {
+            // The 0->0 contract is fulfilled by setting the LSB to 1.
+            // Log(1) is 0, and setting the LSB for values > 1 does not change the log2 result.
+            value |= 1;
+
+            // value    lzcnt   actual  expected
+            // ..0001   31      31-31    0
+            // ..0010   30      31-30    1
+            // 0010..    2      31-2    29
+            // 0100..    1      31-1    30
+            // 1000..    0      31-0    31
+
+            // Fallback contract is 0->0
+            // No AggressiveInlining due to large method size
+            // Has conventional contract 0->0 (Log(0) is undefined)
+
+            // Fill trailing zeros with ones, eg 00010010 becomes 00011111
+            value |= value >> 01;
+            value |= value >> 02;
+            value |= value >> 04;
+            value |= value >> 08;
+            value |= value >> 16;
+
+            // uint.MaxValue >> 27 is always in range [0 - 31] so we use Unsafe.AddByteOffset to avoid bounds check
+            return Log2DeBruijn[
+                // Using deBruijn sequence, k=2, n=5 (2^5=32) : 0b_0000_0111_1100_0100_1010_1100_1101_1101u
+                (int)((value * 0x07C4ACDDu) >> 27)];
+        }
+
+        /// <summary>
+        /// Returns the integer (floor) log of the specified value, base 2.
+        /// Note that by convention, input value 0 returns 0 since log(0) is undefined.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int Log2(ulong value)
+        {
+            value |= 1;
+
+            uint hi = (uint)(value >> 32);
+
+            if (hi == 0)
+            {
+                return Log2((uint)value);
+            }
+
+            return 32 + Log2(hi);
+        }
+
+        /// <summary>
+        /// Count the number of trailing zero bits in an integer value.
+        /// Similar in behavior to the x86 instruction TZCNT.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int TrailingZeroCount(int value)
+            => TrailingZeroCount((uint)value);
+
+        /// <summary>
+        /// Count the number of trailing zero bits in an integer value.
+        /// Similar in behavior to the x86 instruction TZCNT.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int TrailingZeroCount(uint value)
+        {
+            // Unguarded fallback contract is 0->0, BSF contract is 0->undefined
+            if (value == 0)
+            {
+                return 32;
+            }
+
+            // uint.MaxValue >> 27 is always in range [0 - 31] so we use Unsafe.AddByteOffset to avoid bounds check
+            return TrailingZeroCountDeBruijn[
+                // Using deBruijn sequence, k=2, n=5 (2^5=32) : 0b_0000_0111_0111_1100_1011_0101_0011_0001u
+                (int)(((value & (uint)-(int)value) * 0x077CB531u) >> 27)]; // Multi-cast mitigates redundant conv.u8
+        }
+
+        /// <summary>
+        /// Count the number of trailing zero bits in a mask.
+        /// Similar in behavior to the x86 instruction TZCNT.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int TrailingZeroCount(long value)
+            => TrailingZeroCount((ulong)value);
+
+        /// <summary>
+        /// Count the number of trailing zero bits in a mask.
+        /// Similar in behavior to the x86 instruction TZCNT.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int TrailingZeroCount(ulong value)
+        {
+            uint lo = (uint)value;
+
+            if (lo == 0)
+            {
+                return 32 + TrailingZeroCount((uint)(value >> 32));
+            }
+
+            return TrailingZeroCount(lo);
+        }
+
+        /// <summary>
+        /// Rotates the specified value left by the specified number of bits.
+        /// Similar in behavior to the x86 instruction ROL.
+        /// </summary>
+        /// <param name="value">The value to rotate.</param>
+        /// <param name="offset">The number of bits to rotate by.
+        /// Any value outside the range [0..31] is treated as congruent mod 32.</param>
+        /// <returns>The rotated value.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint RotateLeft(uint value, int offset)
+            => (value << offset) | (value >> (32 - offset));
+
+        /// <summary>
+        /// Rotates the specified value left by the specified number of bits.
+        /// Similar in behavior to the x86 instruction ROL.
+        /// </summary>
+        /// <param name="value">The value to rotate.</param>
+        /// <param name="offset">The number of bits to rotate by.
+        /// Any value outside the range [0..63] is treated as congruent mod 64.</param>
+        /// <returns>The rotated value.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ulong RotateLeft(ulong value, int offset)
+            => (value << offset) | (value >> (64 - offset));
+
+        /// <summary>
+        /// Rotates the specified value right by the specified number of bits.
+        /// Similar in behavior to the x86 instruction ROR.
+        /// </summary>
+        /// <param name="value">The value to rotate.</param>
+        /// <param name="offset">The number of bits to rotate by.
+        /// Any value outside the range [0..31] is treated as congruent mod 32.</param>
+        /// <returns>The rotated value.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint RotateRight(uint value, int offset)
+            => (value >> offset) | (value << (32 - offset));
+
+        /// <summary>
+        /// Rotates the specified value right by the specified number of bits.
+        /// Similar in behavior to the x86 instruction ROR.
+        /// </summary>
+        /// <param name="value">The value to rotate.</param>
+        /// <param name="offset">The number of bits to rotate by.
+        /// Any value outside the range [0..63] is treated as congruent mod 64.</param>
+        /// <returns>The rotated value.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ulong RotateRight(ulong value, int offset)
+            => (value >> offset) | (value << (64 - offset));
+    }
+}
+
+#endif

src/SharpCompress/Compressors/Zstd/Polyfills/SkipLocalsInitAttribute.cs

@@ -0,0 +1,25 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#if !NET5_0_OR_GREATER
+namespace System.Runtime.CompilerServices
+{
+    /// <summary>
+    /// Used to indicate to the compiler that the <c>.locals init</c> flag should not be set in method headers.
+    /// </summary>
+    /// <remarks>Internal copy of the .NET 5 attribute.</remarks>
+    [AttributeUsage(
+        AttributeTargets.Module |
+        AttributeTargets.Class |
+        AttributeTargets.Struct |
+        AttributeTargets.Interface |
+        AttributeTargets.Constructor |
+        AttributeTargets.Method |
+        AttributeTargets.Property |
+        AttributeTargets.Event,
+        Inherited = false)]
+    internal sealed class SkipLocalsInitAttribute : Attribute
+    {
+    }
+}
+#endif

src/SharpCompress/Compressors/Zstd/Polyfills/Vector128.cs

@@ -0,0 +1,54 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#if !NETCOREAPP3_0_OR_GREATER
+
+using System.Runtime.CompilerServices;
+
+namespace System.Runtime.Intrinsics
+{
+    public static class Vector128
+    {
+        internal const int Size = 16;
+
+        public static unsafe Vector128<byte> Create(byte value)
+        {
+            byte* pResult = stackalloc byte[16]
+            {
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+                value,
+            };
+
+            return Unsafe.AsRef<Vector128<byte>>(pResult);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector128<U> As<T, U>(this Vector128<T> vector)
+            where T : struct
+            where U : struct =>
+            Unsafe.As<Vector128<T>, Vector128<U>>(ref vector);
+
+        public static T GetElement<T>(this Vector128<T> vector, int index)
+            where T : struct
+        {
+            ref T e0 = ref Unsafe.As<Vector128<T>, T>(ref vector);
+            return Unsafe.Add(ref e0, index);
+        }
+    }
+}
+
+#endif

src/SharpCompress/Compressors/Zstd/Polyfills/Vector128_1.cs

@@ -0,0 +1,36 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#if !NETCOREAPP3_0_OR_GREATER
+
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace System.Runtime.Intrinsics
+{
+    [StructLayout(LayoutKind.Sequential, Size = Vector128.Size)]
+    public readonly struct Vector128<T> : IEquatable<Vector128<T>>
+        where T : struct
+    {
+        private readonly ulong _00;
+        private readonly ulong _01;
+
+        public static int Count => Vector128.Size / Unsafe.SizeOf<T>();
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool Equals(Vector128<T> other)
+        {
+            for (int i = 0; i < Count; i++)
+            {
+                if (!((IEquatable<T>)(this.GetElement(i))).Equals(other.GetElement(i)))
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+    }
+}
+
+#endif

src/SharpCompress/Compressors/Zstd/ThrowHelper.cs

@@ -0,0 +1,43 @@
+using ZstdSharp.Unsafe;
+
+namespace ZstdSharp
+{
+    public static unsafe class ThrowHelper
+    {
+        private const ulong ZSTD_CONTENTSIZE_UNKNOWN = unchecked(0UL - 1);
+        private const ulong ZSTD_CONTENTSIZE_ERROR = unchecked(0UL - 2);
+
+        public static nuint EnsureZstdSuccess(this nuint returnValue)
+        {
+            if (Methods.ZSTD_isError(returnValue) != 0)
+                ThrowException(returnValue, Methods.ZSTD_getErrorName(returnValue));
+
+            return returnValue;
+        }
+
+        public static nuint EnsureZdictSuccess(this nuint returnValue)
+        {
+            if (Methods.ZDICT_isError(returnValue) != 0)
+                ThrowException(returnValue, Methods.ZDICT_getErrorName(returnValue));
+
+            return returnValue;
+        }
+
+        public static ulong EnsureContentSizeOk(this ulong returnValue)
+        {
+            if (returnValue == ZSTD_CONTENTSIZE_UNKNOWN)
+                throw new ZstdException(ZSTD_ErrorCode.ZSTD_error_GENERIC, "Decompressed content size is not specified");
+
+            if (returnValue == ZSTD_CONTENTSIZE_ERROR)
+                throw new ZstdException(ZSTD_ErrorCode.ZSTD_error_GENERIC, "Decompressed content size cannot be determined (e.g. invalid magic number, srcSize too small)");
+
+            return returnValue;
+        }
+
+        private static void ThrowException(nuint returnValue, string message)
+        {
+            var code = 0 - returnValue;
+            throw new ZstdException((ZSTD_ErrorCode) code, message);
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/Arrays.cs

@@ -0,0 +1,368 @@
+using System;
+using static ZstdSharp.UnsafeHelper;
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        static uint* rtbTable = GetArrayPointer(new uint[8] {
+            0,
+            473195,
+            504333,
+            520860,
+            550000,
+            700000,
+            750000,
+            830000,
+        });
+        static byte* LL_Code = GetArrayPointer(new byte[64] 
+        {
+            0,
+            1,
+            2,
+            3,
+            4,
+            5,
+            6,
+            7,
+            8,
+            9,
+            10,
+            11,
+            12,
+            13,
+            14,
+            15,
+            16,
+            16,
+            17,
+            17,
+            18,
+            18,
+            19,
+            19,
+            20,
+            20,
+            20,
+            20,
+            21,
+            21,
+            21,
+            21,
+            22,
+            22,
+            22,
+            22,
+            22,
+            22,
+            22,
+            22,
+            23,
+            23,
+            23,
+            23,
+            23,
+            23,
+            23,
+            23,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+            24,
+        });
+        static byte* ML_Code = GetArrayPointer(new byte[128] 
+        {
+            0,
+            1,
+            2,
+            3,
+            4,
+            5,
+            6,
+            7,
+            8,
+            9,
+            10,
+            11,
+            12,
+            13,
+            14,
+            15,
+            16,
+            17,
+            18,
+            19,
+            20,
+            21,
+            22,
+            23,
+            24,
+            25,
+            26,
+            27,
+            28,
+            29,
+            30,
+            31,
+            32,
+            32,
+            33,
+            33,
+            34,
+            34,
+            35,
+            35,
+            36,
+            36,
+            36,
+            36,
+            37,
+            37,
+            37,
+            37,
+            38,
+            38,
+            38,
+            38,
+            38,
+            38,
+            38,
+            38,
+            39,
+            39,
+            39,
+            39,
+            39,
+            39,
+            39,
+            39,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            40,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            41,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+            42,
+        });
+        static ulong* srcSizeTiers = GetArrayPointer(new ulong[4] 
+        {
+            16 * (1 << 10),
+            128 * (1 << 10),
+            256 * (1 << 10),
+            (unchecked(0UL - 1)),
+        });
+        static ZSTD_blockCompressor?[][] blockCompressor = new ZSTD_blockCompressor?[4][] 
+                                                           {
+                                                               new ZSTD_blockCompressor[10]
+                                                               {
+                                                                   ZSTD_compressBlock_fast,
+                                                                   ZSTD_compressBlock_fast,
+                                                                   ZSTD_compressBlock_doubleFast,
+                                                                   ZSTD_compressBlock_greedy,
+                                                                   ZSTD_compressBlock_lazy,
+                                                                   ZSTD_compressBlock_lazy2,
+                                                                   ZSTD_compressBlock_btlazy2,
+                                                                   ZSTD_compressBlock_btopt,
+                                                                   ZSTD_compressBlock_btultra,
+                                                                   ZSTD_compressBlock_btultra2,
+                                                               },
+                                                               new ZSTD_blockCompressor[10]
+                                                               {
+                                                                   ZSTD_compressBlock_fast_extDict,
+                                                                   ZSTD_compressBlock_fast_extDict,
+                                                                   ZSTD_compressBlock_doubleFast_extDict,
+                                                                   ZSTD_compressBlock_greedy_extDict,
+                                                                   ZSTD_compressBlock_lazy_extDict,
+                                                                   ZSTD_compressBlock_lazy2_extDict,
+                                                                   ZSTD_compressBlock_btlazy2_extDict,
+                                                                   ZSTD_compressBlock_btopt_extDict,
+                                                                   ZSTD_compressBlock_btultra_extDict,
+                                                                   ZSTD_compressBlock_btultra_extDict,
+                                                               },
+                                                               new ZSTD_blockCompressor[10]
+                                                               {
+                                                                   ZSTD_compressBlock_fast_dictMatchState,
+                                                                   ZSTD_compressBlock_fast_dictMatchState,
+                                                                   ZSTD_compressBlock_doubleFast_dictMatchState,
+                                                                   ZSTD_compressBlock_greedy_dictMatchState,
+                                                                   ZSTD_compressBlock_lazy_dictMatchState,
+                                                                   ZSTD_compressBlock_lazy2_dictMatchState,
+                                                                   ZSTD_compressBlock_btlazy2_dictMatchState,
+                                                                   ZSTD_compressBlock_btopt_dictMatchState,
+                                                                   ZSTD_compressBlock_btultra_dictMatchState,
+                                                                   ZSTD_compressBlock_btultra_dictMatchState,
+                                                               },
+                                                               new ZSTD_blockCompressor?[10]
+                                                               {
+                                                                   null,
+                                                                   null,
+                                                                   null,
+                                                                   ZSTD_compressBlock_greedy_dedicatedDictSearch,
+                                                                   ZSTD_compressBlock_lazy_dedicatedDictSearch,
+                                                                   ZSTD_compressBlock_lazy2_dedicatedDictSearch,
+                                                                   null,
+                                                                   null,
+                                                                   null,
+                                                                   null,
+                                                               },
+                                                           };
+        static ZSTD_blockCompressor[][] rowBasedBlockCompressors = new ZSTD_blockCompressor[4][] 
+        {
+            new ZSTD_blockCompressor[3]
+            {
+                ZSTD_compressBlock_greedy_row,
+                ZSTD_compressBlock_lazy_row,
+                ZSTD_compressBlock_lazy2_row,
+            },
+            new ZSTD_blockCompressor[3]
+            {
+                ZSTD_compressBlock_greedy_extDict_row,
+                ZSTD_compressBlock_lazy_extDict_row,
+                ZSTD_compressBlock_lazy2_extDict_row,
+            },
+            new ZSTD_blockCompressor[3]
+            {
+                ZSTD_compressBlock_greedy_dictMatchState_row,
+                ZSTD_compressBlock_lazy_dictMatchState_row,
+                ZSTD_compressBlock_lazy2_dictMatchState_row,
+            },
+            new ZSTD_blockCompressor[3]
+            {
+                ZSTD_compressBlock_greedy_dedicatedDictSearch_row,
+                ZSTD_compressBlock_lazy_dedicatedDictSearch_row,
+                ZSTD_compressBlock_lazy2_dedicatedDictSearch_row,
+            },
+        };
+        static searchMax_f?[][] searchFuncs = new searchMax_f?[4][] 
+                                              {
+                                                  new searchMax_f[3]
+                                                  {
+                                                      ZSTD_HcFindBestMatch_selectMLS,
+                                                      ZSTD_BtFindBestMatch_selectMLS,
+                                                      ZSTD_RowFindBestMatch_selectRowLog,
+                                                  },
+                                                  new searchMax_f?[3]
+                                                  {
+                                                      null,
+                                                      null,
+                                                      null,
+                                                  },
+                                                  new searchMax_f[3]
+                                                  {
+                                                      ZSTD_HcFindBestMatch_dictMatchState_selectMLS,
+                                                      ZSTD_BtFindBestMatch_dictMatchState_selectMLS,
+                                                      ZSTD_RowFindBestMatch_dictMatchState_selectRowLog,
+                                                  },
+                                                  new searchMax_f?[3]
+                                                  {
+                                                      ZSTD_HcFindBestMatch_dedicatedDictSearch_selectMLS,
+                                                      null,
+                                                      ZSTD_RowFindBestMatch_dedicatedDictSearch_selectRowLog,
+                                                  },
+                                              };
+        static searchMax_f[] searchFuncsExtGeneric = new searchMax_f[3] 
+        {
+            ZSTD_HcFindBestMatch_extDict_selectMLS,
+            ZSTD_BtFindBestMatch_extDict_selectMLS,
+            ZSTD_RowFindBestMatch_extDict_selectRowLog,
+        };
+        static decompressionAlgo[] decompress = new decompressionAlgo[2] 
+        {
+            HUF_decompress4X1,
+            HUF_decompress4X2,
+        };
+        static uint* dec32table = GetArrayPointer(new uint[8] 
+        {
+            0,
+            1,
+            2,
+            1,
+            4,
+            4,
+            4,
+            4,
+        });
+        static int* dec64table = GetArrayPointer(new int[8] 
+        {
+            8,
+            8,
+            8,
+            7,
+            8,
+            9,
+            10,
+            11,
+        });
+
+        private static byte* emptyString = GetArrayPointer(new byte[] {0});
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/BIT_CStream_t.cs

@@ -0,0 +1,24 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /*-******************************************
+    *  bitStream encoding API (write forward)
+    ********************************************/
+    /* bitStream can mix input from multiple sources.
+     * A critical property of these streams is that they encode and decode in **reverse** direction.
+     * So the first bit sequence you add will be the last to be read, like a LIFO stack.
+     */
+    public unsafe partial struct BIT_CStream_t
+    {
+        public nuint bitContainer;
+
+        public uint bitPos;
+
+        public sbyte* startPtr;
+
+        public sbyte* ptr;
+
+        public sbyte* endPtr;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/BIT_DStream_status.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public enum BIT_DStream_status
+    {
+        BIT_DStream_unfinished = 0,
+        BIT_DStream_endOfBuffer = 1,
+        BIT_DStream_completed = 2,
+        BIT_DStream_overflow = 3,
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/BIT_DStream_t.cs

@@ -0,0 +1,20 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /*-********************************************
+    *  bitStream decoding API (read backward)
+    **********************************************/
+    public unsafe partial struct BIT_DStream_t
+    {
+        public nuint bitContainer;
+
+        public uint bitsConsumed;
+
+        public sbyte* ptr;
+
+        public sbyte* start;
+
+        public sbyte* limitPtr;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/Bitstream.cs

@@ -0,0 +1,420 @@
+using System;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using static ZstdSharp.UnsafeHelper;
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        /*-**************************************************************
+        *  Internal functions
+        ****************************************************************/
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static uint BIT_highbit32(uint val)
+        {
+            assert(val != 0);
+
+            {
+                return (uint) BitOperations.Log2(val);
+            }
+        }
+
+        public static uint* BIT_mask = GetArrayPointer(new uint[32]
+        {
+            0,
+            1,
+            3,
+            7,
+            0xF,
+            0x1F,
+            0x3F,
+            0x7F,
+            0xFF,
+            0x1FF,
+            0x3FF,
+            0x7FF,
+            0xFFF,
+            0x1FFF,
+            0x3FFF,
+            0x7FFF,
+            0xFFFF,
+            0x1FFFF,
+            0x3FFFF,
+            0x7FFFF,
+            0xFFFFF,
+            0x1FFFFF,
+            0x3FFFFF,
+            0x7FFFFF,
+            0xFFFFFF,
+            0x1FFFFFF,
+            0x3FFFFFF,
+            0x7FFFFFF,
+            0xFFFFFFF,
+            0x1FFFFFFF,
+            0x3FFFFFFF,
+            0x7FFFFFFF,
+        });
+
+        /*-**************************************************************
+        *  bitStream encoding
+        ****************************************************************/
+        /*! BIT_initCStream() :
+         *  `dstCapacity` must be > sizeof(size_t)
+         *  @return : 0 if success,
+         *            otherwise an error code (can be tested using ERR_isError()) */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint BIT_initCStream(BIT_CStream_t* bitC, void* startPtr, nuint dstCapacity)
+        {
+            bitC->bitContainer = 0;
+            bitC->bitPos = 0;
+            bitC->startPtr = (sbyte*)(startPtr);
+            bitC->ptr = bitC->startPtr;
+            bitC->endPtr = bitC->startPtr + dstCapacity - (nuint)(sizeof(nuint));
+            if (dstCapacity <= (nuint)(sizeof(nuint)))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall)));
+            }
+
+            return 0;
+        }
+
+        /*! BIT_addBits() :
+         *  can add up to 31 bits into `bitC`.
+         *  Note : does not check for register overflow ! */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void BIT_addBits(BIT_CStream_t* bitC, nuint value, uint nbBits)
+        {
+            assert(nbBits < ((nuint)(sizeof(uint) * 32) / (nuint)(sizeof(uint))));
+            assert(nbBits + bitC->bitPos < (nuint)(sizeof(nuint)) * 8);
+            bitC->bitContainer |= (value & BIT_mask[nbBits]) << (int)bitC->bitPos;
+            bitC->bitPos += nbBits;
+        }
+
+        /*! BIT_addBitsFast() :
+         *  works only if `value` is _clean_,
+         *  meaning all high bits above nbBits are 0 */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void BIT_addBitsFast(BIT_CStream_t* bitC, nuint value, uint nbBits)
+        {
+            assert((value >> (int)nbBits) == 0);
+            assert(nbBits + bitC->bitPos < (nuint)(sizeof(nuint)) * 8);
+            bitC->bitContainer |= value << (int)bitC->bitPos;
+            bitC->bitPos += nbBits;
+        }
+
+        /*! BIT_flushBitsFast() :
+         *  assumption : bitContainer has not overflowed
+         *  unsafe version; does not check buffer overflow */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void BIT_flushBitsFast(BIT_CStream_t* bitC)
+        {
+            nuint nbBytes = bitC->bitPos >> 3;
+
+            assert(bitC->bitPos < (nuint)(sizeof(nuint)) * 8);
+            assert(bitC->ptr <= bitC->endPtr);
+            MEM_writeLEST((void*)bitC->ptr, bitC->bitContainer);
+            bitC->ptr += nbBytes;
+            bitC->bitPos &= 7;
+            bitC->bitContainer >>= (int)(nbBytes * 8);
+        }
+
+        /*! BIT_flushBits() :
+         *  assumption : bitContainer has not overflowed
+         *  safe version; check for buffer overflow, and prevents it.
+         *  note : does not signal buffer overflow.
+         *  overflow will be revealed later on using BIT_closeCStream() */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void BIT_flushBits(BIT_CStream_t* bitC)
+        {
+            nuint nbBytes = bitC->bitPos >> 3;
+
+            assert(bitC->bitPos < (nuint)(sizeof(nuint)) * 8);
+            assert(bitC->ptr <= bitC->endPtr);
+            MEM_writeLEST((void*)bitC->ptr, bitC->bitContainer);
+            bitC->ptr += nbBytes;
+            if (bitC->ptr > bitC->endPtr)
+            {
+                bitC->ptr = bitC->endPtr;
+            }
+
+            bitC->bitPos &= 7;
+            bitC->bitContainer >>= (int)(nbBytes * 8);
+        }
+
+        /*! BIT_closeCStream() :
+         *  @return : size of CStream, in bytes,
+         *            or 0 if it could not fit into dstBuffer */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint BIT_closeCStream(BIT_CStream_t* bitC)
+        {
+            BIT_addBitsFast(bitC, 1, 1);
+            BIT_flushBits(bitC);
+            if (bitC->ptr >= bitC->endPtr)
+            {
+                return 0;
+            }
+
+            return (nuint)((bitC->ptr - bitC->startPtr) + (((bitC->bitPos > 0)) ? 1 : 0));
+        }
+
+        /*-********************************************************
+        *  bitStream decoding
+        **********************************************************/
+        /*! BIT_initDStream() :
+         *  Initialize a BIT_DStream_t.
+         * `bitD` : a pointer to an already allocated BIT_DStream_t structure.
+         * `srcSize` must be the *exact* size of the bitStream, in bytes.
+         * @return : size of stream (== srcSize), or an errorCode if a problem is detected
+         */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint BIT_initDStream(BIT_DStream_t* bitD, void* srcBuffer, nuint srcSize)
+        {
+            if (srcSize < 1)
+            {
+                memset((void*)(bitD), (0), ((nuint)(sizeof(BIT_DStream_t))));
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_srcSize_wrong)));
+            }
+
+            bitD->start = (sbyte*)(srcBuffer);
+            bitD->limitPtr = bitD->start + (nuint)(sizeof(nuint));
+            if (srcSize >= (nuint)(sizeof(nuint)))
+            {
+                bitD->ptr = (sbyte*)(srcBuffer) + srcSize - (nuint)(sizeof(nuint));
+                bitD->bitContainer = MEM_readLEST((void*)bitD->ptr);
+
+                {
+                    byte lastByte = ((byte*)(srcBuffer))[srcSize - 1];
+
+                    bitD->bitsConsumed = lastByte != 0 ? 8 - BIT_highbit32(lastByte) : 0;
+                    if (lastByte == 0)
+                    {
+                        return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+                    }
+                }
+            }
+            else
+            {
+                bitD->ptr = bitD->start;
+                bitD->bitContainer = *(byte*)(bitD->start);
+                switch (srcSize)
+                {
+                    case 7:
+                    {
+                        bitD->bitContainer += (nuint)(((byte*)(srcBuffer))[6]) << (int)((nuint)(sizeof(nuint)) * 8 - 16);
+                    }
+
+
+                    goto case 6;
+                    case 6:
+                    {
+                        bitD->bitContainer += (nuint)(((byte*)(srcBuffer))[5]) << (int)((nuint)(sizeof(nuint)) * 8 - 24);
+                    }
+
+
+                    goto case 5;
+                    case 5:
+                    {
+                        bitD->bitContainer += (nuint)(((byte*)(srcBuffer))[4]) << (int)((nuint)(sizeof(nuint)) * 8 - 32);
+                    }
+
+
+                    goto case 4;
+                    case 4:
+                    {
+                        bitD->bitContainer += (nuint)(((byte*)(srcBuffer))[3]) << 24;
+                    }
+
+
+                    goto case 3;
+                    case 3:
+                    {
+                        bitD->bitContainer += (nuint)(((byte*)(srcBuffer))[2]) << 16;
+                    }
+
+
+                    goto case 2;
+                    case 2:
+                    {
+                        bitD->bitContainer += (nuint)(((byte*)(srcBuffer))[1]) << 8;
+                    }
+
+
+                    goto default;
+                    default:
+                    {
+                        break;
+                    }
+                }
+
+
+                {
+                    byte lastByte = ((byte*)(srcBuffer))[srcSize - 1];
+
+                    bitD->bitsConsumed = lastByte != 0 ? 8 - BIT_highbit32(lastByte) : 0;
+                    if (lastByte == 0)
+                    {
+                        return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_corruption_detected)));
+                    }
+                }
+
+                bitD->bitsConsumed += (uint)((nuint)(sizeof(nuint)) - srcSize) * 8;
+            }
+
+            return srcSize;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint BIT_getUpperBits(nuint bitContainer, uint start)
+        {
+            return bitContainer >> (int)start;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint BIT_getMiddleBits(nuint bitContainer, uint start, uint nbBits)
+        {
+            uint regMask = (uint)((nuint)(sizeof(nuint)) * 8 - 1);
+
+            assert(nbBits < ((nuint)(sizeof(uint) * 32) / (nuint)(sizeof(uint))));
+            return (bitContainer >> (int)(start & regMask)) & BIT_mask[nbBits];
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint BIT_getLowerBits(nuint bitContainer, uint nbBits)
+        {
+            assert(nbBits < ((nuint)(sizeof(uint) * 32) / (nuint)(sizeof(uint))));
+            return bitContainer & BIT_mask[nbBits];
+        }
+
+        /*! BIT_lookBits() :
+         *  Provides next n bits from local register.
+         *  local register is not modified.
+         *  On 32-bits, maxNbBits==24.
+         *  On 64-bits, maxNbBits==56.
+         * @return : value extracted */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint BIT_lookBits(BIT_DStream_t* bitD, uint nbBits)
+        {
+            return BIT_getMiddleBits(bitD->bitContainer, (uint)(((nuint)(sizeof(nuint)) * 8) - bitD->bitsConsumed - nbBits), nbBits);
+        }
+
+        /*! BIT_lookBitsFast() :
+         *  unsafe version; only works if nbBits >= 1 */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint BIT_lookBitsFast(BIT_DStream_t* bitD, uint nbBits)
+        {
+            uint regMask = (uint)((nuint)(sizeof(nuint)) * 8 - 1);
+
+            assert(nbBits >= 1);
+            return (bitD->bitContainer << (int)(bitD->bitsConsumed & regMask)) >> (int)(((regMask + 1) - nbBits) & regMask);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void BIT_skipBits(BIT_DStream_t* bitD, uint nbBits)
+        {
+            bitD->bitsConsumed += nbBits;
+        }
+
+        /*! BIT_readBits() :
+         *  Read (consume) next n bits from local register and update.
+         *  Pay attention to not read more than nbBits contained into local register.
+         * @return : extracted value. */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint BIT_readBits(BIT_DStream_t* bitD, uint nbBits)
+        {
+            nuint value = BIT_lookBits(bitD, nbBits);
+
+            BIT_skipBits(bitD, nbBits);
+            return value;
+        }
+
+        /*! BIT_readBitsFast() :
+         *  unsafe version; only works only if nbBits >= 1 */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint BIT_readBitsFast(BIT_DStream_t* bitD, uint nbBits)
+        {
+            nuint value = BIT_lookBitsFast(bitD, nbBits);
+
+            assert(nbBits >= 1);
+            BIT_skipBits(bitD, nbBits);
+            return value;
+        }
+
+        /*! BIT_reloadDStreamFast() :
+         *  Similar to BIT_reloadDStream(), but with two differences:
+         *  1. bitsConsumed <= sizeof(bitD->bitContainer)*8 must hold!
+         *  2. Returns BIT_DStream_overflow when bitD->ptr < bitD->limitPtr, at this
+         *     point you must use BIT_reloadDStream() to reload.
+         */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static BIT_DStream_status BIT_reloadDStreamFast(BIT_DStream_t* bitD)
+        {
+            if ((bitD->ptr < bitD->limitPtr))
+            {
+                return BIT_DStream_status.BIT_DStream_overflow;
+            }
+
+            assert(bitD->bitsConsumed <= (nuint)(sizeof(nuint)) * 8);
+            bitD->ptr -= bitD->bitsConsumed >> 3;
+            bitD->bitsConsumed &= 7;
+            bitD->bitContainer = MEM_readLEST((void*)bitD->ptr);
+            return BIT_DStream_status.BIT_DStream_unfinished;
+        }
+
+        /*! BIT_reloadDStream() :
+         *  Refill `bitD` from buffer previously set in BIT_initDStream() .
+         *  This function is safe, it guarantees it will not read beyond src buffer.
+         * @return : status of `BIT_DStream_t` internal register.
+         *           when status == BIT_DStream_unfinished, internal register is filled with at least 25 or 57 bits */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD)
+        {
+            if (bitD->bitsConsumed > ((nuint)(sizeof(nuint)) * 8))
+            {
+                return BIT_DStream_status.BIT_DStream_overflow;
+            }
+
+            if (bitD->ptr >= bitD->limitPtr)
+            {
+                return BIT_reloadDStreamFast(bitD);
+            }
+
+            if (bitD->ptr == bitD->start)
+            {
+                if (bitD->bitsConsumed < (nuint)(sizeof(nuint)) * 8)
+                {
+                    return BIT_DStream_status.BIT_DStream_endOfBuffer;
+                }
+
+                return BIT_DStream_status.BIT_DStream_completed;
+            }
+
+
+            {
+                uint nbBytes = bitD->bitsConsumed >> 3;
+                BIT_DStream_status result = BIT_DStream_status.BIT_DStream_unfinished;
+
+                if (bitD->ptr - nbBytes < bitD->start)
+                {
+                    nbBytes = (uint)(bitD->ptr - bitD->start);
+                    result = BIT_DStream_status.BIT_DStream_endOfBuffer;
+                }
+
+                bitD->ptr -= nbBytes;
+                bitD->bitsConsumed -= nbBytes * 8;
+                bitD->bitContainer = MEM_readLEST((void*)bitD->ptr);
+                return result;
+            }
+        }
+
+        /*! BIT_endOfDStream() :
+         * @return : 1 if DStream has _exactly_ reached its end (all bits consumed).
+         */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static uint BIT_endOfDStream(BIT_DStream_t* DStream)
+        {
+            return ((((DStream->ptr == DStream->start) && (DStream->bitsConsumed == (nuint)(sizeof(nuint)) * 8))) ? 1U : 0U);
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/COVER_best_s.cs

@@ -0,0 +1,29 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /**
+     * COVER_best_t is used for two purposes:
+     * 1. Synchronizing threads.
+     * 2. Saving the best parameters and dictionary.
+     *
+     * All of the methods except COVER_best_init() are thread safe if zstd is
+     * compiled with multithreaded support.
+     */
+    public unsafe partial struct COVER_best_s
+    {
+        public int mutex;
+
+        public int cond;
+
+        public nuint liveJobs;
+
+        public void* dict;
+
+        public nuint dictSize;
+
+        public ZDICT_cover_params_t parameters;
+
+        public nuint compressedSize;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/COVER_dictSelection.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /**
+     * Struct used for the dictionary selection function.
+     */
+    public unsafe partial struct COVER_dictSelection
+    {
+        public byte* dictContent;
+
+        public nuint dictSize;
+
+        public nuint totalCompressedSize;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/COVER_epoch_info_t.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /**
+     *Number of epochs and size of each epoch.
+     */
+    public partial struct COVER_epoch_info_t
+    {
+        public uint num;
+
+        public uint size;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/COVER_segment_t.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /**
+     * A segment is a range in the source as well as the score of the segment.
+     */
+    public partial struct COVER_segment_t
+    {
+        public uint begin;
+
+        public uint end;
+
+        public uint score;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/Cover.cs

@@ -0,0 +1,411 @@
+using System;
+using static ZstdSharp.UnsafeHelper;
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        public static int g_displayLevel = 2;
+
+        /**
+         * Returns the sum of the sample sizes.
+         */
+        public static nuint COVER_sum(nuint* samplesSizes, uint nbSamples)
+        {
+            nuint sum = 0;
+            uint i;
+
+            for (i = 0; i < nbSamples; ++i)
+            {
+                sum += samplesSizes[i];
+            }
+
+            return sum;
+        }
+
+        /**
+         * Warns the user when their corpus is too small.
+         */
+        public static void COVER_warnOnSmallCorpus(nuint maxDictSize, nuint nbDmers, int displayLevel)
+        {
+            double ratio = (double)(nbDmers) / maxDictSize;
+
+            if (ratio >= 10)
+            {
+                return;
+            }
+
+            if (displayLevel >= 1)
+            {
+        ;
+            }
+
+        }
+
+        /**
+         * Computes the number of epochs and the size of each epoch.
+         * We will make sure that each epoch gets at least 10 * k bytes.
+         *
+         * The COVER algorithms divide the data up into epochs of equal size and
+         * select one segment from each epoch.
+         *
+         * @param maxDictSize The maximum allowed dictionary size.
+         * @param nbDmers     The number of dmers we are training on.
+         * @param k           The parameter k (segment size).
+         * @param passes      The target number of passes over the dmer corpus.
+         *                    More passes means a better dictionary.
+         */
+        public static COVER_epoch_info_t COVER_computeEpochs(uint maxDictSize, uint nbDmers, uint k, uint passes)
+        {
+            uint minEpochSize = k * 10;
+            COVER_epoch_info_t epochs;
+
+            epochs.num = (uint)((1) > (maxDictSize / k / passes) ? (1) : (maxDictSize / k / passes));
+            epochs.size = nbDmers / epochs.num;
+            if (epochs.size >= minEpochSize)
+            {
+                assert(epochs.size * epochs.num <= nbDmers);
+                return epochs;
+            }
+
+            epochs.size = ((minEpochSize) < (nbDmers) ? (minEpochSize) : (nbDmers));
+            epochs.num = nbDmers / epochs.size;
+            assert(epochs.size * epochs.num <= nbDmers);
+            return epochs;
+        }
+
+        /**
+         *  Checks total compressed size of a dictionary
+         */
+        public static nuint COVER_checkTotalCompressedSize(ZDICT_cover_params_t parameters, nuint* samplesSizes, byte* samples, nuint* offsets, nuint nbTrainSamples, nuint nbSamples, byte* dict, nuint dictBufferCapacity)
+        {
+            nuint totalCompressedSize = (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            ZSTD_CCtx_s* cctx;
+            ZSTD_CDict_s* cdict;
+            void* dst;
+            nuint dstCapacity;
+            nuint i;
+
+
+            {
+                nuint maxSampleSize = 0;
+
+                i = parameters.splitPoint < 1.0 ? nbTrainSamples : 0;
+                for (; i < nbSamples; ++i)
+                {
+                    maxSampleSize = ((samplesSizes[i]) > (maxSampleSize) ? (samplesSizes[i]) : (maxSampleSize));
+                }
+
+                dstCapacity = ZSTD_compressBound(maxSampleSize);
+                dst = malloc(dstCapacity);
+            }
+
+            cctx = ZSTD_createCCtx();
+            cdict = ZSTD_createCDict((void*)dict, dictBufferCapacity, parameters.zParams.compressionLevel);
+            if (dst == null || cctx == null || cdict == null)
+            {
+                goto _compressCleanup;
+            }
+
+            totalCompressedSize = dictBufferCapacity;
+            i = parameters.splitPoint < 1.0 ? nbTrainSamples : 0;
+            for (; i < nbSamples; ++i)
+            {
+                nuint size = ZSTD_compress_usingCDict(cctx, dst, dstCapacity, (void*)(samples + offsets[i]), samplesSizes[i], cdict);
+
+                if ((ERR_isError(size)) != 0)
+                {
+                    totalCompressedSize = size;
+                    goto _compressCleanup;
+                }
+
+                totalCompressedSize += size;
+            }
+
+            _compressCleanup:
+            ZSTD_freeCCtx(cctx);
+            ZSTD_freeCDict(cdict);
+            if (dst != null)
+            {
+                free(dst);
+            }
+
+            return totalCompressedSize;
+        }
+
+        /**
+         * Initialize the `COVER_best_t`.
+         */
+        public static void COVER_best_init(COVER_best_s* best)
+        {
+            if (best == null)
+            {
+                return;
+            }
+
+
+
+            best->liveJobs = 0;
+            best->dict = null;
+            best->dictSize = 0;
+            best->compressedSize = unchecked((nuint)(-1));
+            memset((void*)&best->parameters, 0, (nuint)(sizeof(ZDICT_cover_params_t)));
+        }
+
+        /**
+         * Wait until liveJobs == 0.
+         */
+        public static void COVER_best_wait(COVER_best_s* best)
+        {
+            if (best == null)
+            {
+                return;
+            }
+
+
+            while (best->liveJobs != 0)
+            {
+
+            }
+
+
+        }
+
+        /**
+         * Call COVER_best_wait() and then destroy the COVER_best_t.
+         */
+        public static void COVER_best_destroy(COVER_best_s* best)
+        {
+            if (best == null)
+            {
+                return;
+            }
+
+            COVER_best_wait(best);
+            if (best->dict != null)
+            {
+                free(best->dict);
+            }
+
+
+
+        }
+
+        /**
+         * Called when a thread is about to be launched.
+         * Increments liveJobs.
+         */
+        public static void COVER_best_start(COVER_best_s* best)
+        {
+            if (best == null)
+            {
+                return;
+            }
+
+
+            ++best->liveJobs;
+
+        }
+
+        /**
+         * Called when a thread finishes executing, both on error or success.
+         * Decrements liveJobs and signals any waiting threads if liveJobs == 0.
+         * If this dictionary is the best so far save it and its parameters.
+         */
+        public static void COVER_best_finish(COVER_best_s* best, ZDICT_cover_params_t parameters, COVER_dictSelection selection)
+        {
+            void* dict = (void*)selection.dictContent;
+            nuint compressedSize = selection.totalCompressedSize;
+            nuint dictSize = selection.dictSize;
+
+            if (best == null)
+            {
+                return;
+            }
+
+
+            {
+                nuint liveJobs;
+
+
+                --best->liveJobs;
+                liveJobs = best->liveJobs;
+                if (compressedSize < best->compressedSize)
+                {
+                    if (best->dict == null || best->dictSize < dictSize)
+                    {
+                        if (best->dict != null)
+                        {
+                            free(best->dict);
+                        }
+
+                        best->dict = malloc(dictSize);
+                        if (best->dict == null)
+                        {
+                            best->compressedSize = (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+                            best->dictSize = 0;
+
+
+                            return;
+                        }
+                    }
+
+                    if (dict != null)
+                    {
+                        memcpy(best->dict, dict, dictSize);
+                        best->dictSize = dictSize;
+                        best->parameters = parameters;
+                        best->compressedSize = compressedSize;
+                    }
+                }
+
+                if (liveJobs == 0)
+                {
+
+                }
+
+
+            }
+        }
+
+        /**
+          * Error function for COVER_selectDict function. Returns a struct where
+          * return.totalCompressedSize is a ZSTD error.
+          */
+        public static COVER_dictSelection COVER_dictSelectionError(nuint error)
+        {
+            COVER_dictSelection selection = new COVER_dictSelection
+            {
+                dictContent = null,
+                dictSize = 0,
+                totalCompressedSize = error,
+            };
+
+            return selection;
+        }
+
+        /**
+         * Error function for COVER_selectDict function. Checks if the return
+         * value is an error.
+         */
+        public static uint COVER_dictSelectionIsError(COVER_dictSelection selection)
+        {
+            return ((((ERR_isError(selection.totalCompressedSize)) != 0 || selection.dictContent == null)) ? 1U : 0U);
+        }
+
+        /**
+         * Always call after selectDict is called to free up used memory from
+         * newly created dictionary.
+         */
+        public static void COVER_dictSelectionFree(COVER_dictSelection selection)
+        {
+            free((void*)selection.dictContent);
+        }
+
+        /**
+         * Called to finalize the dictionary and select one based on whether or not
+         * the shrink-dict flag was enabled. If enabled the dictionary used is the
+         * smallest dictionary within a specified regression of the compressed size
+         * from the largest dictionary.
+         */
+        public static COVER_dictSelection COVER_selectDict(byte* customDictContent, nuint dictBufferCapacity, nuint dictContentSize, byte* samplesBuffer, nuint* samplesSizes, uint nbFinalizeSamples, nuint nbCheckSamples, nuint nbSamples, ZDICT_cover_params_t @params, nuint* offsets, nuint totalCompressedSize)
+        {
+            nuint largestDict = 0;
+            nuint largestCompressed = 0;
+            byte* customDictContentEnd = customDictContent + dictContentSize;
+            byte* largestDictbuffer = (byte*)(malloc(dictBufferCapacity));
+            byte* candidateDictBuffer = (byte*)(malloc(dictBufferCapacity));
+            double regressionTolerance = ((double)(@params.shrinkDictMaxRegression) / 100.0) + 1.00;
+
+            if (largestDictbuffer == null || candidateDictBuffer == null)
+            {
+                free((void*)largestDictbuffer);
+                free((void*)candidateDictBuffer);
+                return COVER_dictSelectionError(dictContentSize);
+            }
+
+            memcpy((void*)largestDictbuffer, (void*)customDictContent, dictContentSize);
+            dictContentSize = ZDICT_finalizeDictionary((void*)largestDictbuffer, dictBufferCapacity, (void*)customDictContent, dictContentSize, (void*)samplesBuffer, samplesSizes, nbFinalizeSamples, @params.zParams);
+            if ((ZDICT_isError(dictContentSize)) != 0)
+            {
+                free((void*)largestDictbuffer);
+                free((void*)candidateDictBuffer);
+                return COVER_dictSelectionError(dictContentSize);
+            }
+
+            totalCompressedSize = COVER_checkTotalCompressedSize(@params, samplesSizes, samplesBuffer, offsets, nbCheckSamples, nbSamples, largestDictbuffer, dictContentSize);
+            if ((ERR_isError(totalCompressedSize)) != 0)
+            {
+                free((void*)largestDictbuffer);
+                free((void*)candidateDictBuffer);
+                return COVER_dictSelectionError(totalCompressedSize);
+            }
+
+            if (@params.shrinkDict == 0)
+            {
+                COVER_dictSelection selection = new COVER_dictSelection
+                {
+                    dictContent = largestDictbuffer,
+                    dictSize = dictContentSize,
+                    totalCompressedSize = totalCompressedSize,
+                };
+
+                free((void*)candidateDictBuffer);
+                return selection;
+            }
+
+            largestDict = dictContentSize;
+            largestCompressed = totalCompressedSize;
+            dictContentSize = 256;
+            while (dictContentSize < largestDict)
+            {
+                memcpy((void*)candidateDictBuffer, (void*)largestDictbuffer, largestDict);
+                dictContentSize = ZDICT_finalizeDictionary((void*)candidateDictBuffer, dictBufferCapacity, (void*)(customDictContentEnd - dictContentSize), dictContentSize, (void*)samplesBuffer, samplesSizes, nbFinalizeSamples, @params.zParams);
+                if ((ZDICT_isError(dictContentSize)) != 0)
+                {
+                    free((void*)largestDictbuffer);
+                    free((void*)candidateDictBuffer);
+                    return COVER_dictSelectionError(dictContentSize);
+                }
+
+                totalCompressedSize = COVER_checkTotalCompressedSize(@params, samplesSizes, samplesBuffer, offsets, nbCheckSamples, nbSamples, candidateDictBuffer, dictContentSize);
+                if ((ERR_isError(totalCompressedSize)) != 0)
+                {
+                    free((void*)largestDictbuffer);
+                    free((void*)candidateDictBuffer);
+                    return COVER_dictSelectionError(totalCompressedSize);
+                }
+
+                if (totalCompressedSize <= largestCompressed * regressionTolerance)
+                {
+                    COVER_dictSelection selection = new COVER_dictSelection
+                    {
+                        dictContent = candidateDictBuffer,
+                        dictSize = dictContentSize,
+                        totalCompressedSize = totalCompressedSize,
+                    };
+
+                    free((void*)largestDictbuffer);
+                    return selection;
+                }
+
+                dictContentSize *= 2;
+            }
+
+            dictContentSize = largestDict;
+            totalCompressedSize = largestCompressed;
+
+            {
+                COVER_dictSelection selection = new COVER_dictSelection
+                {
+                    dictContent = largestDictbuffer,
+                    dictSize = dictContentSize,
+                    totalCompressedSize = totalCompressedSize,
+                };
+
+                free((void*)candidateDictBuffer);
+                return selection;
+            }
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/DTableDesc.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /*-***************************/
+    /*  generic DTableDesc       */
+    /*-***************************/
+    public partial struct DTableDesc
+    {
+        public byte maxTableLog;
+
+        public byte tableType;
+
+        public byte tableLog;
+
+        public byte reserved;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/EStats_ress_t.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public unsafe partial struct EStats_ress_t
+    {
+        /* dictionary */
+        public ZSTD_CDict_s* dict;
+
+        /* working context */
+        public ZSTD_CCtx_s* zc;
+
+        /* must be ZSTD_BLOCKSIZE_MAX allocated */
+        public void* workPlace;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/EntropyCommon.cs

@@ -0,0 +1,425 @@
+using System;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using static ZstdSharp.UnsafeHelper;
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        /*===   Version   ===*/
+        public static uint FSE_versionNumber()
+        {
+            return (uint)((0 * 100 * 100 + 9 * 100 + 0));
+        }
+
+        /*===   Error Management   ===*/
+        public static uint FSE_isError(nuint code)
+        {
+            return ERR_isError(code);
+        }
+
+        public static string FSE_getErrorName(nuint code)
+        {
+            return ERR_getErrorName(code);
+        }
+
+        /* Error Management */
+        public static uint HUF_isError(nuint code)
+        {
+            return ERR_isError(code);
+        }
+
+        public static string HUF_getErrorName(nuint code)
+        {
+            return ERR_getErrorName(code);
+        }
+
+        /*-**************************************************************
+        *  FSE NCount encoding-decoding
+        ****************************************************************/
+        [InlineMethod.Inline]
+        private static uint FSE_ctz(uint val)
+        {
+            assert(val != 0);
+
+            {
+                return (uint) BitOperations.TrailingZeroCount(val);
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint FSE_readNCount_body(short* normalizedCounter, uint* maxSVPtr, uint* tableLogPtr, void* headerBuffer, nuint hbSize)
+        {
+            byte* istart = (byte*)(headerBuffer);
+            byte* iend = istart + hbSize;
+            byte* ip = istart;
+            int nbBits;
+            int remaining;
+            int threshold;
+            uint bitStream;
+            int bitCount;
+            uint charnum = 0;
+            uint maxSV1 = *maxSVPtr + 1;
+            int previous0 = 0;
+
+            if (hbSize < 8)
+            {
+                sbyte* buffer = stackalloc sbyte[8];
+                memset(buffer, 0, sizeof(sbyte) * 8);
+
+                memcpy((void*)(buffer), (headerBuffer), (hbSize));
+
+                {
+                    nuint countSize = FSE_readNCount(normalizedCounter, maxSVPtr, tableLogPtr, (void*)buffer, (nuint)(8));
+
+                    if ((FSE_isError(countSize)) != 0)
+                    {
+                        return countSize;
+                    }
+
+                    if (countSize > hbSize)
+                    {
+                        return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_corruption_detected)));
+                    }
+
+                    return countSize;
+                }
+            }
+
+            assert(hbSize >= 8);
+            memset((void*)(normalizedCounter), (0), ((*maxSVPtr + 1) * (nuint)(sizeof(short))));
+            bitStream = MEM_readLE32((void*)ip);
+            nbBits = (int)((bitStream & 0xF) + 5);
+            if (nbBits > 15)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_tableLog_tooLarge)));
+            }
+
+            bitStream >>= 4;
+            bitCount = 4;
+            *tableLogPtr = (uint)nbBits;
+            remaining = (1 << nbBits) + 1;
+            threshold = 1 << nbBits;
+            nbBits++;
+            for (;;)
+            {
+                if (previous0 != 0)
+                {
+                    int repeats = (int)(FSE_ctz(~bitStream | 0x80000000) >> 1);
+
+                    while (repeats >= 12)
+                    {
+                        charnum += (uint)(3 * 12);
+                        if ((ip <= iend - 7))
+                        {
+                            ip += 3;
+                        }
+                        else
+                        {
+                            bitCount -= (int)(8 * (iend - 7 - ip));
+                            bitCount &= 31;
+                            ip = iend - 4;
+                        }
+
+                        bitStream = MEM_readLE32((void*)ip) >> bitCount;
+                        repeats = (int)(FSE_ctz(~bitStream | 0x80000000) >> 1);
+                    }
+
+                    charnum += (uint)(3 * repeats);
+                    bitStream >>= 2 * repeats;
+                    bitCount += 2 * repeats;
+                    assert((bitStream & 3) < 3);
+                    charnum += bitStream & 3;
+                    bitCount += 2;
+                    if (charnum >= maxSV1)
+                    {
+                        break;
+                    }
+
+                    if ((ip <= iend - 7) || (ip + (bitCount >> 3) <= iend - 4))
+                    {
+                        assert((bitCount >> 3) <= 3);
+                        ip += bitCount >> 3;
+                        bitCount &= 7;
+                    }
+                    else
+                    {
+                        bitCount -= (int)(8 * (iend - 4 - ip));
+                        bitCount &= 31;
+                        ip = iend - 4;
+                    }
+
+                    bitStream = MEM_readLE32((void*)ip) >> bitCount;
+                }
+
+
+                {
+                    int max = (2 * threshold - 1) - remaining;
+                    int count;
+
+                    if ((bitStream & (uint)((threshold - 1))) < (uint)(max))
+                    {
+                        count = (int)(bitStream & (uint)((threshold - 1)));
+                        bitCount += nbBits - 1;
+                    }
+                    else
+                    {
+                        count = (int)(bitStream & (uint)((2 * threshold - 1)));
+                        if (count >= threshold)
+                        {
+                            count -= max;
+                        }
+
+                        bitCount += nbBits;
+                    }
+
+                    count--;
+                    if (count >= 0)
+                    {
+                        remaining -= count;
+                    }
+                    else
+                    {
+                        assert(count == -1);
+                        remaining += count;
+                    }
+
+                    normalizedCounter[charnum++] = (short)(count);
+                    previous0 = (count == 0 ? 1 : 0);
+                    assert(threshold > 1);
+                    if (remaining < threshold)
+                    {
+                        if (remaining <= 1)
+                        {
+                            break;
+                        }
+
+                        nbBits = (int)(BIT_highbit32((uint)remaining) + 1);
+                        threshold = 1 << (nbBits - 1);
+                    }
+
+                    if (charnum >= maxSV1)
+                    {
+                        break;
+                    }
+
+                    if ((ip <= iend - 7) || (ip + (bitCount >> 3) <= iend - 4))
+                    {
+                        ip += bitCount >> 3;
+                        bitCount &= 7;
+                    }
+                    else
+                    {
+                        bitCount -= (int)(8 * (iend - 4 - ip));
+                        bitCount &= 31;
+                        ip = iend - 4;
+                    }
+
+                    bitStream = MEM_readLE32((void*)ip) >> bitCount;
+                }
+            }
+
+            if (remaining != 1)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_corruption_detected)));
+            }
+
+            if (charnum > maxSV1)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_maxSymbolValue_tooSmall)));
+            }
+
+            if (bitCount > 32)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_corruption_detected)));
+            }
+
+            *maxSVPtr = charnum - 1;
+            ip += (bitCount + 7) >> 3;
+            return (nuint)(ip - istart);
+        }
+
+        /* Avoids the FORCE_INLINE of the _body() function. */
+        private static nuint FSE_readNCount_body_default(short* normalizedCounter, uint* maxSVPtr, uint* tableLogPtr, void* headerBuffer, nuint hbSize)
+        {
+            return FSE_readNCount_body(normalizedCounter, maxSVPtr, tableLogPtr, headerBuffer, hbSize);
+        }
+
+        private static nuint FSE_readNCount_body_bmi2(short* normalizedCounter, uint* maxSVPtr, uint* tableLogPtr, void* headerBuffer, nuint hbSize)
+        {
+            return FSE_readNCount_body(normalizedCounter, maxSVPtr, tableLogPtr, headerBuffer, hbSize);
+        }
+
+        /*! FSE_readNCount_bmi2():
+         * Same as FSE_readNCount() but pass bmi2=1 when your CPU supports BMI2 and 0 otherwise.
+         */
+        public static nuint FSE_readNCount_bmi2(short* normalizedCounter, uint* maxSVPtr, uint* tableLogPtr, void* headerBuffer, nuint hbSize, int bmi2)
+        {
+            if (bmi2 != 0)
+            {
+                return FSE_readNCount_body_bmi2(normalizedCounter, maxSVPtr, tableLogPtr, headerBuffer, hbSize);
+            }
+
+            return FSE_readNCount_body_default(normalizedCounter, maxSVPtr, tableLogPtr, headerBuffer, hbSize);
+        }
+
+        /*! FSE_readNCount():
+            Read compactly saved 'normalizedCounter' from 'rBuffer'.
+            @return : size read from 'rBuffer',
+                      or an errorCode, which can be tested using FSE_isError().
+                      maxSymbolValuePtr[0] and tableLogPtr[0] will also be updated with their respective values */
+        public static nuint FSE_readNCount(short* normalizedCounter, uint* maxSVPtr, uint* tableLogPtr, void* headerBuffer, nuint hbSize)
+        {
+            return FSE_readNCount_bmi2(normalizedCounter, maxSVPtr, tableLogPtr, headerBuffer, hbSize, 0);
+        }
+
+        /*! HUF_readStats() :
+            Read compact Huffman tree, saved by HUF_writeCTable().
+            `huffWeight` is destination buffer.
+            `rankStats` is assumed to be a table of at least HUF_TABLELOG_MAX U32.
+            @return : size read from `src` , or an error Code .
+            Note : Needed by HUF_readCTable() and HUF_readDTableX?() .
+        */
+        public static nuint HUF_readStats(byte* huffWeight, nuint hwSize, uint* rankStats, uint* nbSymbolsPtr, uint* tableLogPtr, void* src, nuint srcSize)
+        {
+            uint* wksp = stackalloc uint[218];
+
+            return HUF_readStats_wksp(huffWeight, hwSize, rankStats, nbSymbolsPtr, tableLogPtr, src, srcSize, (void*)wksp, (nuint)(sizeof(uint) * 218), 0);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint HUF_readStats_body(byte* huffWeight, nuint hwSize, uint* rankStats, uint* nbSymbolsPtr, uint* tableLogPtr, void* src, nuint srcSize, void* workSpace, nuint wkspSize, int bmi2)
+        {
+            uint weightTotal;
+            byte* ip = (byte*)(src);
+            nuint iSize;
+            nuint oSize;
+
+            if (srcSize == 0)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_srcSize_wrong)));
+            }
+
+            iSize = ip[0];
+            if (iSize >= 128)
+            {
+                oSize = iSize - 127;
+                iSize = ((oSize + 1) / 2);
+                if (iSize + 1 > srcSize)
+                {
+                    return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_srcSize_wrong)));
+                }
+
+                if (oSize >= hwSize)
+                {
+                    return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_corruption_detected)));
+                }
+
+                ip += 1;
+
+                {
+                    uint n;
+
+                    for (n = 0; n < oSize; n += 2)
+                    {
+                        huffWeight[n] = (byte)(ip[n / 2] >> 4);
+                        huffWeight[n + 1] = (byte)(ip[n / 2] & 15);
+                    }
+                }
+            }
+            else
+            {
+                if (iSize + 1 > srcSize)
+                {
+                    return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_srcSize_wrong)));
+                }
+
+                oSize = FSE_decompress_wksp_bmi2((void*)huffWeight, hwSize - 1, (void*)(ip + 1), iSize, 6, workSpace, wkspSize, bmi2);
+                if ((FSE_isError(oSize)) != 0)
+                {
+                    return oSize;
+                }
+            }
+
+            memset((void*)(rankStats), (0), ((uint)((12 + 1)) * (nuint)(sizeof(uint))));
+            weightTotal = 0;
+
+            {
+                uint n;
+
+                for (n = 0; n < oSize; n++)
+                {
+                    if (huffWeight[n] >= 12)
+                    {
+                        return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_corruption_detected)));
+                    }
+
+                    rankStats[huffWeight[n]]++;
+                    weightTotal += (uint)((1 << (int)(huffWeight[n])) >> 1);
+                }
+            }
+
+            if (weightTotal == 0)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_corruption_detected)));
+            }
+
+
+            {
+                uint tableLog = BIT_highbit32(weightTotal) + 1;
+
+                if (tableLog > 12)
+                {
+                    return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_corruption_detected)));
+                }
+
+                *tableLogPtr = tableLog;
+
+                {
+                    uint total = (uint)(1 << (int)tableLog);
+                    uint rest = total - weightTotal;
+                    uint verif = (uint)(1 << (int)(BIT_highbit32(rest)));
+                    uint lastWeight = BIT_highbit32(rest) + 1;
+
+                    if (verif != rest)
+                    {
+                        return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_corruption_detected)));
+                    }
+
+                    huffWeight[oSize] = (byte)(lastWeight);
+                    rankStats[lastWeight]++;
+                }
+            }
+
+            if ((rankStats[1] < 2) || (rankStats[1] & 1) != 0)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_corruption_detected)));
+            }
+
+            *nbSymbolsPtr = (uint)(oSize + 1);
+            return iSize + 1;
+        }
+
+        /* Avoids the FORCE_INLINE of the _body() function. */
+        private static nuint HUF_readStats_body_default(byte* huffWeight, nuint hwSize, uint* rankStats, uint* nbSymbolsPtr, uint* tableLogPtr, void* src, nuint srcSize, void* workSpace, nuint wkspSize)
+        {
+            return HUF_readStats_body(huffWeight, hwSize, rankStats, nbSymbolsPtr, tableLogPtr, src, srcSize, workSpace, wkspSize, 0);
+        }
+
+        private static nuint HUF_readStats_body_bmi2(byte* huffWeight, nuint hwSize, uint* rankStats, uint* nbSymbolsPtr, uint* tableLogPtr, void* src, nuint srcSize, void* workSpace, nuint wkspSize)
+        {
+            return HUF_readStats_body(huffWeight, hwSize, rankStats, nbSymbolsPtr, tableLogPtr, src, srcSize, workSpace, wkspSize, 1);
+        }
+
+        public static nuint HUF_readStats_wksp(byte* huffWeight, nuint hwSize, uint* rankStats, uint* nbSymbolsPtr, uint* tableLogPtr, void* src, nuint srcSize, void* workSpace, nuint wkspSize, int bmi2)
+        {
+            if (bmi2 != 0)
+            {
+                return HUF_readStats_body_bmi2(huffWeight, hwSize, rankStats, nbSymbolsPtr, tableLogPtr, src, srcSize, workSpace, wkspSize);
+            }
+
+            return HUF_readStats_body_default(huffWeight, hwSize, rankStats, nbSymbolsPtr, tableLogPtr, src, srcSize, workSpace, wkspSize);
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/ErrorPrivate.cs

@@ -0,0 +1,184 @@
+using System;
+using System.Runtime.CompilerServices;
+using static ZstdSharp.UnsafeHelper;
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static uint ERR_isError(nuint code)
+        {
+            return (((code > (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_maxCode))))) ? 1U : 0U);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static ZSTD_ErrorCode ERR_getErrorCode(nuint code)
+        {
+            if ((ERR_isError(code)) == 0)
+            {
+                return (ZSTD_ErrorCode)(0);
+            }
+
+            return (ZSTD_ErrorCode)(0 - code);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static string ERR_getErrorName(nuint code)
+        {
+            return ERR_getErrorString(ERR_getErrorCode(code));
+        }
+
+        /*-****************************************
+        *  Error Strings
+        ******************************************/
+        public static string ERR_getErrorString(ZSTD_ErrorCode code)
+        {
+            var notErrorCode = "Unspecified error code";
+
+            switch (code)
+            {
+                case ZSTD_ErrorCode.ZSTD_error_no_error:
+                {
+                    return "No error detected";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_GENERIC:
+                {
+                    return "Error (generic)";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_prefix_unknown:
+                {
+                    return "Unknown frame descriptor";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_version_unsupported:
+                {
+                    return "Version not supported";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_frameParameter_unsupported:
+                {
+                    return "Unsupported frame parameter";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_frameParameter_windowTooLarge:
+                {
+                    return "Frame requires too much memory for decoding";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_corruption_detected:
+                {
+                    return "Corrupted block detected";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_checksum_wrong:
+                {
+                    return "Restored data doesn't match checksum";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_parameter_unsupported:
+                {
+                    return "Unsupported parameter";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_parameter_outOfBound:
+                {
+                    return "Parameter is out of bound";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_init_missing:
+                {
+                    return "Context should be init first";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_memory_allocation:
+                {
+                    return "Allocation error : not enough memory";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_workSpace_tooSmall:
+                {
+                    return "workSpace buffer is not large enough";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_stage_wrong:
+                {
+                    return "Operation not authorized at current processing stage";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_tableLog_tooLarge:
+                {
+                    return "tableLog requires too much memory : unsupported";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_maxSymbolValue_tooLarge:
+                {
+                    return "Unsupported max Symbol Value : too large";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_maxSymbolValue_tooSmall:
+                {
+                    return "Specified maxSymbolValue is too small";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_dictionary_corrupted:
+                {
+                    return "Dictionary is corrupted";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_dictionary_wrong:
+                {
+                    return "Dictionary mismatch";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_dictionaryCreation_failed:
+                {
+                    return "Cannot create Dictionary from provided samples";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall:
+                {
+                    return "Destination buffer is too small";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_srcSize_wrong:
+                {
+                    return "Src size is incorrect";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_dstBuffer_null:
+                {
+                    return "Operation on NULL destination buffer";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_frameIndex_tooLarge:
+                {
+                    return "Frame index is too large";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_seekableIO:
+                {
+                    return "An I/O error occurred when reading/seeking";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_dstBuffer_wrong:
+                {
+                    return "Destination buffer is wrong";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_srcBuffer_wrong:
+                {
+                    return "Source buffer is wrong";
+                }
+
+                case ZSTD_ErrorCode.ZSTD_error_maxCode:
+                default:
+                {
+                    return notErrorCode;
+                }
+            }
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FASTCOVER_accel_t.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /*-*************************************
+    * Acceleration
+    ***************************************/
+    public partial struct FASTCOVER_accel_t
+    {
+        /* Percentage of training samples used for ZDICT_finalizeDictionary */
+        public uint finalize;
+
+        /* Number of dmer skipped between each dmer counted in computeFrequency */
+        public uint skip;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FASTCOVER_ctx_t.cs

@@ -0,0 +1,32 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /*-*************************************
+    * Context
+    ***************************************/
+    public unsafe partial struct FASTCOVER_ctx_t
+    {
+        public byte* samples;
+
+        public nuint* offsets;
+
+        public nuint* samplesSizes;
+
+        public nuint nbSamples;
+
+        public nuint nbTrainSamples;
+
+        public nuint nbTestSamples;
+
+        public nuint nbDmers;
+
+        public uint* freqs;
+
+        public uint d;
+
+        public uint f;
+
+        public FASTCOVER_accel_t accelParams;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FASTCOVER_tryParameters_data_s.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /**
+     * Parameters for FASTCOVER_tryParameters().
+     */
+    public unsafe partial struct FASTCOVER_tryParameters_data_s
+    {
+        public FASTCOVER_ctx_t* ctx;
+
+        public COVER_best_s* best;
+
+        public nuint dictBufferCapacity;
+
+        public ZDICT_cover_params_t parameters;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FSE_CState_t.cs

@@ -0,0 +1,22 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /* *****************************************
+    *  FSE symbol compression API
+    *******************************************/
+    /*!
+       This API consists of small unitary functions, which highly benefit from being inlined.
+       Hence their body are included in next section.
+    */
+    public unsafe partial struct FSE_CState_t
+    {
+        public nint value;
+
+        public void* stateTable;
+
+        public void* symbolTT;
+
+        public uint stateLog;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FSE_DState_t.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /* *****************************************
+    *  FSE symbol decompression API
+    *******************************************/
+    public unsafe partial struct FSE_DState_t
+    {
+        public nuint state;
+
+        /* precise table may vary, depending on U16 */
+        public void* table;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FSE_DTableHeader.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /* ======    Decompression    ====== */
+    public partial struct FSE_DTableHeader
+    {
+        public ushort tableLog;
+
+        public ushort fastMode;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FSE_DecompressWksp.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public unsafe partial struct FSE_DecompressWksp
+    {
+        public fixed short ncount[256];
+
+        /* Dynamically sized */
+        public fixed uint dtable[1];
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FSE_decode_t.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public partial struct FSE_decode_t
+    {
+        public ushort newState;
+
+        public byte symbol;
+
+        public byte nbBits;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FSE_repeat.cs

@@ -0,0 +1,11 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public enum FSE_repeat
+    {
+        FSE_repeat_none,
+        FSE_repeat_check,
+        FSE_repeat_valid,
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FSE_symbolCompressionTransform.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /* *****************************************
+    *  Implementation of inlined functions
+    *******************************************/
+    public partial struct FSE_symbolCompressionTransform
+    {
+        public int deltaFindState;
+
+        public uint deltaNbBits;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/Fastcover.cs

@@ -0,0 +1,715 @@
+using System;
+using static ZstdSharp.UnsafeHelper;
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        /*-*************************************
+        * Hash Functions
+        ***************************************/
+        /**
+         * Hash the d-byte value pointed to by p and mod 2^f into the frequency vector
+         */
+        private static nuint FASTCOVER_hashPtrToIndex(void* p, uint f, uint d)
+        {
+            if (d == 6)
+            {
+                return ZSTD_hash6Ptr(p, f);
+            }
+
+            return ZSTD_hash8Ptr(p, f);
+        }
+
+        public static FASTCOVER_accel_t* FASTCOVER_defaultAccelParameters = GetArrayPointer(new FASTCOVER_accel_t[11]
+        {
+            new FASTCOVER_accel_t
+            {
+                finalize = 100,
+                skip = 0,
+            },
+            new FASTCOVER_accel_t
+            {
+                finalize = 100,
+                skip = 0,
+            },
+            new FASTCOVER_accel_t
+            {
+                finalize = 50,
+                skip = 1,
+            },
+            new FASTCOVER_accel_t
+            {
+                finalize = 34,
+                skip = 2,
+            },
+            new FASTCOVER_accel_t
+            {
+                finalize = 25,
+                skip = 3,
+            },
+            new FASTCOVER_accel_t
+            {
+                finalize = 20,
+                skip = 4,
+            },
+            new FASTCOVER_accel_t
+            {
+                finalize = 17,
+                skip = 5,
+            },
+            new FASTCOVER_accel_t
+            {
+                finalize = 14,
+                skip = 6,
+            },
+            new FASTCOVER_accel_t
+            {
+                finalize = 13,
+                skip = 7,
+            },
+            new FASTCOVER_accel_t
+            {
+                finalize = 11,
+                skip = 8,
+            },
+            new FASTCOVER_accel_t
+            {
+                finalize = 10,
+                skip = 9,
+            },
+        });
+
+        /*-*************************************
+        *  Helper functions
+        ***************************************/
+        /**
+         * Selects the best segment in an epoch.
+         * Segments of are scored according to the function:
+         *
+         * Let F(d) be the frequency of all dmers with hash value d.
+         * Let S_i be hash value of the dmer at position i of segment S which has length k.
+         *
+         *     Score(S) = F(S_1) + F(S_2) + ... + F(S_{k-d+1})
+         *
+         * Once the dmer with hash value d is in the dictionary we set F(d) = 0.
+         */
+        private static COVER_segment_t FASTCOVER_selectSegment(FASTCOVER_ctx_t* ctx, uint* freqs, uint begin, uint end, ZDICT_cover_params_t parameters, ushort* segmentFreqs)
+        {
+            uint k = parameters.k;
+            uint d = parameters.d;
+            uint f = ctx->f;
+            uint dmersInK = k - d + 1;
+            COVER_segment_t bestSegment = new COVER_segment_t
+            {
+                begin = 0,
+                end = 0,
+                score = 0,
+            };
+            COVER_segment_t activeSegment;
+
+            activeSegment.begin = begin;
+            activeSegment.end = begin;
+            activeSegment.score = 0;
+            while (activeSegment.end < end)
+            {
+                nuint idx = FASTCOVER_hashPtrToIndex((void*)(ctx->samples + activeSegment.end), f, d);
+
+                if (segmentFreqs[idx] == 0)
+                {
+                    activeSegment.score += freqs[idx];
+                }
+
+                activeSegment.end += 1;
+                segmentFreqs[idx] += 1;
+                if (activeSegment.end - activeSegment.begin == dmersInK + 1)
+                {
+                    nuint delIndex = FASTCOVER_hashPtrToIndex((void*)(ctx->samples + activeSegment.begin), f, d);
+
+                    segmentFreqs[delIndex] -= 1;
+                    if (segmentFreqs[delIndex] == 0)
+                    {
+                        activeSegment.score -= freqs[delIndex];
+                    }
+
+                    activeSegment.begin += 1;
+                }
+
+                if (activeSegment.score > bestSegment.score)
+                {
+                    bestSegment = activeSegment;
+                }
+            }
+
+            while (activeSegment.begin < end)
+            {
+                nuint delIndex = FASTCOVER_hashPtrToIndex((void*)(ctx->samples + activeSegment.begin), f, d);
+
+                segmentFreqs[delIndex] -= 1;
+                activeSegment.begin += 1;
+            }
+
+
+            {
+                uint pos;
+
+                for (pos = bestSegment.begin; pos != bestSegment.end; ++pos)
+                {
+                    nuint i = FASTCOVER_hashPtrToIndex((void*)(ctx->samples + pos), f, d);
+
+                    freqs[i] = 0;
+                }
+            }
+
+            return bestSegment;
+        }
+
+        private static int FASTCOVER_checkParameters(ZDICT_cover_params_t parameters, nuint maxDictSize, uint f, uint accel)
+        {
+            if (parameters.d == 0 || parameters.k == 0)
+            {
+                return 0;
+            }
+
+            if (parameters.d != 6 && parameters.d != 8)
+            {
+                return 0;
+            }
+
+            if (parameters.k > maxDictSize)
+            {
+                return 0;
+            }
+
+            if (parameters.d > parameters.k)
+            {
+                return 0;
+            }
+
+            if (f > 31 || f == 0)
+            {
+                return 0;
+            }
+
+            if (parameters.splitPoint <= 0 || parameters.splitPoint > 1)
+            {
+                return 0;
+            }
+
+            if (accel > 10 || accel == 0)
+            {
+                return 0;
+            }
+
+            return 1;
+        }
+
+        /**
+         * Clean up a context initialized with `FASTCOVER_ctx_init()`.
+         */
+        private static void FASTCOVER_ctx_destroy(FASTCOVER_ctx_t* ctx)
+        {
+            if (ctx == null)
+            {
+                return;
+            }
+
+            free((void*)ctx->freqs);
+            ctx->freqs = null;
+            free((void*)ctx->offsets);
+            ctx->offsets = null;
+        }
+
+        /**
+         * Calculate for frequency of hash value of each dmer in ctx->samples
+         */
+        private static void FASTCOVER_computeFrequency(uint* freqs, FASTCOVER_ctx_t* ctx)
+        {
+            uint f = ctx->f;
+            uint d = ctx->d;
+            uint skip = ctx->accelParams.skip;
+            uint readLength = ((d) > (8) ? (d) : (8));
+            nuint i;
+
+            assert(ctx->nbTrainSamples >= 5);
+            assert(ctx->nbTrainSamples <= ctx->nbSamples);
+            for (i = 0; i < ctx->nbTrainSamples; i++)
+            {
+                nuint start = ctx->offsets[i];
+                nuint currSampleEnd = ctx->offsets[i + 1];
+
+                while (start + readLength <= currSampleEnd)
+                {
+                    nuint dmerIndex = FASTCOVER_hashPtrToIndex((void*)(ctx->samples + start), f, d);
+
+                    freqs[dmerIndex]++;
+                    start = start + skip + 1;
+                }
+            }
+        }
+
+        /**
+         * Prepare a context for dictionary building.
+         * The context is only dependent on the parameter `d` and can used multiple
+         * times.
+         * Returns 0 on success or error code on error.
+         * The context must be destroyed with `FASTCOVER_ctx_destroy()`.
+         */
+        private static nuint FASTCOVER_ctx_init(FASTCOVER_ctx_t* ctx, void* samplesBuffer, nuint* samplesSizes, uint nbSamples, uint d, double splitPoint, uint f, FASTCOVER_accel_t accelParams)
+        {
+            byte* samples = (byte*)(samplesBuffer);
+            nuint totalSamplesSize = COVER_sum(samplesSizes, nbSamples);
+            uint nbTrainSamples = splitPoint < 1.0 ? (uint)((double)(nbSamples) * splitPoint) : nbSamples;
+            uint nbTestSamples = splitPoint < 1.0 ? nbSamples - nbTrainSamples : nbSamples;
+            nuint trainingSamplesSize = splitPoint < 1.0 ? COVER_sum(samplesSizes, nbTrainSamples) : totalSamplesSize;
+            nuint testSamplesSize = splitPoint < 1.0 ? COVER_sum(samplesSizes + nbTrainSamples, nbTestSamples) : totalSamplesSize;
+
+            if (totalSamplesSize < ((d) > ((nuint)(sizeof(ulong))) ? (d) : ((nuint)(sizeof(ulong)))) || totalSamplesSize >= (nuint)((nuint)(sizeof(nuint)) == 8 ? (unchecked((uint)(-1))) : ((uint)(1) * (1U << 30))))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_srcSize_wrong)));
+            }
+
+            if (nbTrainSamples < 5)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_srcSize_wrong)));
+            }
+
+            if (nbTestSamples < 1)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_srcSize_wrong)));
+            }
+
+            memset((void*)ctx, 0, (nuint)(sizeof(FASTCOVER_ctx_t)));
+            ctx->samples = samples;
+            ctx->samplesSizes = samplesSizes;
+            ctx->nbSamples = nbSamples;
+            ctx->nbTrainSamples = nbTrainSamples;
+            ctx->nbTestSamples = nbTestSamples;
+            ctx->nbDmers = trainingSamplesSize - ((d) > ((nuint)(sizeof(ulong))) ? (d) : ((nuint)(sizeof(ulong)))) + 1;
+            ctx->d = d;
+            ctx->f = f;
+            ctx->accelParams = accelParams;
+            ctx->offsets = (nuint*)(calloc((nbSamples + 1), (nuint)(sizeof(nuint))));
+            if (ctx->offsets == null)
+            {
+                FASTCOVER_ctx_destroy(ctx);
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_memory_allocation)));
+            }
+
+
+            {
+                uint i;
+
+                ctx->offsets[0] = 0;
+                assert(nbSamples >= 5);
+                for (i = 1; i <= nbSamples; ++i)
+                {
+                    ctx->offsets[i] = ctx->offsets[i - 1] + samplesSizes[i - 1];
+                }
+            }
+
+            ctx->freqs = (uint*)(calloc((nuint)((ulong)(1) << (int)f), (nuint)(sizeof(uint))));
+            if (ctx->freqs == null)
+            {
+                FASTCOVER_ctx_destroy(ctx);
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_memory_allocation)));
+            }
+
+            FASTCOVER_computeFrequency(ctx->freqs, ctx);
+            return 0;
+        }
+
+        /**
+         * Given the prepared context build the dictionary.
+         */
+        private static nuint FASTCOVER_buildDictionary(FASTCOVER_ctx_t* ctx, uint* freqs, void* dictBuffer, nuint dictBufferCapacity, ZDICT_cover_params_t parameters, ushort* segmentFreqs)
+        {
+            byte* dict = (byte*)(dictBuffer);
+            nuint tail = dictBufferCapacity;
+            COVER_epoch_info_t epochs = COVER_computeEpochs((uint)(dictBufferCapacity), (uint)(ctx->nbDmers), parameters.k, 1);
+            nuint maxZeroScoreRun = 10;
+            nuint zeroScoreRun = 0;
+            nuint epoch;
+
+            for (epoch = 0; tail > 0; epoch = (nuint)((epoch + 1) % epochs.num))
+            {
+                uint epochBegin = (uint)(epoch * epochs.size);
+                uint epochEnd = epochBegin + epochs.size;
+                nuint segmentSize;
+                COVER_segment_t segment = FASTCOVER_selectSegment(ctx, freqs, epochBegin, epochEnd, parameters, segmentFreqs);
+
+                if (segment.score == 0)
+                {
+                    if (++zeroScoreRun >= maxZeroScoreRun)
+                    {
+                        break;
+                    }
+
+                    continue;
+                }
+
+                zeroScoreRun = 0;
+                segmentSize = ((segment.end - segment.begin + parameters.d - 1) < (tail) ? (segment.end - segment.begin + parameters.d - 1) : (tail));
+                if (segmentSize < parameters.d)
+                {
+                    break;
+                }
+
+                tail -= segmentSize;
+                memcpy((void*)(dict + tail), (void*)(ctx->samples + segment.begin), segmentSize);
+            }
+
+            return tail;
+        }
+
+        /**
+         * Tries a set of parameters and updates the COVER_best_t with the results.
+         * This function is thread safe if zstd is compiled with multithreaded support.
+         * It takes its parameters as an *OWNING* opaque pointer to support threading.
+         */
+        private static void FASTCOVER_tryParameters(void* opaque)
+        {
+            FASTCOVER_tryParameters_data_s* data = (FASTCOVER_tryParameters_data_s*)(opaque);
+            FASTCOVER_ctx_t* ctx = data->ctx;
+            ZDICT_cover_params_t parameters = data->parameters;
+            nuint dictBufferCapacity = data->dictBufferCapacity;
+            nuint totalCompressedSize = (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            ushort* segmentFreqs = (ushort*)(calloc((nuint)((ulong)(1) << (int)ctx->f), (nuint)(2)));
+            byte* dict = (byte*)(malloc(dictBufferCapacity));
+            COVER_dictSelection selection = COVER_dictSelectionError((unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC))));
+            uint* freqs = (uint*)(malloc((nuint)(((ulong)(1) << (int)ctx->f) * (nuint)(4))));
+
+            if (segmentFreqs == null || dict == null || freqs == null)
+            {
+                goto _cleanup;
+            }
+
+            memcpy((void*)freqs, (void*)ctx->freqs, (nuint)(((ulong)(1) << (int)ctx->f) * (nuint)(sizeof(uint))));
+
+            {
+                nuint tail = FASTCOVER_buildDictionary(ctx, freqs, (void*)dict, dictBufferCapacity, parameters, segmentFreqs);
+                uint nbFinalizeSamples = (uint)(ctx->nbTrainSamples * ctx->accelParams.finalize / 100);
+
+                selection = COVER_selectDict(dict + tail, dictBufferCapacity, dictBufferCapacity - tail, ctx->samples, ctx->samplesSizes, nbFinalizeSamples, ctx->nbTrainSamples, ctx->nbSamples, parameters, ctx->offsets, totalCompressedSize);
+                if ((COVER_dictSelectionIsError(selection)) != 0)
+                {
+                    goto _cleanup;
+                }
+            }
+
+            _cleanup:
+            free((void*)dict);
+            COVER_best_finish(data->best, parameters, selection);
+            free((void*)data);
+            free((void*)segmentFreqs);
+            COVER_dictSelectionFree(selection);
+            free((void*)freqs);
+        }
+
+        private static void FASTCOVER_convertToCoverParams(ZDICT_fastCover_params_t fastCoverParams, ZDICT_cover_params_t* coverParams)
+        {
+            coverParams->k = fastCoverParams.k;
+            coverParams->d = fastCoverParams.d;
+            coverParams->steps = fastCoverParams.steps;
+            coverParams->nbThreads = fastCoverParams.nbThreads;
+            coverParams->splitPoint = fastCoverParams.splitPoint;
+            coverParams->zParams = fastCoverParams.zParams;
+            coverParams->shrinkDict = fastCoverParams.shrinkDict;
+        }
+
+        private static void FASTCOVER_convertToFastCoverParams(ZDICT_cover_params_t coverParams, ZDICT_fastCover_params_t* fastCoverParams, uint f, uint accel)
+        {
+            fastCoverParams->k = coverParams.k;
+            fastCoverParams->d = coverParams.d;
+            fastCoverParams->steps = coverParams.steps;
+            fastCoverParams->nbThreads = coverParams.nbThreads;
+            fastCoverParams->splitPoint = coverParams.splitPoint;
+            fastCoverParams->f = f;
+            fastCoverParams->accel = accel;
+            fastCoverParams->zParams = coverParams.zParams;
+            fastCoverParams->shrinkDict = coverParams.shrinkDict;
+        }
+
+        /*! ZDICT_trainFromBuffer_fastCover():
+         *  Train a dictionary from an array of samples using a modified version of COVER algorithm.
+         *  Samples must be stored concatenated in a single flat buffer `samplesBuffer`,
+         *  supplied with an array of sizes `samplesSizes`, providing the size of each sample, in order.
+         *  d and k are required.
+         *  All other parameters are optional, will use default values if not provided
+         *  The resulting dictionary will be saved into `dictBuffer`.
+         * @return: size of dictionary stored into `dictBuffer` (<= `dictBufferCapacity`)
+         *          or an error code, which can be tested with ZDICT_isError().
+         *          See ZDICT_trainFromBuffer() for details on failure modes.
+         *  Note: ZDICT_trainFromBuffer_fastCover() requires 6 * 2^f bytes of memory.
+         *  Tips: In general, a reasonable dictionary has a size of ~ 100 KB.
+         *        It's possible to select smaller or larger size, just by specifying `dictBufferCapacity`.
+         *        In general, it's recommended to provide a few thousands samples, though this can vary a lot.
+         *        It's recommended that total size of all samples be about ~x100 times the target size of dictionary.
+         */
+        public static nuint ZDICT_trainFromBuffer_fastCover(void* dictBuffer, nuint dictBufferCapacity, void* samplesBuffer, nuint* samplesSizes, uint nbSamples, ZDICT_fastCover_params_t parameters)
+        {
+            byte* dict = (byte*)(dictBuffer);
+            FASTCOVER_ctx_t ctx;
+            ZDICT_cover_params_t coverParams;
+            FASTCOVER_accel_t accelParams;
+
+            g_displayLevel = (int)parameters.zParams.notificationLevel;
+            parameters.splitPoint = 1.0;
+            parameters.f = (uint)(parameters.f == 0 ? 20 : parameters.f);
+            parameters.accel = (uint)(parameters.accel == 0 ? 1 : parameters.accel);
+            memset((void*)&coverParams, 0, (nuint)(sizeof(ZDICT_cover_params_t)));
+            FASTCOVER_convertToCoverParams(parameters, &coverParams);
+            if ((FASTCOVER_checkParameters(coverParams, dictBufferCapacity, parameters.f, parameters.accel)) == 0)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_parameter_outOfBound)));
+            }
+
+            if (nbSamples == 0)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_srcSize_wrong)));
+            }
+
+            if (dictBufferCapacity < 256)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall)));
+            }
+
+            accelParams = FASTCOVER_defaultAccelParameters[parameters.accel];
+
+            {
+                nuint initVal = FASTCOVER_ctx_init(&ctx, samplesBuffer, samplesSizes, nbSamples, coverParams.d, parameters.splitPoint, parameters.f, accelParams);
+
+                if ((ERR_isError(initVal)) != 0)
+                {
+                    return initVal;
+                }
+            }
+
+            COVER_warnOnSmallCorpus(dictBufferCapacity, ctx.nbDmers, g_displayLevel);
+
+            {
+                ushort* segmentFreqs = (ushort*)(calloc((nuint)((ulong)(1) << (int)parameters.f), (nuint)(2)));
+                nuint tail = FASTCOVER_buildDictionary(&ctx, ctx.freqs, dictBuffer, dictBufferCapacity, coverParams, segmentFreqs);
+                uint nbFinalizeSamples = (uint)(ctx.nbTrainSamples * ctx.accelParams.finalize / 100);
+                nuint dictionarySize = ZDICT_finalizeDictionary((void*)dict, dictBufferCapacity, (void*)(dict + tail), dictBufferCapacity - tail, samplesBuffer, samplesSizes, nbFinalizeSamples, coverParams.zParams);
+
+                if ((ERR_isError(dictionarySize)) == 0)
+                {
+        ;
+                }
+
+                FASTCOVER_ctx_destroy(&ctx);
+                free((void*)segmentFreqs);
+                return dictionarySize;
+            }
+        }
+
+        /*! ZDICT_optimizeTrainFromBuffer_fastCover():
+         * The same requirements as above hold for all the parameters except `parameters`.
+         * This function tries many parameter combinations (specifically, k and d combinations)
+         * and picks the best parameters. `*parameters` is filled with the best parameters found,
+         * dictionary constructed with those parameters is stored in `dictBuffer`.
+         * All of the parameters d, k, steps, f, and accel are optional.
+         * If d is non-zero then we don't check multiple values of d, otherwise we check d = {6, 8}.
+         * if steps is zero it defaults to its default value.
+         * If k is non-zero then we don't check multiple values of k, otherwise we check steps values in [50, 2000].
+         * If f is zero, default value of 20 is used.
+         * If accel is zero, default value of 1 is used.
+         *
+         * @return: size of dictionary stored into `dictBuffer` (<= `dictBufferCapacity`)
+         *          or an error code, which can be tested with ZDICT_isError().
+         *          On success `*parameters` contains the parameters selected.
+         *          See ZDICT_trainFromBuffer() for details on failure modes.
+         * Note: ZDICT_optimizeTrainFromBuffer_fastCover() requires about 6 * 2^f bytes of memory for each thread.
+         */
+        public static nuint ZDICT_optimizeTrainFromBuffer_fastCover(void* dictBuffer, nuint dictBufferCapacity, void* samplesBuffer, nuint* samplesSizes, uint nbSamples, ZDICT_fastCover_params_t* parameters)
+        {
+            ZDICT_cover_params_t coverParams;
+            FASTCOVER_accel_t accelParams;
+            uint nbThreads = parameters->nbThreads;
+            double splitPoint = parameters->splitPoint <= 0.0 ? 0.75 : parameters->splitPoint;
+            uint kMinD = (uint)(parameters->d == 0 ? 6 : parameters->d);
+            uint kMaxD = (uint)(parameters->d == 0 ? 8 : parameters->d);
+            uint kMinK = (uint)(parameters->k == 0 ? 50 : parameters->k);
+            uint kMaxK = (uint)(parameters->k == 0 ? 2000 : parameters->k);
+            uint kSteps = (uint)(parameters->steps == 0 ? 40 : parameters->steps);
+            uint kStepSize = (((kMaxK - kMinK) / kSteps) > (1) ? ((kMaxK - kMinK) / kSteps) : (1));
+            uint kIterations = (1 + (kMaxD - kMinD) / 2) * (1 + (kMaxK - kMinK) / kStepSize);
+            uint f = (uint)(parameters->f == 0 ? 20 : parameters->f);
+            uint accel = (uint)(parameters->accel == 0 ? 1 : parameters->accel);
+            uint shrinkDict = 0;
+            int displayLevel = (int)parameters->zParams.notificationLevel;
+            uint iteration = 1;
+            uint d;
+            uint k;
+            COVER_best_s best;
+            int warned = 0;
+
+            if (splitPoint <= 0 || splitPoint > 1)
+            {
+                if (displayLevel >= 1)
+                {
+        ;
+                }
+
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_parameter_outOfBound)));
+            }
+
+            if (accel == 0 || accel > 10)
+            {
+                if (displayLevel >= 1)
+                {
+        ;
+                }
+
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_parameter_outOfBound)));
+            }
+
+            if (kMinK < kMaxD || kMaxK < kMinK)
+            {
+                if (displayLevel >= 1)
+                {
+        ;
+                }
+
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_parameter_outOfBound)));
+            }
+
+            if (nbSamples == 0)
+            {
+                if (displayLevel >= 1)
+                {
+        ;
+                }
+
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_srcSize_wrong)));
+            }
+
+            if (dictBufferCapacity < 256)
+            {
+                if (displayLevel >= 1)
+                {
+        ;
+                }
+
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall)));
+            }
+
+            if (nbThreads > 1)
+            {
+                throw new NotImplementedException("Multiple threads are not supported");
+            }
+
+            COVER_best_init(&best);
+            memset((void*)&coverParams, 0, (nuint)(sizeof(ZDICT_cover_params_t)));
+            FASTCOVER_convertToCoverParams(*parameters, &coverParams);
+            accelParams = FASTCOVER_defaultAccelParameters[accel];
+            g_displayLevel = displayLevel == 0 ? 0 : displayLevel - 1;
+            if (displayLevel >= 2)
+            {
+        ;
+            }
+
+            for (d = kMinD; d <= kMaxD; d += 2)
+            {
+                FASTCOVER_ctx_t ctx;
+
+                if (displayLevel >= 3)
+                {
+        ;
+                }
+
+
+                {
+                    nuint initVal = FASTCOVER_ctx_init(&ctx, samplesBuffer, samplesSizes, nbSamples, d, splitPoint, f, accelParams);
+
+                    if ((ERR_isError(initVal)) != 0)
+                    {
+                        if (displayLevel >= 1)
+                        {
+        ;
+                        }
+
+                        COVER_best_destroy(&best);
+                        return initVal;
+                    }
+                }
+
+                if (warned == 0)
+                {
+                    COVER_warnOnSmallCorpus(dictBufferCapacity, ctx.nbDmers, displayLevel);
+                    warned = 1;
+                }
+
+                for (k = kMinK; k <= kMaxK; k += kStepSize)
+                {
+                    FASTCOVER_tryParameters_data_s* data = (FASTCOVER_tryParameters_data_s*)(malloc((nuint)(sizeof(FASTCOVER_tryParameters_data_s))));
+
+                    if (displayLevel >= 3)
+                    {
+        ;
+                    }
+
+                    if (data == null)
+                    {
+                        if (displayLevel >= 1)
+                        {
+        ;
+                        }
+
+                        COVER_best_destroy(&best);
+                        FASTCOVER_ctx_destroy(&ctx);
+                        return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_memory_allocation)));
+                    }
+
+                    data->ctx = &ctx;
+                    data->best = &best;
+                    data->dictBufferCapacity = dictBufferCapacity;
+                    data->parameters = coverParams;
+                    data->parameters.k = k;
+                    data->parameters.d = d;
+                    data->parameters.splitPoint = splitPoint;
+                    data->parameters.steps = kSteps;
+                    data->parameters.shrinkDict = shrinkDict;
+                    data->parameters.zParams.notificationLevel = (uint)g_displayLevel;
+                    if ((FASTCOVER_checkParameters(data->parameters, dictBufferCapacity, data->ctx->f, accel)) == 0)
+                    {
+                        free((void*)data);
+                        continue;
+                    }
+
+                    COVER_best_start(&best);
+                    FASTCOVER_tryParameters((void*)data);
+
+                    ++iteration;
+                }
+
+                COVER_best_wait(&best);
+                FASTCOVER_ctx_destroy(&ctx);
+            }
+
+            if (displayLevel >= 2)
+            {
+        ;
+            }
+
+
+            {
+                nuint dictSize = best.dictSize;
+
+                if ((ERR_isError(best.compressedSize)) != 0)
+                {
+                    nuint compressedSize = best.compressedSize;
+
+                    COVER_best_destroy(&best);
+                    return compressedSize;
+                }
+
+                FASTCOVER_convertToFastCoverParams(best.parameters, parameters, f, accel);
+                memcpy(dictBuffer, best.dict, dictSize);
+                COVER_best_destroy(&best);
+                return dictSize;
+            }
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/Fse.cs

@@ -0,0 +1,158 @@
+using System;
+using System.Runtime.CompilerServices;
+using static ZstdSharp.UnsafeHelper;
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void FSE_initCState(FSE_CState_t* statePtr, uint* ct)
+        {
+            void* ptr = (void*)ct;
+            ushort* u16ptr = (ushort*)(ptr);
+            uint tableLog = MEM_read16(ptr);
+
+            statePtr->value = (nint)(1) << (int)tableLog;
+            statePtr->stateTable = u16ptr + 2;
+            statePtr->symbolTT = ct + 1 + (tableLog != 0 ? (1 << (int)(tableLog - 1)) : 1);
+            statePtr->stateLog = tableLog;
+        }
+
+        /*! FSE_initCState2() :
+        *   Same as FSE_initCState(), but the first symbol to include (which will be the last to be read)
+        *   uses the smallest state value possible, saving the cost of this symbol */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void FSE_initCState2(FSE_CState_t* statePtr, uint* ct, uint symbol)
+        {
+            FSE_initCState(statePtr, ct);
+
+            {
+                FSE_symbolCompressionTransform symbolTT = ((FSE_symbolCompressionTransform*)(statePtr->symbolTT))[symbol];
+                ushort* stateTable = (ushort*)(statePtr->stateTable);
+                uint nbBitsOut = (uint)((symbolTT.deltaNbBits + (uint)((1 << 15))) >> 16);
+
+                statePtr->value = (nint)((nbBitsOut << 16) - symbolTT.deltaNbBits);
+                statePtr->value = (nint)(stateTable[(statePtr->value >> (int)nbBitsOut) + symbolTT.deltaFindState]);
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void FSE_encodeSymbol(BIT_CStream_t* bitC, FSE_CState_t* statePtr, uint symbol)
+        {
+            FSE_symbolCompressionTransform symbolTT = ((FSE_symbolCompressionTransform*)(statePtr->symbolTT))[symbol];
+            ushort* stateTable = (ushort*)(statePtr->stateTable);
+            uint nbBitsOut = (uint)(((nuint)statePtr->value + symbolTT.deltaNbBits) >> 16);
+
+            BIT_addBits(bitC, (nuint)statePtr->value, nbBitsOut);
+            statePtr->value = (nint)(stateTable[(statePtr->value >> (int)nbBitsOut) + symbolTT.deltaFindState]);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void FSE_flushCState(BIT_CStream_t* bitC, FSE_CState_t* statePtr)
+        {
+            BIT_addBits(bitC, (nuint)statePtr->value, statePtr->stateLog);
+            BIT_flushBits(bitC);
+        }
+
+        /* FSE_getMaxNbBits() :
+         * Approximate maximum cost of a symbol, in bits.
+         * Fractional get rounded up (i.e : a symbol with a normalized frequency of 3 gives the same result as a frequency of 2)
+         * note 1 : assume symbolValue is valid (<= maxSymbolValue)
+         * note 2 : if freq[symbolValue]==0, @return a fake cost of tableLog+1 bits */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static uint FSE_getMaxNbBits(void* symbolTTPtr, uint symbolValue)
+        {
+            FSE_symbolCompressionTransform* symbolTT = (FSE_symbolCompressionTransform*)(symbolTTPtr);
+
+            return (symbolTT[symbolValue].deltaNbBits + (uint)(((1 << 16) - 1))) >> 16;
+        }
+
+        /* FSE_bitCost() :
+         * Approximate symbol cost, as fractional value, using fixed-point format (accuracyLog fractional bits)
+         * note 1 : assume symbolValue is valid (<= maxSymbolValue)
+         * note 2 : if freq[symbolValue]==0, @return a fake cost of tableLog+1 bits */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static uint FSE_bitCost(void* symbolTTPtr, uint tableLog, uint symbolValue, uint accuracyLog)
+        {
+            FSE_symbolCompressionTransform* symbolTT = (FSE_symbolCompressionTransform*)(symbolTTPtr);
+            uint minNbBits = symbolTT[symbolValue].deltaNbBits >> 16;
+            uint threshold = (minNbBits + 1) << 16;
+
+            assert(tableLog < 16);
+            assert(accuracyLog < 31 - tableLog);
+
+            {
+                uint tableSize = (uint)(1 << (int)tableLog);
+                uint deltaFromThreshold = threshold - (symbolTT[symbolValue].deltaNbBits + tableSize);
+                uint normalizedDeltaFromThreshold = (deltaFromThreshold << (int)accuracyLog) >> (int)tableLog;
+                uint bitMultiplier = (uint)(1 << (int)accuracyLog);
+
+                assert(symbolTT[symbolValue].deltaNbBits + tableSize <= threshold);
+                assert(normalizedDeltaFromThreshold <= bitMultiplier);
+                return (minNbBits + 1) * bitMultiplier - normalizedDeltaFromThreshold;
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void FSE_initDState(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD, uint* dt)
+        {
+            void* ptr = (void*)dt;
+            FSE_DTableHeader* DTableH = (FSE_DTableHeader*)(ptr);
+
+            DStatePtr->state = BIT_readBits(bitD, DTableH->tableLog);
+            BIT_reloadDStream(bitD);
+            DStatePtr->table = dt + 1;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static byte FSE_peekSymbol(FSE_DState_t* DStatePtr)
+        {
+            FSE_decode_t DInfo = ((FSE_decode_t*)(DStatePtr->table))[DStatePtr->state];
+
+            return DInfo.symbol;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void FSE_updateState(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD)
+        {
+            FSE_decode_t DInfo = ((FSE_decode_t*)(DStatePtr->table))[DStatePtr->state];
+            uint nbBits = DInfo.nbBits;
+            nuint lowBits = BIT_readBits(bitD, nbBits);
+
+            DStatePtr->state = DInfo.newState + lowBits;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static byte FSE_decodeSymbol(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD)
+        {
+            FSE_decode_t DInfo = ((FSE_decode_t*)(DStatePtr->table))[DStatePtr->state];
+            uint nbBits = DInfo.nbBits;
+            byte symbol = DInfo.symbol;
+            nuint lowBits = BIT_readBits(bitD, nbBits);
+
+            DStatePtr->state = DInfo.newState + lowBits;
+            return symbol;
+        }
+
+        /*! FSE_decodeSymbolFast() :
+            unsafe, only works if no symbol has a probability > 50% */
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static byte FSE_decodeSymbolFast(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD)
+        {
+            FSE_decode_t DInfo = ((FSE_decode_t*)(DStatePtr->table))[DStatePtr->state];
+            uint nbBits = DInfo.nbBits;
+            byte symbol = DInfo.symbol;
+            nuint lowBits = BIT_readBitsFast(bitD, nbBits);
+
+            DStatePtr->state = DInfo.newState + lowBits;
+            return symbol;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static uint FSE_endOfDState(FSE_DState_t* DStatePtr)
+        {
+            return ((DStatePtr->state == 0) ? 1U : 0U);
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FseCompress.cs

@@ -0,0 +1,960 @@
+using System;
+using static ZstdSharp.UnsafeHelper;
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        /* FSE_buildCTable_wksp() :
+         * Same as FSE_buildCTable(), but using an externally allocated scratch buffer (`workSpace`).
+         * wkspSize should be sized to handle worst case situation, which is `1<<max_tableLog * sizeof(FSE_FUNCTION_TYPE)`
+         * workSpace must also be properly aligned with FSE_FUNCTION_TYPE requirements
+         */
+        public static nuint FSE_buildCTable_wksp(uint* ct, short* normalizedCounter, uint maxSymbolValue, uint tableLog, void* workSpace, nuint wkspSize)
+        {
+            uint tableSize = (uint)(1 << (int)tableLog);
+            uint tableMask = tableSize - 1;
+            void* ptr = (void*)ct;
+            ushort* tableU16 = ((ushort*)(ptr)) + 2;
+            void* FSCT = (void*)(((uint*)(ptr)) + 1 + (tableLog != 0 ? tableSize >> 1 : 1));
+            FSE_symbolCompressionTransform* symbolTT = (FSE_symbolCompressionTransform*)(FSCT);
+            uint step = (((tableSize) >> 1) + ((tableSize) >> 3) + 3);
+            uint* cumul = (uint*)(workSpace);
+            byte* tableSymbol = (byte*)(cumul + (maxSymbolValue + 2));
+            uint highThreshold = tableSize - 1;
+
+            if (((nuint)(workSpace) & 3) != 0)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            }
+
+            if (((nuint)(sizeof(uint)) * (maxSymbolValue + 2 + (1UL << (int)(tableLog - 2)))) > wkspSize)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_tableLog_tooLarge)));
+            }
+
+            tableU16[-2] = (ushort)(tableLog);
+            tableU16[-1] = (ushort)(maxSymbolValue);
+            assert(tableLog < 16);
+
+            {
+                uint u;
+
+                cumul[0] = 0;
+                for (u = 1; u <= maxSymbolValue + 1; u++)
+                {
+                    if (normalizedCounter[u - 1] == -1)
+                    {
+                        cumul[u] = cumul[u - 1] + 1;
+                        tableSymbol[highThreshold--] = (byte)(u - 1);
+                    }
+                    else
+                    {
+                        cumul[u] = cumul[u - 1] + (ushort)(normalizedCounter[u - 1]);
+                    }
+                }
+
+                cumul[maxSymbolValue + 1] = tableSize + 1;
+            }
+
+
+            {
+                uint position = 0;
+                uint symbol;
+
+                for (symbol = 0; symbol <= maxSymbolValue; symbol++)
+                {
+                    int nbOccurrences;
+                    int freq = normalizedCounter[symbol];
+
+                    for (nbOccurrences = 0; nbOccurrences < freq; nbOccurrences++)
+                    {
+                        tableSymbol[position] = (byte)(symbol);
+                        position = (position + step) & tableMask;
+                        while (position > highThreshold)
+                        {
+                            position = (position + step) & tableMask;
+                        }
+                    }
+                }
+
+                assert(position == 0);
+            }
+
+
+            {
+                uint u;
+
+                for (u = 0; u < tableSize; u++)
+                {
+                    byte s = tableSymbol[u];
+
+                    tableU16[cumul[s]++] = (ushort)(tableSize + u);
+                }
+            }
+
+
+            {
+                uint total = 0;
+                uint s;
+
+                for (s = 0; s <= maxSymbolValue; s++)
+                {
+                    switch (normalizedCounter[s])
+                    {
+                        case 0:
+                        {
+                            symbolTT[s].deltaNbBits = ((tableLog + 1) << 16) - (uint)((1 << (int)tableLog));
+                        }
+
+                        break;
+                        case -1:
+                        case 1:
+                        {
+                            symbolTT[s].deltaNbBits = (tableLog << 16) - (uint)((1 << (int)tableLog));
+                        }
+
+                        symbolTT[s].deltaFindState = (int)(total - 1);
+                        total++;
+                        break;
+                        default:
+                        {
+                            uint maxBitsOut = tableLog - BIT_highbit32((uint)(normalizedCounter[s] - 1));
+                            uint minStatePlus = (uint)(normalizedCounter[s] << (int)maxBitsOut);
+
+                            symbolTT[s].deltaNbBits = (maxBitsOut << 16) - minStatePlus;
+                            symbolTT[s].deltaFindState = (int)(total - (ushort)(normalizedCounter[s]));
+                            total += (uint)(normalizedCounter[s]);
+                        }
+                        break;
+                    }
+                }
+            }
+
+            return 0;
+        }
+
+        /*! FSE_buildCTable():
+            Builds `ct`, which must be already allocated, using FSE_createCTable().
+            @return : 0, or an errorCode, which can be tested using FSE_isError() */
+        public static nuint FSE_buildCTable(uint* ct, short* normalizedCounter, uint maxSymbolValue, uint tableLog)
+        {
+            byte* tableSymbol = stackalloc byte[4096];
+
+            return FSE_buildCTable_wksp(ct, normalizedCounter, maxSymbolValue, tableLog, (void*)tableSymbol, (nuint)(sizeof(byte) * 4096));
+        }
+
+        /*-**************************************************************
+        *  FSE NCount encoding
+        ****************************************************************/
+        public static nuint FSE_NCountWriteBound(uint maxSymbolValue, uint tableLog)
+        {
+            nuint maxHeaderSize = (((maxSymbolValue + 1) * tableLog) >> 3) + 3;
+
+            return maxSymbolValue != 0 ? maxHeaderSize : 512;
+        }
+
+        private static nuint FSE_writeNCount_generic(void* header, nuint headerBufferSize, short* normalizedCounter, uint maxSymbolValue, uint tableLog, uint writeIsSafe)
+        {
+            byte* ostart = (byte*)(header);
+            byte* @out = ostart;
+            byte* oend = ostart + headerBufferSize;
+            int nbBits;
+            int tableSize = 1 << (int)tableLog;
+            int remaining;
+            int threshold;
+            uint bitStream = 0;
+            int bitCount = 0;
+            uint symbol = 0;
+            uint alphabetSize = maxSymbolValue + 1;
+            int previousIs0 = 0;
+
+            bitStream += (tableLog - 5) << bitCount;
+            bitCount += 4;
+            remaining = tableSize + 1;
+            threshold = tableSize;
+            nbBits = (int)(tableLog + 1);
+            while ((symbol < alphabetSize) && (remaining > 1))
+            {
+                if (previousIs0 != 0)
+                {
+                    uint start = symbol;
+
+                    while ((symbol < alphabetSize) && (normalizedCounter[symbol]) == 0)
+                    {
+                        symbol++;
+                    }
+
+                    if (symbol == alphabetSize)
+                    {
+                        break;
+                    }
+
+                    while (symbol >= start + 24)
+                    {
+                        start += 24;
+                        bitStream += 0xFFFFU << bitCount;
+                        if (writeIsSafe == 0 && (@out > oend - 2))
+                        {
+                            return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall)));
+                        }
+
+                        @out[0] = (byte)(bitStream);
+                        @out[1] = (byte)(bitStream >> 8);
+                        @out += 2;
+                        bitStream >>= 16;
+                    }
+
+                    while (symbol >= start + 3)
+                    {
+                        start += 3;
+                        bitStream += (uint)(3 << bitCount);
+                        bitCount += 2;
+                    }
+
+                    bitStream += (symbol - start) << bitCount;
+                    bitCount += 2;
+                    if (bitCount > 16)
+                    {
+                        if (writeIsSafe == 0 && (@out > oend - 2))
+                        {
+                            return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall)));
+                        }
+
+                        @out[0] = (byte)(bitStream);
+                        @out[1] = (byte)(bitStream >> 8);
+                        @out += 2;
+                        bitStream >>= 16;
+                        bitCount -= 16;
+                    }
+                }
+
+
+                {
+                    int count = normalizedCounter[symbol++];
+                    int max = (2 * threshold - 1) - remaining;
+
+                    remaining -= count < 0 ? -count : count;
+                    count++;
+                    if (count >= threshold)
+                    {
+                        count += max;
+                    }
+
+                    bitStream += (uint)(count << bitCount);
+                    bitCount += nbBits;
+                    bitCount -= ((count < max) ? 1 : 0);
+                    previousIs0 = ((count == 1) ? 1 : 0);
+                    if (remaining < 1)
+                    {
+                        return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+                    }
+
+                    while (remaining < threshold)
+                    {
+                        nbBits--;
+                        threshold >>= 1;
+                    }
+                }
+
+                if (bitCount > 16)
+                {
+                    if (writeIsSafe == 0 && (@out > oend - 2))
+                    {
+                        return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall)));
+                    }
+
+                    @out[0] = (byte)(bitStream);
+                    @out[1] = (byte)(bitStream >> 8);
+                    @out += 2;
+                    bitStream >>= 16;
+                    bitCount -= 16;
+                }
+            }
+
+            if (remaining != 1)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            }
+
+            assert(symbol <= alphabetSize);
+            if (writeIsSafe == 0 && (@out > oend - 2))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall)));
+            }
+
+            @out[0] = (byte)(bitStream);
+            @out[1] = (byte)(bitStream >> 8);
+            @out += (bitCount + 7) / 8;
+            return (nuint)((@out - ostart));
+        }
+
+        /*! FSE_writeNCount():
+            Compactly save 'normalizedCounter' into 'buffer'.
+            @return : size of the compressed table,
+                      or an errorCode, which can be tested using FSE_isError(). */
+        public static nuint FSE_writeNCount(void* buffer, nuint bufferSize, short* normalizedCounter, uint maxSymbolValue, uint tableLog)
+        {
+            if (tableLog > (uint)((14 - 2)))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_tableLog_tooLarge)));
+            }
+
+            if (tableLog < 5)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            }
+
+            if (bufferSize < FSE_NCountWriteBound(maxSymbolValue, tableLog))
+            {
+                return FSE_writeNCount_generic(buffer, bufferSize, normalizedCounter, maxSymbolValue, tableLog, 0);
+            }
+
+            return FSE_writeNCount_generic(buffer, bufferSize, normalizedCounter, maxSymbolValue, tableLog, 1);
+        }
+
+        /*-**************************************************************
+        *  FSE Compression Code
+        ****************************************************************/
+        public static uint* FSE_createCTable(uint maxSymbolValue, uint tableLog)
+        {
+            nuint size;
+
+            if (tableLog > 15)
+            {
+                tableLog = 15;
+            }
+
+            size = ((uint)(1 + (1 << (int)((tableLog) - 1))) + (((maxSymbolValue) + 1) * 2)) * (nuint)(sizeof(uint));
+            return (uint*)(malloc(size));
+        }
+
+        public static void FSE_freeCTable(uint* ct)
+        {
+            free((void*)(ct));
+        }
+
+        /* provides the minimum logSize to safely represent a distribution */
+        [InlineMethod.Inline]
+        private static uint FSE_minTableLog(nuint srcSize, uint maxSymbolValue)
+        {
+            uint minBitsSrc = BIT_highbit32((uint)(srcSize)) + 1;
+            uint minBitsSymbols = BIT_highbit32(maxSymbolValue) + 2;
+            uint minBits = minBitsSrc < minBitsSymbols ? minBitsSrc : minBitsSymbols;
+
+            assert(srcSize > 1);
+            return minBits;
+        }
+
+        /* *****************************************
+         *  FSE advanced API
+         ***************************************** */
+        public static uint FSE_optimalTableLog_internal(uint maxTableLog, nuint srcSize, uint maxSymbolValue, uint minus)
+        {
+            uint maxBitsSrc = BIT_highbit32((uint)(srcSize - 1)) - minus;
+            uint tableLog = maxTableLog;
+            uint minBits = FSE_minTableLog(srcSize, maxSymbolValue);
+
+            assert(srcSize > 1);
+            if (tableLog == 0)
+            {
+                tableLog = (uint)((13 - 2));
+            }
+
+            if (maxBitsSrc < tableLog)
+            {
+                tableLog = maxBitsSrc;
+            }
+
+            if (minBits > tableLog)
+            {
+                tableLog = minBits;
+            }
+
+            if (tableLog < 5)
+            {
+                tableLog = 5;
+            }
+
+            if (tableLog > (uint)((14 - 2)))
+            {
+                tableLog = (uint)((14 - 2));
+            }
+
+            return tableLog;
+        }
+
+        /*! FSE_optimalTableLog():
+            dynamically downsize 'tableLog' when conditions are met.
+            It saves CPU time, by using smaller tables, while preserving or even improving compression ratio.
+            @return : recommended tableLog (necessarily <= 'maxTableLog') */
+        public static uint FSE_optimalTableLog(uint maxTableLog, nuint srcSize, uint maxSymbolValue)
+        {
+            return FSE_optimalTableLog_internal(maxTableLog, srcSize, maxSymbolValue, 2);
+        }
+
+        /* Secondary normalization method.
+           To be used when primary method fails. */
+        private static nuint FSE_normalizeM2(short* norm, uint tableLog, uint* count, nuint total, uint maxSymbolValue, short lowProbCount)
+        {
+            short NOT_YET_ASSIGNED = (short)-2;
+            uint s;
+            uint distributed = 0;
+            uint ToDistribute;
+            uint lowThreshold = (uint)(total >> (int)tableLog);
+            uint lowOne = (uint)((total * 3) >> (int)(tableLog + 1));
+
+            for (s = 0; s <= maxSymbolValue; s++)
+            {
+                if (count[s] == 0)
+                {
+                    norm[s] = 0;
+                    continue;
+                }
+
+                if (count[s] <= lowThreshold)
+                {
+                    norm[s] = lowProbCount;
+                    distributed++;
+                    total -= count[s];
+                    continue;
+                }
+
+                if (count[s] <= lowOne)
+                {
+                    norm[s] = 1;
+                    distributed++;
+                    total -= count[s];
+                    continue;
+                }
+
+                norm[s] = NOT_YET_ASSIGNED;
+            }
+
+            ToDistribute = (uint)((1 << (int)tableLog)) - distributed;
+            if (ToDistribute == 0)
+            {
+                return 0;
+            }
+
+            if ((total / ToDistribute) > lowOne)
+            {
+                lowOne = (uint)((total * 3) / (ToDistribute * 2));
+                for (s = 0; s <= maxSymbolValue; s++)
+                {
+                    if ((norm[s] == NOT_YET_ASSIGNED) && (count[s] <= lowOne))
+                    {
+                        norm[s] = 1;
+                        distributed++;
+                        total -= count[s];
+                        continue;
+                    }
+                }
+
+                ToDistribute = (uint)((1 << (int)tableLog)) - distributed;
+            }
+
+            if (distributed == maxSymbolValue + 1)
+            {
+                uint maxV = 0, maxC = 0;
+
+                for (s = 0; s <= maxSymbolValue; s++)
+                {
+                    if (count[s] > maxC)
+                    {
+                        maxV = s;
+                        maxC = count[s];
+                    }
+                }
+
+                norm[maxV] += (short)(short)(ToDistribute);
+                return 0;
+            }
+
+            if (total == 0)
+            {
+                for (s = 0; ToDistribute > 0; s = (s + 1) % (maxSymbolValue + 1))
+                {
+                    if (norm[s] > 0)
+                    {
+                        ToDistribute--;
+                        norm[s]++;
+                    }
+                }
+
+                return 0;
+            }
+
+
+            {
+                ulong vStepLog = 62 - tableLog;
+                ulong mid = (1UL << (int)(vStepLog - 1)) - 1;
+                ulong rStep = (((((ulong)(1) << (int)vStepLog) * ToDistribute) + mid) / ((uint)(total)));
+                ulong tmpTotal = mid;
+
+                for (s = 0; s <= maxSymbolValue; s++)
+                {
+                    if (norm[s] == NOT_YET_ASSIGNED)
+                    {
+                        ulong end = tmpTotal + (count[s] * rStep);
+                        uint sStart = (uint)(tmpTotal >> (int)vStepLog);
+                        uint sEnd = (uint)(end >> (int)vStepLog);
+                        uint weight = sEnd - sStart;
+
+                        if (weight < 1)
+                        {
+                            return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+                        }
+
+                        norm[s] = (short)(weight);
+                        tmpTotal = end;
+                    }
+                }
+            }
+
+            return 0;
+        }
+
+        /*! FSE_normalizeCount():
+            normalize counts so that sum(count[]) == Power_of_2 (2^tableLog)
+            'normalizedCounter' is a table of short, of minimum size (maxSymbolValue+1).
+            useLowProbCount is a boolean parameter which trades off compressed size for
+            faster header decoding. When it is set to 1, the compressed data will be slightly
+            smaller. And when it is set to 0, FSE_readNCount() and FSE_buildDTable() will be
+            faster. If you are compressing a small amount of data (< 2 KB) then useLowProbCount=0
+            is a good default, since header deserialization makes a big speed difference.
+            Otherwise, useLowProbCount=1 is a good default, since the speed difference is small.
+            @return : tableLog,
+                      or an errorCode, which can be tested using FSE_isError() */
+        public static nuint FSE_normalizeCount(short* normalizedCounter, uint tableLog, uint* count, nuint total, uint maxSymbolValue, uint useLowProbCount)
+        {
+            if (tableLog == 0)
+            {
+                tableLog = (uint)((13 - 2));
+            }
+
+            if (tableLog < 5)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            }
+
+            if (tableLog > (uint)((14 - 2)))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_tableLog_tooLarge)));
+            }
+
+            if (tableLog < FSE_minTableLog(total, maxSymbolValue))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            }
+
+
+            {
+
+                short lowProbCount = (short)(useLowProbCount != 0 ? -1 : 1);
+                ulong scale = 62 - tableLog;
+                ulong step = (((ulong)(1) << 62) / ((uint)(total)));
+                ulong vStep = 1UL << (int)(scale - 20);
+                int stillToDistribute = 1 << (int)tableLog;
+                uint s;
+                uint largest = 0;
+                short largestP = 0;
+                uint lowThreshold = (uint)(total >> (int)tableLog);
+
+                for (s = 0; s <= maxSymbolValue; s++)
+                {
+                    if (count[s] == total)
+                    {
+                        return 0;
+                    }
+
+                    if (count[s] == 0)
+                    {
+                        normalizedCounter[s] = 0;
+                        continue;
+                    }
+
+                    if (count[s] <= lowThreshold)
+                    {
+                        normalizedCounter[s] = lowProbCount;
+                        stillToDistribute--;
+                    }
+                    else
+                    {
+                        short proba = (short)((count[s] * step) >> (int)scale);
+
+                        if (proba < 8)
+                        {
+                            ulong restToBeat = vStep * rtbTable[proba];
+
+                            proba += (short)((((count[s] * step) - ((ulong)(proba) << (int)scale) > restToBeat) ? 1 : 0));
+                        }
+
+                        if (proba > largestP)
+                        {
+                            largestP = proba;
+                            largest = s;
+                        }
+
+                        normalizedCounter[s] = proba;
+                        stillToDistribute -= proba;
+                    }
+                }
+
+                if (-stillToDistribute >= (normalizedCounter[largest] >> 1))
+                {
+                    nuint errorCode = FSE_normalizeM2(normalizedCounter, tableLog, count, total, maxSymbolValue, lowProbCount);
+
+                    if ((ERR_isError(errorCode)) != 0)
+                    {
+                        return errorCode;
+                    }
+                }
+                else
+                {
+                    normalizedCounter[largest] += (short)(short)(stillToDistribute);
+                }
+            }
+
+            return tableLog;
+        }
+
+        /* fake FSE_CTable, for raw (uncompressed) input */
+        public static nuint FSE_buildCTable_raw(uint* ct, uint nbBits)
+        {
+            uint tableSize = (uint)(1 << (int)nbBits);
+            uint tableMask = tableSize - 1;
+            uint maxSymbolValue = tableMask;
+            void* ptr = (void*)ct;
+            ushort* tableU16 = ((ushort*)(ptr)) + 2;
+            void* FSCT = (void*)(((uint*)(ptr)) + 1 + (tableSize >> 1));
+            FSE_symbolCompressionTransform* symbolTT = (FSE_symbolCompressionTransform*)(FSCT);
+            uint s;
+
+            if (nbBits < 1)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            }
+
+            tableU16[-2] = (ushort)(nbBits);
+            tableU16[-1] = (ushort)(maxSymbolValue);
+            for (s = 0; s < tableSize; s++)
+            {
+                tableU16[s] = (ushort)(tableSize + s);
+            }
+
+
+            {
+                uint deltaNbBits = (nbBits << 16) - (uint)((1 << (int)nbBits));
+
+                for (s = 0; s <= maxSymbolValue; s++)
+                {
+                    symbolTT[s].deltaNbBits = deltaNbBits;
+                    symbolTT[s].deltaFindState = (int)(s - 1);
+                }
+            }
+
+            return 0;
+        }
+
+        /* fake FSE_CTable, for rle input (always same symbol) */
+        public static nuint FSE_buildCTable_rle(uint* ct, byte symbolValue)
+        {
+            void* ptr = (void*)ct;
+            ushort* tableU16 = ((ushort*)(ptr)) + 2;
+            void* FSCTptr = (void*)((uint*)(ptr) + 2);
+            FSE_symbolCompressionTransform* symbolTT = (FSE_symbolCompressionTransform*)(FSCTptr);
+
+            tableU16[-2] = (ushort)(0);
+            tableU16[-1] = (ushort)(symbolValue);
+            tableU16[0] = 0;
+            tableU16[1] = 0;
+            symbolTT[symbolValue].deltaNbBits = 0;
+            symbolTT[symbolValue].deltaFindState = 0;
+            return 0;
+        }
+
+        private static nuint FSE_compress_usingCTable_generic(void* dst, nuint dstSize, void* src, nuint srcSize, uint* ct, uint fast)
+        {
+            byte* istart = (byte*)(src);
+            byte* iend = istart + srcSize;
+            byte* ip = iend;
+            BIT_CStream_t bitC;
+            FSE_CState_t CState1, CState2;
+
+            if (srcSize <= 2)
+            {
+                return 0;
+            }
+
+
+            {
+                nuint initError = BIT_initCStream(&bitC, dst, dstSize);
+
+                if ((ERR_isError(initError)) != 0)
+                {
+                    return 0;
+                }
+            }
+
+            if ((srcSize & 1) != 0)
+            {
+                FSE_initCState2(&CState1, ct, *--ip);
+                FSE_initCState2(&CState2, ct, *--ip);
+                FSE_encodeSymbol(&bitC, &CState1, *--ip);
+                if (fast != 0)
+                {
+                    BIT_flushBitsFast(&bitC);
+                }
+                else
+                {
+                    BIT_flushBits(&bitC);
+                }
+
+            }
+            else
+            {
+                FSE_initCState2(&CState2, ct, *--ip);
+                FSE_initCState2(&CState1, ct, *--ip);
+            }
+
+            srcSize -= 2;
+            if (((nuint)(sizeof(nuint)) * 8 > (uint)((14 - 2) * 4 + 7)) && (srcSize & 2) != 0)
+            {
+                FSE_encodeSymbol(&bitC, &CState2, *--ip);
+                FSE_encodeSymbol(&bitC, &CState1, *--ip);
+                if (fast != 0)
+                {
+                    BIT_flushBitsFast(&bitC);
+                }
+                else
+                {
+                    BIT_flushBits(&bitC);
+                }
+
+            }
+
+            while (ip > istart)
+            {
+                FSE_encodeSymbol(&bitC, &CState2, *--ip);
+                if ((nuint)(sizeof(nuint)) * 8 < (uint)((14 - 2) * 2 + 7))
+                {
+                    if (fast != 0)
+                    {
+                        BIT_flushBitsFast(&bitC);
+                    }
+                    else
+                    {
+                        BIT_flushBits(&bitC);
+                    }
+                }
+
+                FSE_encodeSymbol(&bitC, &CState1, *--ip);
+                if ((nuint)(sizeof(nuint)) * 8 > (uint)((14 - 2) * 4 + 7))
+                {
+                    FSE_encodeSymbol(&bitC, &CState2, *--ip);
+                    FSE_encodeSymbol(&bitC, &CState1, *--ip);
+                }
+
+                if (fast != 0)
+                {
+                    BIT_flushBitsFast(&bitC);
+                }
+                else
+                {
+                    BIT_flushBits(&bitC);
+                }
+
+            }
+
+            FSE_flushCState(&bitC, &CState2);
+            FSE_flushCState(&bitC, &CState1);
+            return BIT_closeCStream(&bitC);
+        }
+
+        /*! FSE_compress_usingCTable():
+            Compress `src` using `ct` into `dst` which must be already allocated.
+            @return : size of compressed data (<= `dstCapacity`),
+                      or 0 if compressed data could not fit into `dst`,
+                      or an errorCode, which can be tested using FSE_isError() */
+        public static nuint FSE_compress_usingCTable(void* dst, nuint dstSize, void* src, nuint srcSize, uint* ct)
+        {
+            uint fast = (((dstSize >= ((srcSize) + ((srcSize) >> 7) + 4 + (nuint)(sizeof(nuint))))) ? 1U : 0U);
+
+            if (fast != 0)
+            {
+                return FSE_compress_usingCTable_generic(dst, dstSize, src, srcSize, ct, 1);
+            }
+            else
+            {
+                return FSE_compress_usingCTable_generic(dst, dstSize, src, srcSize, ct, 0);
+            }
+        }
+
+        /*-*****************************************
+        *  Tool functions
+        ******************************************/
+        public static nuint FSE_compressBound(nuint size)
+        {
+            return (512 + ((size) + ((size) >> 7) + 4 + (nuint)(sizeof(nuint))));
+        }
+
+        /* FSE_compress_wksp() :
+         * Same as FSE_compress2(), but using an externally allocated scratch buffer (`workSpace`).
+         * `wkspSize` size must be `(1<<tableLog)`.
+         */
+        public static nuint FSE_compress_wksp(void* dst, nuint dstSize, void* src, nuint srcSize, uint maxSymbolValue, uint tableLog, void* workSpace, nuint wkspSize)
+        {
+            byte* ostart = (byte*)(dst);
+            byte* op = ostart;
+            byte* oend = ostart + dstSize;
+            uint* count = stackalloc uint[256];
+            short* norm = stackalloc short[256];
+            uint* CTable = (uint*)(workSpace);
+            nuint CTableSize = ((uint)(1 + (1 << (int)((tableLog) - 1))) + (((maxSymbolValue) + 1) * 2));
+            void* scratchBuffer = (void*)(CTable + CTableSize);
+            nuint scratchBufferSize = wkspSize - (CTableSize * (nuint)(4));
+
+            if (wkspSize < (((uint)(1 + (1 << (int)((tableLog) - 1))) + (((maxSymbolValue) + 1) * 2)) + (uint)(((tableLog > 12) ? (1 << (int)(tableLog - 2)) : 1024))))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_tableLog_tooLarge)));
+            }
+
+            if (srcSize <= 1)
+            {
+                return 0;
+            }
+
+            if (maxSymbolValue == 0)
+            {
+                maxSymbolValue = 255;
+            }
+
+            if (tableLog == 0)
+            {
+                tableLog = (uint)((13 - 2));
+            }
+
+
+            {
+                nuint maxCount = HIST_count_wksp((uint*)count, &maxSymbolValue, src, srcSize, scratchBuffer, scratchBufferSize);
+
+                if ((ERR_isError(maxCount)) != 0)
+                {
+                    return maxCount;
+                }
+
+                if (maxCount == srcSize)
+                {
+                    return 1;
+                }
+
+                if (maxCount == 1)
+                {
+                    return 0;
+                }
+
+                if (maxCount < (srcSize >> 7))
+                {
+                    return 0;
+                }
+            }
+
+            tableLog = FSE_optimalTableLog(tableLog, srcSize, maxSymbolValue);
+
+            {
+                nuint _var_err__ = FSE_normalizeCount((short*)norm, tableLog, (uint*)count, srcSize, maxSymbolValue, ((srcSize >= 2048) ? 1U : 0U));
+
+                if ((ERR_isError(_var_err__)) != 0)
+                {
+                    return _var_err__;
+                }
+            }
+
+
+            {
+                nuint nc_err = FSE_writeNCount((void*)op, (nuint)(oend - op), (short*)norm, maxSymbolValue, tableLog);
+
+                if ((ERR_isError(nc_err)) != 0)
+                {
+                    return nc_err;
+                }
+
+                op += nc_err;
+            }
+
+
+            {
+                nuint _var_err__ = FSE_buildCTable_wksp(CTable, (short*)norm, maxSymbolValue, tableLog, scratchBuffer, scratchBufferSize);
+
+                if ((ERR_isError(_var_err__)) != 0)
+                {
+                    return _var_err__;
+                }
+            }
+
+
+            {
+                nuint cSize = FSE_compress_usingCTable((void*)op, (nuint)(oend - op), src, srcSize, CTable);
+
+                if ((ERR_isError(cSize)) != 0)
+                {
+                    return cSize;
+                }
+
+                if (cSize == 0)
+                {
+                    return 0;
+                }
+
+                op += cSize;
+            }
+
+            if ((nuint)(op - ostart) >= srcSize - 1)
+            {
+                return 0;
+            }
+
+            return (nuint)(op - ostart);
+        }
+
+        /*-*****************************************
+        *  FSE advanced functions
+        ******************************************/
+        /*! FSE_compress2() :
+            Same as FSE_compress(), but allows the selection of 'maxSymbolValue' and 'tableLog'
+            Both parameters can be defined as '0' to mean : use default value
+            @return : size of compressed data
+            Special values : if return == 0, srcData is not compressible => Nothing is stored within cSrc !!!
+                             if return == 1, srcData is a single byte symbol * srcSize times. Use RLE compression.
+                             if FSE_isError(return), it's an error code.
+        */
+        public static nuint FSE_compress2(void* dst, nuint dstCapacity, void* src, nuint srcSize, uint maxSymbolValue, uint tableLog)
+        {
+            fseWkspMax_t scratchBuffer;
+
+            if (tableLog > (uint)((14 - 2)))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_tableLog_tooLarge)));
+            }
+
+            return FSE_compress_wksp(dst, dstCapacity, src, srcSize, maxSymbolValue, tableLog, (void*)&scratchBuffer, (nuint)(sizeof(fseWkspMax_t)));
+        }
+
+        /*-****************************************
+        *  FSE simple functions
+        ******************************************/
+        /*! FSE_compress() :
+            Compress content of buffer 'src', of size 'srcSize', into destination buffer 'dst'.
+            'dst' buffer must be already allocated. Compression runs faster is dstCapacity >= FSE_compressBound(srcSize).
+            @return : size of compressed data (<= dstCapacity).
+            Special values : if return == 0, srcData is not compressible => Nothing is stored within dst !!!
+                             if return == 1, srcData is a single byte symbol * srcSize times. Use RLE compression instead.
+                             if FSE_isError(return), compression failed (more details using FSE_getErrorName())
+        */
+        public static nuint FSE_compress(void* dst, nuint dstCapacity, void* src, nuint srcSize)
+        {
+            return FSE_compress2(dst, dstCapacity, src, srcSize, 255, (uint)((13 - 2)));
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/FseDecompress.cs

@@ -0,0 +1,446 @@
+using System;
+using System.Runtime.CompilerServices;
+using static ZstdSharp.UnsafeHelper;
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        /* Function templates */
+        public static uint* FSE_createDTable(uint tableLog)
+        {
+            if (tableLog > 15)
+            {
+                tableLog = 15;
+            }
+
+            return (uint*)(malloc((uint)((1 + (1 << (int)(tableLog)))) * (nuint)(sizeof(uint))));
+        }
+
+        public static void FSE_freeDTable(uint* dt)
+        {
+            free((void*)(dt));
+        }
+
+        private static nuint FSE_buildDTable_internal(uint* dt, short* normalizedCounter, uint maxSymbolValue, uint tableLog, void* workSpace, nuint wkspSize)
+        {
+            void* tdPtr = (void*)(dt + 1);
+            FSE_decode_t* tableDecode = (FSE_decode_t*)(tdPtr);
+            ushort* symbolNext = (ushort*)(workSpace);
+            byte* spread = (byte*)(symbolNext + maxSymbolValue + 1);
+            uint maxSV1 = maxSymbolValue + 1;
+            uint tableSize = (uint)(1 << (int)tableLog);
+            uint highThreshold = tableSize - 1;
+
+            if (((nuint)(sizeof(short)) * (maxSymbolValue + 1) + (1UL << (int)tableLog) + 8) > wkspSize)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_maxSymbolValue_tooLarge)));
+            }
+
+            if (maxSymbolValue > 255)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_maxSymbolValue_tooLarge)));
+            }
+
+            if (tableLog > (uint)((14 - 2)))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_tableLog_tooLarge)));
+            }
+
+
+            {
+                FSE_DTableHeader DTableH;
+
+                DTableH.tableLog = (ushort)(tableLog);
+                DTableH.fastMode = 1;
+
+                {
+                    short largeLimit = (short)(1 << (int)(tableLog - 1));
+                    uint s;
+
+                    for (s = 0; s < maxSV1; s++)
+                    {
+                        if (normalizedCounter[s] == -1)
+                        {
+                            tableDecode[highThreshold--].symbol = (byte)(s);
+                            symbolNext[s] = 1;
+                        }
+                        else
+                        {
+                            if (normalizedCounter[s] >= largeLimit)
+                            {
+                                DTableH.fastMode = 0;
+                            }
+
+                            symbolNext[s] = (ushort)(normalizedCounter[s]);
+                        }
+                    }
+                }
+
+                memcpy((void*)(dt), (void*)(&DTableH), ((nuint)(sizeof(FSE_DTableHeader))));
+            }
+
+            if (highThreshold == tableSize - 1)
+            {
+                nuint tableMask = tableSize - 1;
+                nuint step = (((tableSize) >> 1) + ((tableSize) >> 3) + 3);
+
+
+                {
+                    ulong add = 0x0101010101010101UL;
+                    nuint pos = 0;
+                    ulong sv = 0;
+                    uint s;
+
+                    for (s = 0; s < maxSV1; ++s , sv += add)
+                    {
+                        int i;
+                        int n = normalizedCounter[s];
+
+                        MEM_write64((void*)(spread + pos), sv);
+                        for (i = 8; i < n; i += 8)
+                        {
+                            MEM_write64((void*)(spread + pos + i), sv);
+                        }
+
+                        pos += (nuint)n;
+                    }
+                }
+
+
+                {
+                    nuint position = 0;
+                    nuint s;
+                    nuint unroll = 2;
+
+                    assert(tableSize % unroll == 0);
+                    for (s = 0; s < (nuint)(tableSize); s += unroll)
+                    {
+                        nuint u;
+
+                        for (u = 0; u < unroll; ++u)
+                        {
+                            nuint uPosition = (position + (u * step)) & tableMask;
+
+                            tableDecode[uPosition].symbol = spread[s + u];
+                        }
+
+                        position = (position + (unroll * step)) & tableMask;
+                    }
+
+                    assert(position == 0);
+                }
+            }
+            else
+            {
+                uint tableMask = tableSize - 1;
+                uint step = (((tableSize) >> 1) + ((tableSize) >> 3) + 3);
+                uint s, position = 0;
+
+                for (s = 0; s < maxSV1; s++)
+                {
+                    int i;
+
+                    for (i = 0; i < normalizedCounter[s]; i++)
+                    {
+                        tableDecode[position].symbol = (byte)(s);
+                        position = (position + step) & tableMask;
+                        while (position > highThreshold)
+                        {
+                            position = (position + step) & tableMask;
+                        }
+                    }
+                }
+
+                if (position != 0)
+                {
+                    return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+                }
+            }
+
+
+            {
+                uint u;
+
+                for (u = 0; u < tableSize; u++)
+                {
+                    byte symbol = (byte)(tableDecode[u].symbol);
+                    uint nextState = symbolNext[symbol]++;
+
+                    tableDecode[u].nbBits = (byte)(tableLog - BIT_highbit32(nextState));
+                    tableDecode[u].newState = (ushort)((nextState << (int)(tableDecode[u].nbBits)) - tableSize);
+                }
+            }
+
+            return 0;
+        }
+
+        public static nuint FSE_buildDTable_wksp(uint* dt, short* normalizedCounter, uint maxSymbolValue, uint tableLog, void* workSpace, nuint wkspSize)
+        {
+            return FSE_buildDTable_internal(dt, normalizedCounter, maxSymbolValue, tableLog, workSpace, wkspSize);
+        }
+
+        /*-*******************************************************
+        *  Decompression (Byte symbols)
+        *********************************************************/
+        public static nuint FSE_buildDTable_rle(uint* dt, byte symbolValue)
+        {
+            void* ptr = (void*)dt;
+            FSE_DTableHeader* DTableH = (FSE_DTableHeader*)(ptr);
+            void* dPtr = (void*)(dt + 1);
+            FSE_decode_t* cell = (FSE_decode_t*)(dPtr);
+
+            DTableH->tableLog = 0;
+            DTableH->fastMode = 0;
+            cell->newState = 0;
+            cell->symbol = symbolValue;
+            cell->nbBits = 0;
+            return 0;
+        }
+
+        public static nuint FSE_buildDTable_raw(uint* dt, uint nbBits)
+        {
+            void* ptr = (void*)dt;
+            FSE_DTableHeader* DTableH = (FSE_DTableHeader*)(ptr);
+            void* dPtr = (void*)(dt + 1);
+            FSE_decode_t* dinfo = (FSE_decode_t*)(dPtr);
+            uint tableSize = (uint)(1 << (int)nbBits);
+            uint tableMask = tableSize - 1;
+            uint maxSV1 = tableMask + 1;
+            uint s;
+
+            if (nbBits < 1)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            }
+
+            DTableH->tableLog = (ushort)(nbBits);
+            DTableH->fastMode = 1;
+            for (s = 0; s < maxSV1; s++)
+            {
+                dinfo[s].newState = 0;
+                dinfo[s].symbol = (byte)(s);
+                dinfo[s].nbBits = (byte)(nbBits);
+            }
+
+            return 0;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint FSE_decompress_usingDTable_generic(void* dst, nuint maxDstSize, void* cSrc, nuint cSrcSize, uint* dt, uint fast)
+        {
+            byte* ostart = (byte*)(dst);
+            byte* op = ostart;
+            byte* omax = op + maxDstSize;
+            byte* olimit = omax - 3;
+            BIT_DStream_t bitD;
+            FSE_DState_t state1;
+            FSE_DState_t state2;
+
+
+            {
+                nuint _var_err__ = BIT_initDStream(&bitD, cSrc, cSrcSize);
+
+                if ((ERR_isError(_var_err__)) != 0)
+                {
+                    return _var_err__;
+                }
+            }
+
+            FSE_initDState(&state1, &bitD, dt);
+            FSE_initDState(&state2, &bitD, dt);
+            for (; ((BIT_reloadDStream(&bitD) == BIT_DStream_status.BIT_DStream_unfinished) && (op < olimit)); op += 4)
+            {
+                op[0] = fast != 0 ? FSE_decodeSymbolFast(&state1, &bitD) : FSE_decodeSymbol(&state1, &bitD);
+                if ((uint)((14 - 2) * 2 + 7) > (nuint)(sizeof(nuint)) * 8)
+                {
+                    BIT_reloadDStream(&bitD);
+                }
+
+                op[1] = fast != 0 ? FSE_decodeSymbolFast(&state2, &bitD) : FSE_decodeSymbol(&state2, &bitD);
+                if ((uint)((14 - 2) * 4 + 7) > (nuint)(sizeof(nuint)) * 8)
+                {
+                    if (BIT_reloadDStream(&bitD) > BIT_DStream_status.BIT_DStream_unfinished)
+                    {
+                        op += 2;
+                        break;
+                    }
+                }
+
+                op[2] = fast != 0 ? FSE_decodeSymbolFast(&state1, &bitD) : FSE_decodeSymbol(&state1, &bitD);
+                if ((uint)((14 - 2) * 2 + 7) > (nuint)(sizeof(nuint)) * 8)
+                {
+                    BIT_reloadDStream(&bitD);
+                }
+
+                op[3] = fast != 0 ? FSE_decodeSymbolFast(&state2, &bitD) : FSE_decodeSymbol(&state2, &bitD);
+            }
+
+            while (1 != 0)
+            {
+                if (op > (omax - 2))
+                {
+                    return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall)));
+                }
+
+                *op++ = fast != 0 ? FSE_decodeSymbolFast(&state1, &bitD) : FSE_decodeSymbol(&state1, &bitD);
+                if (BIT_reloadDStream(&bitD) == BIT_DStream_status.BIT_DStream_overflow)
+                {
+                    *op++ = fast != 0 ? FSE_decodeSymbolFast(&state2, &bitD) : FSE_decodeSymbol(&state2, &bitD);
+                    break;
+                }
+
+                if (op > (omax - 2))
+                {
+                    return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_dstSize_tooSmall)));
+                }
+
+                *op++ = fast != 0 ? FSE_decodeSymbolFast(&state2, &bitD) : FSE_decodeSymbol(&state2, &bitD);
+                if (BIT_reloadDStream(&bitD) == BIT_DStream_status.BIT_DStream_overflow)
+                {
+                    *op++ = fast != 0 ? FSE_decodeSymbolFast(&state1, &bitD) : FSE_decodeSymbol(&state1, &bitD);
+                    break;
+                }
+            }
+
+            return (nuint)(op - ostart);
+        }
+
+        /*! FSE_decompress_usingDTable():
+            Decompress compressed source `cSrc` of size `cSrcSize` using `dt`
+            into `dst` which must be already allocated.
+            @return : size of regenerated data (necessarily <= `dstCapacity`),
+                      or an errorCode, which can be tested using FSE_isError() */
+        public static nuint FSE_decompress_usingDTable(void* dst, nuint originalSize, void* cSrc, nuint cSrcSize, uint* dt)
+        {
+            void* ptr = (void*)dt;
+            FSE_DTableHeader* DTableH = (FSE_DTableHeader*)(ptr);
+            uint fastMode = DTableH->fastMode;
+
+            if (fastMode != 0)
+            {
+                return FSE_decompress_usingDTable_generic(dst, originalSize, cSrc, cSrcSize, dt, 1);
+            }
+
+            return FSE_decompress_usingDTable_generic(dst, originalSize, cSrc, cSrcSize, dt, 0);
+        }
+
+        public static nuint FSE_decompress_wksp(void* dst, nuint dstCapacity, void* cSrc, nuint cSrcSize, uint maxLog, void* workSpace, nuint wkspSize)
+        {
+            return FSE_decompress_wksp_bmi2(dst, dstCapacity, cSrc, cSrcSize, maxLog, workSpace, wkspSize, 0);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static nuint FSE_decompress_wksp_body(void* dst, nuint dstCapacity, void* cSrc, nuint cSrcSize, uint maxLog, void* workSpace, nuint wkspSize, int bmi2)
+        {
+            byte* istart = (byte*)(cSrc);
+            byte* ip = istart;
+            uint tableLog;
+            uint maxSymbolValue = 255;
+            FSE_DecompressWksp* wksp = (FSE_DecompressWksp*)(workSpace);
+
+            if (wkspSize < (nuint)(sizeof(FSE_DecompressWksp)))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            }
+
+
+            {
+                nuint NCountLength = FSE_readNCount_bmi2((short*)wksp->ncount, &maxSymbolValue, &tableLog, (void*)istart, cSrcSize, bmi2);
+
+                if ((ERR_isError(NCountLength)) != 0)
+                {
+                    return NCountLength;
+                }
+
+                if (tableLog > maxLog)
+                {
+                    return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_tableLog_tooLarge)));
+                }
+
+                assert(NCountLength <= cSrcSize);
+                ip += NCountLength;
+                cSrcSize -= NCountLength;
+            }
+
+            if ((((uint)((1 + (1 << (int)(tableLog)))) + ((((nuint)(sizeof(short)) * (maxSymbolValue + 1) + (1UL << (int)tableLog) + 8) + (nuint)(sizeof(uint)) - 1) / (nuint)(sizeof(uint))) + (uint)((255 + 1) / 2) + 1) * (nuint)(sizeof(uint))) > wkspSize)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_tableLog_tooLarge)));
+            }
+
+            workSpace = wksp->dtable + (1 + (1 << (int)(tableLog)));
+            wkspSize -= (nuint)(sizeof(FSE_DecompressWksp)) + ((uint)((1 + (1 << (int)(tableLog)))) * (nuint)(sizeof(uint)));
+
+            {
+                nuint _var_err__ = FSE_buildDTable_internal((uint*)wksp->dtable, (short*)wksp->ncount, maxSymbolValue, tableLog, workSpace, wkspSize);
+
+                if ((ERR_isError(_var_err__)) != 0)
+                {
+                    return _var_err__;
+                }
+            }
+
+
+            {
+                void* ptr = (void*)wksp->dtable;
+                FSE_DTableHeader* DTableH = (FSE_DTableHeader*)(ptr);
+                uint fastMode = DTableH->fastMode;
+
+                if (fastMode != 0)
+                {
+                    return FSE_decompress_usingDTable_generic(dst, dstCapacity, (void*)ip, cSrcSize, (uint*)wksp->dtable, 1);
+                }
+
+                return FSE_decompress_usingDTable_generic(dst, dstCapacity, (void*)ip, cSrcSize, (uint*)wksp->dtable, 0);
+            }
+        }
+
+        /* Avoids the FORCE_INLINE of the _body() function. */
+        private static nuint FSE_decompress_wksp_body_default(void* dst, nuint dstCapacity, void* cSrc, nuint cSrcSize, uint maxLog, void* workSpace, nuint wkspSize)
+        {
+            return FSE_decompress_wksp_body(dst, dstCapacity, cSrc, cSrcSize, maxLog, workSpace, wkspSize, 0);
+        }
+
+        private static nuint FSE_decompress_wksp_body_bmi2(void* dst, nuint dstCapacity, void* cSrc, nuint cSrcSize, uint maxLog, void* workSpace, nuint wkspSize)
+        {
+            return FSE_decompress_wksp_body(dst, dstCapacity, cSrc, cSrcSize, maxLog, workSpace, wkspSize, 1);
+        }
+
+        public static nuint FSE_decompress_wksp_bmi2(void* dst, nuint dstCapacity, void* cSrc, nuint cSrcSize, uint maxLog, void* workSpace, nuint wkspSize, int bmi2)
+        {
+            if (bmi2 != 0)
+            {
+                return FSE_decompress_wksp_body_bmi2(dst, dstCapacity, cSrc, cSrcSize, maxLog, workSpace, wkspSize);
+            }
+
+            return FSE_decompress_wksp_body_default(dst, dstCapacity, cSrc, cSrcSize, maxLog, workSpace, wkspSize);
+        }
+
+        /*! FSE_buildDTable():
+            Builds 'dt', which must be already allocated, using FSE_createDTable().
+            return : 0, or an errorCode, which can be tested using FSE_isError() */
+        public static nuint FSE_buildDTable(uint* dt, short* normalizedCounter, uint maxSymbolValue, uint tableLog)
+        {
+            uint* wksp = stackalloc uint[8322];
+
+            return FSE_buildDTable_wksp(dt, normalizedCounter, maxSymbolValue, tableLog, (void*)wksp, (nuint)(sizeof(uint) * 8322));
+        }
+
+        /*! FSE_decompress():
+            Decompress FSE data from buffer 'cSrc', of size 'cSrcSize',
+            into already allocated destination buffer 'dst', of size 'dstCapacity'.
+            @return : size of regenerated data (<= maxDstSize),
+                      or an error code, which can be tested using FSE_isError() .
+
+            ** Important ** : FSE_decompress() does not decompress non-compressible nor RLE data !!!
+            Why ? : making this distinction requires a header.
+            Header management is intentionally delegated to the user layer, which can better manage special cases.
+        */
+        public static nuint FSE_decompress(void* dst, nuint dstCapacity, void* cSrc, nuint cSrcSize)
+        {
+            uint* wksp = stackalloc uint[5380];
+
+            return FSE_decompress_wksp(dst, dstCapacity, cSrc, cSrcSize, (uint)((14 - 2)), (void*)wksp, (nuint)(sizeof(uint) * 5380));
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HIST_checkInput_e.cs

@@ -0,0 +1,10 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public enum HIST_checkInput_e
+    {
+        trustInput,
+        checkMaxSymbolValue,
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_CElt_s.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /* static allocation of HUF's Compression Table */
+    /* this is a private definition, just exposed for allocation and strict aliasing purpose. never EVER access its members directly */
+    public partial struct HUF_CElt_s
+    {
+        public ushort val;
+
+        public byte nbBits;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_CompressWeightsWksp.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public unsafe partial struct HUF_CompressWeightsWksp
+    {
+        public fixed uint CTable[59];
+
+        public fixed uint scratchBuffer[30];
+
+        public fixed uint count[13];
+
+        public fixed short norm[13];
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_DEltX1.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /*-***************************/
+    /*  single-symbol decoding   */
+    /*-***************************/
+    public partial struct HUF_DEltX1
+    {
+        /* single-symbol decoding */
+        public byte @byte;
+
+        /* single-symbol decoding */
+        public byte nbBits;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_DEltX2.cs

@@ -0,0 +1,19 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /* *************************/
+    /* double-symbols decoding */
+    /* *************************/
+    public partial struct HUF_DEltX2
+    {
+        /* double-symbols decoding */
+        public ushort sequence;
+
+        /* double-symbols decoding */
+        public byte nbBits;
+
+        /* double-symbols decoding */
+        public byte length;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_ReadDTableX1_Workspace.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public unsafe partial struct HUF_ReadDTableX1_Workspace
+    {
+        public fixed uint rankVal[16];
+
+        public fixed uint rankStart[16];
+
+        public fixed uint statsWksp[218];
+
+        public fixed byte symbols[256];
+
+        public fixed byte huffWeight[256];
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_ReadDTableX2_Workspace.cs

@@ -0,0 +1,389 @@
+using InlineIL;
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using static InlineIL.IL.Emit;
+
+namespace ZstdSharp.Unsafe
+{
+    public unsafe partial struct HUF_ReadDTableX2_Workspace
+    {
+        public _rankVal_e__FixedBuffer rankVal;
+
+        public fixed uint rankStats[13];
+
+        public fixed uint rankStart0[14];
+
+        public _sortedSymbol_e__FixedBuffer sortedSymbol;
+
+        public fixed byte weightList[256];
+
+        public fixed uint calleeWksp[218];
+
+        public unsafe partial struct _rankVal_e__FixedBuffer
+        {
+            public rankValCol_t e0;
+            public rankValCol_t e1;
+            public rankValCol_t e2;
+            public rankValCol_t e3;
+            public rankValCol_t e4;
+            public rankValCol_t e5;
+            public rankValCol_t e6;
+            public rankValCol_t e7;
+            public rankValCol_t e8;
+            public rankValCol_t e9;
+            public rankValCol_t e10;
+            public rankValCol_t e11;
+
+            public ref rankValCol_t this[int index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + (uint)index);
+            }
+
+            public ref rankValCol_t this[uint index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + index);
+            }
+
+            public ref rankValCol_t this[nuint index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + (uint)index);
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            [InlineMethod.Inline]
+            public static implicit operator rankValCol_t*(in _rankVal_e__FixedBuffer t)
+            {
+                Ldarg_0();
+                Ldflda(new FieldRef(typeof(_rankVal_e__FixedBuffer), nameof(e0)));
+                return IL.ReturnPointer<rankValCol_t>();
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            [InlineMethod.Inline]
+            public static rankValCol_t* operator +(in _rankVal_e__FixedBuffer t, uint index)
+            {
+                Ldarg_0();
+                Ldflda(new FieldRef(typeof(_rankVal_e__FixedBuffer), nameof(e0)));
+                Ldarg_1();
+                Conv_I();
+                Sizeof<rankValCol_t>();
+                Conv_I();
+                Mul();
+                Add();
+                return IL.ReturnPointer<rankValCol_t>();
+            }
+        }
+
+        public unsafe partial struct _sortedSymbol_e__FixedBuffer
+        {
+            public sortedSymbol_t e0;
+            public sortedSymbol_t e1;
+            public sortedSymbol_t e2;
+            public sortedSymbol_t e3;
+            public sortedSymbol_t e4;
+            public sortedSymbol_t e5;
+            public sortedSymbol_t e6;
+            public sortedSymbol_t e7;
+            public sortedSymbol_t e8;
+            public sortedSymbol_t e9;
+            public sortedSymbol_t e10;
+            public sortedSymbol_t e11;
+            public sortedSymbol_t e12;
+            public sortedSymbol_t e13;
+            public sortedSymbol_t e14;
+            public sortedSymbol_t e15;
+            public sortedSymbol_t e16;
+            public sortedSymbol_t e17;
+            public sortedSymbol_t e18;
+            public sortedSymbol_t e19;
+            public sortedSymbol_t e20;
+            public sortedSymbol_t e21;
+            public sortedSymbol_t e22;
+            public sortedSymbol_t e23;
+            public sortedSymbol_t e24;
+            public sortedSymbol_t e25;
+            public sortedSymbol_t e26;
+            public sortedSymbol_t e27;
+            public sortedSymbol_t e28;
+            public sortedSymbol_t e29;
+            public sortedSymbol_t e30;
+            public sortedSymbol_t e31;
+            public sortedSymbol_t e32;
+            public sortedSymbol_t e33;
+            public sortedSymbol_t e34;
+            public sortedSymbol_t e35;
+            public sortedSymbol_t e36;
+            public sortedSymbol_t e37;
+            public sortedSymbol_t e38;
+            public sortedSymbol_t e39;
+            public sortedSymbol_t e40;
+            public sortedSymbol_t e41;
+            public sortedSymbol_t e42;
+            public sortedSymbol_t e43;
+            public sortedSymbol_t e44;
+            public sortedSymbol_t e45;
+            public sortedSymbol_t e46;
+            public sortedSymbol_t e47;
+            public sortedSymbol_t e48;
+            public sortedSymbol_t e49;
+            public sortedSymbol_t e50;
+            public sortedSymbol_t e51;
+            public sortedSymbol_t e52;
+            public sortedSymbol_t e53;
+            public sortedSymbol_t e54;
+            public sortedSymbol_t e55;
+            public sortedSymbol_t e56;
+            public sortedSymbol_t e57;
+            public sortedSymbol_t e58;
+            public sortedSymbol_t e59;
+            public sortedSymbol_t e60;
+            public sortedSymbol_t e61;
+            public sortedSymbol_t e62;
+            public sortedSymbol_t e63;
+            public sortedSymbol_t e64;
+            public sortedSymbol_t e65;
+            public sortedSymbol_t e66;
+            public sortedSymbol_t e67;
+            public sortedSymbol_t e68;
+            public sortedSymbol_t e69;
+            public sortedSymbol_t e70;
+            public sortedSymbol_t e71;
+            public sortedSymbol_t e72;
+            public sortedSymbol_t e73;
+            public sortedSymbol_t e74;
+            public sortedSymbol_t e75;
+            public sortedSymbol_t e76;
+            public sortedSymbol_t e77;
+            public sortedSymbol_t e78;
+            public sortedSymbol_t e79;
+            public sortedSymbol_t e80;
+            public sortedSymbol_t e81;
+            public sortedSymbol_t e82;
+            public sortedSymbol_t e83;
+            public sortedSymbol_t e84;
+            public sortedSymbol_t e85;
+            public sortedSymbol_t e86;
+            public sortedSymbol_t e87;
+            public sortedSymbol_t e88;
+            public sortedSymbol_t e89;
+            public sortedSymbol_t e90;
+            public sortedSymbol_t e91;
+            public sortedSymbol_t e92;
+            public sortedSymbol_t e93;
+            public sortedSymbol_t e94;
+            public sortedSymbol_t e95;
+            public sortedSymbol_t e96;
+            public sortedSymbol_t e97;
+            public sortedSymbol_t e98;
+            public sortedSymbol_t e99;
+            public sortedSymbol_t e100;
+            public sortedSymbol_t e101;
+            public sortedSymbol_t e102;
+            public sortedSymbol_t e103;
+            public sortedSymbol_t e104;
+            public sortedSymbol_t e105;
+            public sortedSymbol_t e106;
+            public sortedSymbol_t e107;
+            public sortedSymbol_t e108;
+            public sortedSymbol_t e109;
+            public sortedSymbol_t e110;
+            public sortedSymbol_t e111;
+            public sortedSymbol_t e112;
+            public sortedSymbol_t e113;
+            public sortedSymbol_t e114;
+            public sortedSymbol_t e115;
+            public sortedSymbol_t e116;
+            public sortedSymbol_t e117;
+            public sortedSymbol_t e118;
+            public sortedSymbol_t e119;
+            public sortedSymbol_t e120;
+            public sortedSymbol_t e121;
+            public sortedSymbol_t e122;
+            public sortedSymbol_t e123;
+            public sortedSymbol_t e124;
+            public sortedSymbol_t e125;
+            public sortedSymbol_t e126;
+            public sortedSymbol_t e127;
+            public sortedSymbol_t e128;
+            public sortedSymbol_t e129;
+            public sortedSymbol_t e130;
+            public sortedSymbol_t e131;
+            public sortedSymbol_t e132;
+            public sortedSymbol_t e133;
+            public sortedSymbol_t e134;
+            public sortedSymbol_t e135;
+            public sortedSymbol_t e136;
+            public sortedSymbol_t e137;
+            public sortedSymbol_t e138;
+            public sortedSymbol_t e139;
+            public sortedSymbol_t e140;
+            public sortedSymbol_t e141;
+            public sortedSymbol_t e142;
+            public sortedSymbol_t e143;
+            public sortedSymbol_t e144;
+            public sortedSymbol_t e145;
+            public sortedSymbol_t e146;
+            public sortedSymbol_t e147;
+            public sortedSymbol_t e148;
+            public sortedSymbol_t e149;
+            public sortedSymbol_t e150;
+            public sortedSymbol_t e151;
+            public sortedSymbol_t e152;
+            public sortedSymbol_t e153;
+            public sortedSymbol_t e154;
+            public sortedSymbol_t e155;
+            public sortedSymbol_t e156;
+            public sortedSymbol_t e157;
+            public sortedSymbol_t e158;
+            public sortedSymbol_t e159;
+            public sortedSymbol_t e160;
+            public sortedSymbol_t e161;
+            public sortedSymbol_t e162;
+            public sortedSymbol_t e163;
+            public sortedSymbol_t e164;
+            public sortedSymbol_t e165;
+            public sortedSymbol_t e166;
+            public sortedSymbol_t e167;
+            public sortedSymbol_t e168;
+            public sortedSymbol_t e169;
+            public sortedSymbol_t e170;
+            public sortedSymbol_t e171;
+            public sortedSymbol_t e172;
+            public sortedSymbol_t e173;
+            public sortedSymbol_t e174;
+            public sortedSymbol_t e175;
+            public sortedSymbol_t e176;
+            public sortedSymbol_t e177;
+            public sortedSymbol_t e178;
+            public sortedSymbol_t e179;
+            public sortedSymbol_t e180;
+            public sortedSymbol_t e181;
+            public sortedSymbol_t e182;
+            public sortedSymbol_t e183;
+            public sortedSymbol_t e184;
+            public sortedSymbol_t e185;
+            public sortedSymbol_t e186;
+            public sortedSymbol_t e187;
+            public sortedSymbol_t e188;
+            public sortedSymbol_t e189;
+            public sortedSymbol_t e190;
+            public sortedSymbol_t e191;
+            public sortedSymbol_t e192;
+            public sortedSymbol_t e193;
+            public sortedSymbol_t e194;
+            public sortedSymbol_t e195;
+            public sortedSymbol_t e196;
+            public sortedSymbol_t e197;
+            public sortedSymbol_t e198;
+            public sortedSymbol_t e199;
+            public sortedSymbol_t e200;
+            public sortedSymbol_t e201;
+            public sortedSymbol_t e202;
+            public sortedSymbol_t e203;
+            public sortedSymbol_t e204;
+            public sortedSymbol_t e205;
+            public sortedSymbol_t e206;
+            public sortedSymbol_t e207;
+            public sortedSymbol_t e208;
+            public sortedSymbol_t e209;
+            public sortedSymbol_t e210;
+            public sortedSymbol_t e211;
+            public sortedSymbol_t e212;
+            public sortedSymbol_t e213;
+            public sortedSymbol_t e214;
+            public sortedSymbol_t e215;
+            public sortedSymbol_t e216;
+            public sortedSymbol_t e217;
+            public sortedSymbol_t e218;
+            public sortedSymbol_t e219;
+            public sortedSymbol_t e220;
+            public sortedSymbol_t e221;
+            public sortedSymbol_t e222;
+            public sortedSymbol_t e223;
+            public sortedSymbol_t e224;
+            public sortedSymbol_t e225;
+            public sortedSymbol_t e226;
+            public sortedSymbol_t e227;
+            public sortedSymbol_t e228;
+            public sortedSymbol_t e229;
+            public sortedSymbol_t e230;
+            public sortedSymbol_t e231;
+            public sortedSymbol_t e232;
+            public sortedSymbol_t e233;
+            public sortedSymbol_t e234;
+            public sortedSymbol_t e235;
+            public sortedSymbol_t e236;
+            public sortedSymbol_t e237;
+            public sortedSymbol_t e238;
+            public sortedSymbol_t e239;
+            public sortedSymbol_t e240;
+            public sortedSymbol_t e241;
+            public sortedSymbol_t e242;
+            public sortedSymbol_t e243;
+            public sortedSymbol_t e244;
+            public sortedSymbol_t e245;
+            public sortedSymbol_t e246;
+            public sortedSymbol_t e247;
+            public sortedSymbol_t e248;
+            public sortedSymbol_t e249;
+            public sortedSymbol_t e250;
+            public sortedSymbol_t e251;
+            public sortedSymbol_t e252;
+            public sortedSymbol_t e253;
+            public sortedSymbol_t e254;
+            public sortedSymbol_t e255;
+
+            public ref sortedSymbol_t this[int index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + (uint)index);
+            }
+
+            public ref sortedSymbol_t this[uint index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + index);
+            }
+
+            public ref sortedSymbol_t this[nuint index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + (uint)index);
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            [InlineMethod.Inline]
+            public static implicit operator sortedSymbol_t*(in _sortedSymbol_e__FixedBuffer t)
+            {
+                Ldarg_0();
+                Ldflda(new FieldRef(typeof(_sortedSymbol_e__FixedBuffer), nameof(e0)));
+                return IL.ReturnPointer<sortedSymbol_t>();
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            [InlineMethod.Inline]
+            public static sortedSymbol_t* operator +(in _sortedSymbol_e__FixedBuffer t, uint index)
+            {
+                Ldarg_0();
+                Ldflda(new FieldRef(typeof(_sortedSymbol_e__FixedBuffer), nameof(e0)));
+                Ldarg_1();
+                Conv_I();
+                Sizeof<sortedSymbol_t>();
+                Conv_I();
+                Mul();
+                Add();
+                return IL.ReturnPointer<sortedSymbol_t>();
+            }
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_WriteCTableWksp.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public unsafe partial struct HUF_WriteCTableWksp
+    {
+        public HUF_CompressWeightsWksp wksp;
+
+        /* precomputed conversion table */
+        public fixed byte bitsToWeight[13];
+
+        public fixed byte huffWeight[255];
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_buildCTable_wksp_tables.cs

@@ -0,0 +1,657 @@
+using InlineIL;
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using static InlineIL.IL.Emit;
+
+namespace ZstdSharp.Unsafe
+{
+    public partial struct HUF_buildCTable_wksp_tables
+    {
+        public _huffNodeTbl_e__FixedBuffer huffNodeTbl;
+
+        public _rankPosition_e__FixedBuffer rankPosition;
+
+        public unsafe partial struct _huffNodeTbl_e__FixedBuffer
+        {
+            public nodeElt_s e0;
+            public nodeElt_s e1;
+            public nodeElt_s e2;
+            public nodeElt_s e3;
+            public nodeElt_s e4;
+            public nodeElt_s e5;
+            public nodeElt_s e6;
+            public nodeElt_s e7;
+            public nodeElt_s e8;
+            public nodeElt_s e9;
+            public nodeElt_s e10;
+            public nodeElt_s e11;
+            public nodeElt_s e12;
+            public nodeElt_s e13;
+            public nodeElt_s e14;
+            public nodeElt_s e15;
+            public nodeElt_s e16;
+            public nodeElt_s e17;
+            public nodeElt_s e18;
+            public nodeElt_s e19;
+            public nodeElt_s e20;
+            public nodeElt_s e21;
+            public nodeElt_s e22;
+            public nodeElt_s e23;
+            public nodeElt_s e24;
+            public nodeElt_s e25;
+            public nodeElt_s e26;
+            public nodeElt_s e27;
+            public nodeElt_s e28;
+            public nodeElt_s e29;
+            public nodeElt_s e30;
+            public nodeElt_s e31;
+            public nodeElt_s e32;
+            public nodeElt_s e33;
+            public nodeElt_s e34;
+            public nodeElt_s e35;
+            public nodeElt_s e36;
+            public nodeElt_s e37;
+            public nodeElt_s e38;
+            public nodeElt_s e39;
+            public nodeElt_s e40;
+            public nodeElt_s e41;
+            public nodeElt_s e42;
+            public nodeElt_s e43;
+            public nodeElt_s e44;
+            public nodeElt_s e45;
+            public nodeElt_s e46;
+            public nodeElt_s e47;
+            public nodeElt_s e48;
+            public nodeElt_s e49;
+            public nodeElt_s e50;
+            public nodeElt_s e51;
+            public nodeElt_s e52;
+            public nodeElt_s e53;
+            public nodeElt_s e54;
+            public nodeElt_s e55;
+            public nodeElt_s e56;
+            public nodeElt_s e57;
+            public nodeElt_s e58;
+            public nodeElt_s e59;
+            public nodeElt_s e60;
+            public nodeElt_s e61;
+            public nodeElt_s e62;
+            public nodeElt_s e63;
+            public nodeElt_s e64;
+            public nodeElt_s e65;
+            public nodeElt_s e66;
+            public nodeElt_s e67;
+            public nodeElt_s e68;
+            public nodeElt_s e69;
+            public nodeElt_s e70;
+            public nodeElt_s e71;
+            public nodeElt_s e72;
+            public nodeElt_s e73;
+            public nodeElt_s e74;
+            public nodeElt_s e75;
+            public nodeElt_s e76;
+            public nodeElt_s e77;
+            public nodeElt_s e78;
+            public nodeElt_s e79;
+            public nodeElt_s e80;
+            public nodeElt_s e81;
+            public nodeElt_s e82;
+            public nodeElt_s e83;
+            public nodeElt_s e84;
+            public nodeElt_s e85;
+            public nodeElt_s e86;
+            public nodeElt_s e87;
+            public nodeElt_s e88;
+            public nodeElt_s e89;
+            public nodeElt_s e90;
+            public nodeElt_s e91;
+            public nodeElt_s e92;
+            public nodeElt_s e93;
+            public nodeElt_s e94;
+            public nodeElt_s e95;
+            public nodeElt_s e96;
+            public nodeElt_s e97;
+            public nodeElt_s e98;
+            public nodeElt_s e99;
+            public nodeElt_s e100;
+            public nodeElt_s e101;
+            public nodeElt_s e102;
+            public nodeElt_s e103;
+            public nodeElt_s e104;
+            public nodeElt_s e105;
+            public nodeElt_s e106;
+            public nodeElt_s e107;
+            public nodeElt_s e108;
+            public nodeElt_s e109;
+            public nodeElt_s e110;
+            public nodeElt_s e111;
+            public nodeElt_s e112;
+            public nodeElt_s e113;
+            public nodeElt_s e114;
+            public nodeElt_s e115;
+            public nodeElt_s e116;
+            public nodeElt_s e117;
+            public nodeElt_s e118;
+            public nodeElt_s e119;
+            public nodeElt_s e120;
+            public nodeElt_s e121;
+            public nodeElt_s e122;
+            public nodeElt_s e123;
+            public nodeElt_s e124;
+            public nodeElt_s e125;
+            public nodeElt_s e126;
+            public nodeElt_s e127;
+            public nodeElt_s e128;
+            public nodeElt_s e129;
+            public nodeElt_s e130;
+            public nodeElt_s e131;
+            public nodeElt_s e132;
+            public nodeElt_s e133;
+            public nodeElt_s e134;
+            public nodeElt_s e135;
+            public nodeElt_s e136;
+            public nodeElt_s e137;
+            public nodeElt_s e138;
+            public nodeElt_s e139;
+            public nodeElt_s e140;
+            public nodeElt_s e141;
+            public nodeElt_s e142;
+            public nodeElt_s e143;
+            public nodeElt_s e144;
+            public nodeElt_s e145;
+            public nodeElt_s e146;
+            public nodeElt_s e147;
+            public nodeElt_s e148;
+            public nodeElt_s e149;
+            public nodeElt_s e150;
+            public nodeElt_s e151;
+            public nodeElt_s e152;
+            public nodeElt_s e153;
+            public nodeElt_s e154;
+            public nodeElt_s e155;
+            public nodeElt_s e156;
+            public nodeElt_s e157;
+            public nodeElt_s e158;
+            public nodeElt_s e159;
+            public nodeElt_s e160;
+            public nodeElt_s e161;
+            public nodeElt_s e162;
+            public nodeElt_s e163;
+            public nodeElt_s e164;
+            public nodeElt_s e165;
+            public nodeElt_s e166;
+            public nodeElt_s e167;
+            public nodeElt_s e168;
+            public nodeElt_s e169;
+            public nodeElt_s e170;
+            public nodeElt_s e171;
+            public nodeElt_s e172;
+            public nodeElt_s e173;
+            public nodeElt_s e174;
+            public nodeElt_s e175;
+            public nodeElt_s e176;
+            public nodeElt_s e177;
+            public nodeElt_s e178;
+            public nodeElt_s e179;
+            public nodeElt_s e180;
+            public nodeElt_s e181;
+            public nodeElt_s e182;
+            public nodeElt_s e183;
+            public nodeElt_s e184;
+            public nodeElt_s e185;
+            public nodeElt_s e186;
+            public nodeElt_s e187;
+            public nodeElt_s e188;
+            public nodeElt_s e189;
+            public nodeElt_s e190;
+            public nodeElt_s e191;
+            public nodeElt_s e192;
+            public nodeElt_s e193;
+            public nodeElt_s e194;
+            public nodeElt_s e195;
+            public nodeElt_s e196;
+            public nodeElt_s e197;
+            public nodeElt_s e198;
+            public nodeElt_s e199;
+            public nodeElt_s e200;
+            public nodeElt_s e201;
+            public nodeElt_s e202;
+            public nodeElt_s e203;
+            public nodeElt_s e204;
+            public nodeElt_s e205;
+            public nodeElt_s e206;
+            public nodeElt_s e207;
+            public nodeElt_s e208;
+            public nodeElt_s e209;
+            public nodeElt_s e210;
+            public nodeElt_s e211;
+            public nodeElt_s e212;
+            public nodeElt_s e213;
+            public nodeElt_s e214;
+            public nodeElt_s e215;
+            public nodeElt_s e216;
+            public nodeElt_s e217;
+            public nodeElt_s e218;
+            public nodeElt_s e219;
+            public nodeElt_s e220;
+            public nodeElt_s e221;
+            public nodeElt_s e222;
+            public nodeElt_s e223;
+            public nodeElt_s e224;
+            public nodeElt_s e225;
+            public nodeElt_s e226;
+            public nodeElt_s e227;
+            public nodeElt_s e228;
+            public nodeElt_s e229;
+            public nodeElt_s e230;
+            public nodeElt_s e231;
+            public nodeElt_s e232;
+            public nodeElt_s e233;
+            public nodeElt_s e234;
+            public nodeElt_s e235;
+            public nodeElt_s e236;
+            public nodeElt_s e237;
+            public nodeElt_s e238;
+            public nodeElt_s e239;
+            public nodeElt_s e240;
+            public nodeElt_s e241;
+            public nodeElt_s e242;
+            public nodeElt_s e243;
+            public nodeElt_s e244;
+            public nodeElt_s e245;
+            public nodeElt_s e246;
+            public nodeElt_s e247;
+            public nodeElt_s e248;
+            public nodeElt_s e249;
+            public nodeElt_s e250;
+            public nodeElt_s e251;
+            public nodeElt_s e252;
+            public nodeElt_s e253;
+            public nodeElt_s e254;
+            public nodeElt_s e255;
+            public nodeElt_s e256;
+            public nodeElt_s e257;
+            public nodeElt_s e258;
+            public nodeElt_s e259;
+            public nodeElt_s e260;
+            public nodeElt_s e261;
+            public nodeElt_s e262;
+            public nodeElt_s e263;
+            public nodeElt_s e264;
+            public nodeElt_s e265;
+            public nodeElt_s e266;
+            public nodeElt_s e267;
+            public nodeElt_s e268;
+            public nodeElt_s e269;
+            public nodeElt_s e270;
+            public nodeElt_s e271;
+            public nodeElt_s e272;
+            public nodeElt_s e273;
+            public nodeElt_s e274;
+            public nodeElt_s e275;
+            public nodeElt_s e276;
+            public nodeElt_s e277;
+            public nodeElt_s e278;
+            public nodeElt_s e279;
+            public nodeElt_s e280;
+            public nodeElt_s e281;
+            public nodeElt_s e282;
+            public nodeElt_s e283;
+            public nodeElt_s e284;
+            public nodeElt_s e285;
+            public nodeElt_s e286;
+            public nodeElt_s e287;
+            public nodeElt_s e288;
+            public nodeElt_s e289;
+            public nodeElt_s e290;
+            public nodeElt_s e291;
+            public nodeElt_s e292;
+            public nodeElt_s e293;
+            public nodeElt_s e294;
+            public nodeElt_s e295;
+            public nodeElt_s e296;
+            public nodeElt_s e297;
+            public nodeElt_s e298;
+            public nodeElt_s e299;
+            public nodeElt_s e300;
+            public nodeElt_s e301;
+            public nodeElt_s e302;
+            public nodeElt_s e303;
+            public nodeElt_s e304;
+            public nodeElt_s e305;
+            public nodeElt_s e306;
+            public nodeElt_s e307;
+            public nodeElt_s e308;
+            public nodeElt_s e309;
+            public nodeElt_s e310;
+            public nodeElt_s e311;
+            public nodeElt_s e312;
+            public nodeElt_s e313;
+            public nodeElt_s e314;
+            public nodeElt_s e315;
+            public nodeElt_s e316;
+            public nodeElt_s e317;
+            public nodeElt_s e318;
+            public nodeElt_s e319;
+            public nodeElt_s e320;
+            public nodeElt_s e321;
+            public nodeElt_s e322;
+            public nodeElt_s e323;
+            public nodeElt_s e324;
+            public nodeElt_s e325;
+            public nodeElt_s e326;
+            public nodeElt_s e327;
+            public nodeElt_s e328;
+            public nodeElt_s e329;
+            public nodeElt_s e330;
+            public nodeElt_s e331;
+            public nodeElt_s e332;
+            public nodeElt_s e333;
+            public nodeElt_s e334;
+            public nodeElt_s e335;
+            public nodeElt_s e336;
+            public nodeElt_s e337;
+            public nodeElt_s e338;
+            public nodeElt_s e339;
+            public nodeElt_s e340;
+            public nodeElt_s e341;
+            public nodeElt_s e342;
+            public nodeElt_s e343;
+            public nodeElt_s e344;
+            public nodeElt_s e345;
+            public nodeElt_s e346;
+            public nodeElt_s e347;
+            public nodeElt_s e348;
+            public nodeElt_s e349;
+            public nodeElt_s e350;
+            public nodeElt_s e351;
+            public nodeElt_s e352;
+            public nodeElt_s e353;
+            public nodeElt_s e354;
+            public nodeElt_s e355;
+            public nodeElt_s e356;
+            public nodeElt_s e357;
+            public nodeElt_s e358;
+            public nodeElt_s e359;
+            public nodeElt_s e360;
+            public nodeElt_s e361;
+            public nodeElt_s e362;
+            public nodeElt_s e363;
+            public nodeElt_s e364;
+            public nodeElt_s e365;
+            public nodeElt_s e366;
+            public nodeElt_s e367;
+            public nodeElt_s e368;
+            public nodeElt_s e369;
+            public nodeElt_s e370;
+            public nodeElt_s e371;
+            public nodeElt_s e372;
+            public nodeElt_s e373;
+            public nodeElt_s e374;
+            public nodeElt_s e375;
+            public nodeElt_s e376;
+            public nodeElt_s e377;
+            public nodeElt_s e378;
+            public nodeElt_s e379;
+            public nodeElt_s e380;
+            public nodeElt_s e381;
+            public nodeElt_s e382;
+            public nodeElt_s e383;
+            public nodeElt_s e384;
+            public nodeElt_s e385;
+            public nodeElt_s e386;
+            public nodeElt_s e387;
+            public nodeElt_s e388;
+            public nodeElt_s e389;
+            public nodeElt_s e390;
+            public nodeElt_s e391;
+            public nodeElt_s e392;
+            public nodeElt_s e393;
+            public nodeElt_s e394;
+            public nodeElt_s e395;
+            public nodeElt_s e396;
+            public nodeElt_s e397;
+            public nodeElt_s e398;
+            public nodeElt_s e399;
+            public nodeElt_s e400;
+            public nodeElt_s e401;
+            public nodeElt_s e402;
+            public nodeElt_s e403;
+            public nodeElt_s e404;
+            public nodeElt_s e405;
+            public nodeElt_s e406;
+            public nodeElt_s e407;
+            public nodeElt_s e408;
+            public nodeElt_s e409;
+            public nodeElt_s e410;
+            public nodeElt_s e411;
+            public nodeElt_s e412;
+            public nodeElt_s e413;
+            public nodeElt_s e414;
+            public nodeElt_s e415;
+            public nodeElt_s e416;
+            public nodeElt_s e417;
+            public nodeElt_s e418;
+            public nodeElt_s e419;
+            public nodeElt_s e420;
+            public nodeElt_s e421;
+            public nodeElt_s e422;
+            public nodeElt_s e423;
+            public nodeElt_s e424;
+            public nodeElt_s e425;
+            public nodeElt_s e426;
+            public nodeElt_s e427;
+            public nodeElt_s e428;
+            public nodeElt_s e429;
+            public nodeElt_s e430;
+            public nodeElt_s e431;
+            public nodeElt_s e432;
+            public nodeElt_s e433;
+            public nodeElt_s e434;
+            public nodeElt_s e435;
+            public nodeElt_s e436;
+            public nodeElt_s e437;
+            public nodeElt_s e438;
+            public nodeElt_s e439;
+            public nodeElt_s e440;
+            public nodeElt_s e441;
+            public nodeElt_s e442;
+            public nodeElt_s e443;
+            public nodeElt_s e444;
+            public nodeElt_s e445;
+            public nodeElt_s e446;
+            public nodeElt_s e447;
+            public nodeElt_s e448;
+            public nodeElt_s e449;
+            public nodeElt_s e450;
+            public nodeElt_s e451;
+            public nodeElt_s e452;
+            public nodeElt_s e453;
+            public nodeElt_s e454;
+            public nodeElt_s e455;
+            public nodeElt_s e456;
+            public nodeElt_s e457;
+            public nodeElt_s e458;
+            public nodeElt_s e459;
+            public nodeElt_s e460;
+            public nodeElt_s e461;
+            public nodeElt_s e462;
+            public nodeElt_s e463;
+            public nodeElt_s e464;
+            public nodeElt_s e465;
+            public nodeElt_s e466;
+            public nodeElt_s e467;
+            public nodeElt_s e468;
+            public nodeElt_s e469;
+            public nodeElt_s e470;
+            public nodeElt_s e471;
+            public nodeElt_s e472;
+            public nodeElt_s e473;
+            public nodeElt_s e474;
+            public nodeElt_s e475;
+            public nodeElt_s e476;
+            public nodeElt_s e477;
+            public nodeElt_s e478;
+            public nodeElt_s e479;
+            public nodeElt_s e480;
+            public nodeElt_s e481;
+            public nodeElt_s e482;
+            public nodeElt_s e483;
+            public nodeElt_s e484;
+            public nodeElt_s e485;
+            public nodeElt_s e486;
+            public nodeElt_s e487;
+            public nodeElt_s e488;
+            public nodeElt_s e489;
+            public nodeElt_s e490;
+            public nodeElt_s e491;
+            public nodeElt_s e492;
+            public nodeElt_s e493;
+            public nodeElt_s e494;
+            public nodeElt_s e495;
+            public nodeElt_s e496;
+            public nodeElt_s e497;
+            public nodeElt_s e498;
+            public nodeElt_s e499;
+            public nodeElt_s e500;
+            public nodeElt_s e501;
+            public nodeElt_s e502;
+            public nodeElt_s e503;
+            public nodeElt_s e504;
+            public nodeElt_s e505;
+            public nodeElt_s e506;
+            public nodeElt_s e507;
+            public nodeElt_s e508;
+            public nodeElt_s e509;
+            public nodeElt_s e510;
+            public nodeElt_s e511;
+
+            public ref nodeElt_s this[int index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + (uint)index);
+            }
+
+            public ref nodeElt_s this[uint index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + index);
+            }
+
+            public ref nodeElt_s this[nuint index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + (uint)index);
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            [InlineMethod.Inline]
+            public static implicit operator nodeElt_s*(in _huffNodeTbl_e__FixedBuffer t)
+            {
+                Ldarg_0();
+                Ldflda(new FieldRef(typeof(_huffNodeTbl_e__FixedBuffer), nameof(e0)));
+                return IL.ReturnPointer<nodeElt_s>();
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            [InlineMethod.Inline]
+            public static nodeElt_s* operator +(in _huffNodeTbl_e__FixedBuffer t, uint index)
+            {
+                Ldarg_0();
+                Ldflda(new FieldRef(typeof(_huffNodeTbl_e__FixedBuffer), nameof(e0)));
+                Ldarg_1();
+                Conv_I();
+                Sizeof<nodeElt_s>();
+                Conv_I();
+                Mul();
+                Add();
+                return IL.ReturnPointer<nodeElt_s>();
+            }
+        }
+
+        public unsafe partial struct _rankPosition_e__FixedBuffer
+        {
+            public rankPos e0;
+            public rankPos e1;
+            public rankPos e2;
+            public rankPos e3;
+            public rankPos e4;
+            public rankPos e5;
+            public rankPos e6;
+            public rankPos e7;
+            public rankPos e8;
+            public rankPos e9;
+            public rankPos e10;
+            public rankPos e11;
+            public rankPos e12;
+            public rankPos e13;
+            public rankPos e14;
+            public rankPos e15;
+            public rankPos e16;
+            public rankPos e17;
+            public rankPos e18;
+            public rankPos e19;
+            public rankPos e20;
+            public rankPos e21;
+            public rankPos e22;
+            public rankPos e23;
+            public rankPos e24;
+            public rankPos e25;
+            public rankPos e26;
+            public rankPos e27;
+            public rankPos e28;
+            public rankPos e29;
+            public rankPos e30;
+            public rankPos e31;
+
+            public ref rankPos this[int index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + (uint)index);
+            }
+
+            public ref rankPos this[uint index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + index);
+            }
+
+            public ref rankPos this[nuint index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + (uint)index);
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            [InlineMethod.Inline]
+            public static implicit operator rankPos*(in _rankPosition_e__FixedBuffer t)
+            {
+                Ldarg_0();
+                Ldflda(new FieldRef(typeof(_rankPosition_e__FixedBuffer), nameof(e0)));
+                return IL.ReturnPointer<rankPos>();
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            [InlineMethod.Inline]
+            public static rankPos* operator +(in _rankPosition_e__FixedBuffer t, uint index)
+            {
+                Ldarg_0();
+                Ldflda(new FieldRef(typeof(_rankPosition_e__FixedBuffer), nameof(e0)));
+                Ldarg_1();
+                Conv_I();
+                Sizeof<rankPos>();
+                Conv_I();
+                Mul();
+                Add();
+                return IL.ReturnPointer<rankPos>();
+            }
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_compress_tables_t.cs

@@ -0,0 +1,322 @@
+using InlineIL;
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using static InlineIL.IL.Emit;
+
+namespace ZstdSharp.Unsafe
+{
+    public unsafe partial struct HUF_compress_tables_t
+    {
+        public fixed uint count[256];
+
+        public _CTable_e__FixedBuffer CTable;
+
+        public _wksps_e__Union wksps;
+
+        public unsafe partial struct _CTable_e__FixedBuffer
+        {
+            public HUF_CElt_s e0;
+            public HUF_CElt_s e1;
+            public HUF_CElt_s e2;
+            public HUF_CElt_s e3;
+            public HUF_CElt_s e4;
+            public HUF_CElt_s e5;
+            public HUF_CElt_s e6;
+            public HUF_CElt_s e7;
+            public HUF_CElt_s e8;
+            public HUF_CElt_s e9;
+            public HUF_CElt_s e10;
+            public HUF_CElt_s e11;
+            public HUF_CElt_s e12;
+            public HUF_CElt_s e13;
+            public HUF_CElt_s e14;
+            public HUF_CElt_s e15;
+            public HUF_CElt_s e16;
+            public HUF_CElt_s e17;
+            public HUF_CElt_s e18;
+            public HUF_CElt_s e19;
+            public HUF_CElt_s e20;
+            public HUF_CElt_s e21;
+            public HUF_CElt_s e22;
+            public HUF_CElt_s e23;
+            public HUF_CElt_s e24;
+            public HUF_CElt_s e25;
+            public HUF_CElt_s e26;
+            public HUF_CElt_s e27;
+            public HUF_CElt_s e28;
+            public HUF_CElt_s e29;
+            public HUF_CElt_s e30;
+            public HUF_CElt_s e31;
+            public HUF_CElt_s e32;
+            public HUF_CElt_s e33;
+            public HUF_CElt_s e34;
+            public HUF_CElt_s e35;
+            public HUF_CElt_s e36;
+            public HUF_CElt_s e37;
+            public HUF_CElt_s e38;
+            public HUF_CElt_s e39;
+            public HUF_CElt_s e40;
+            public HUF_CElt_s e41;
+            public HUF_CElt_s e42;
+            public HUF_CElt_s e43;
+            public HUF_CElt_s e44;
+            public HUF_CElt_s e45;
+            public HUF_CElt_s e46;
+            public HUF_CElt_s e47;
+            public HUF_CElt_s e48;
+            public HUF_CElt_s e49;
+            public HUF_CElt_s e50;
+            public HUF_CElt_s e51;
+            public HUF_CElt_s e52;
+            public HUF_CElt_s e53;
+            public HUF_CElt_s e54;
+            public HUF_CElt_s e55;
+            public HUF_CElt_s e56;
+            public HUF_CElt_s e57;
+            public HUF_CElt_s e58;
+            public HUF_CElt_s e59;
+            public HUF_CElt_s e60;
+            public HUF_CElt_s e61;
+            public HUF_CElt_s e62;
+            public HUF_CElt_s e63;
+            public HUF_CElt_s e64;
+            public HUF_CElt_s e65;
+            public HUF_CElt_s e66;
+            public HUF_CElt_s e67;
+            public HUF_CElt_s e68;
+            public HUF_CElt_s e69;
+            public HUF_CElt_s e70;
+            public HUF_CElt_s e71;
+            public HUF_CElt_s e72;
+            public HUF_CElt_s e73;
+            public HUF_CElt_s e74;
+            public HUF_CElt_s e75;
+            public HUF_CElt_s e76;
+            public HUF_CElt_s e77;
+            public HUF_CElt_s e78;
+            public HUF_CElt_s e79;
+            public HUF_CElt_s e80;
+            public HUF_CElt_s e81;
+            public HUF_CElt_s e82;
+            public HUF_CElt_s e83;
+            public HUF_CElt_s e84;
+            public HUF_CElt_s e85;
+            public HUF_CElt_s e86;
+            public HUF_CElt_s e87;
+            public HUF_CElt_s e88;
+            public HUF_CElt_s e89;
+            public HUF_CElt_s e90;
+            public HUF_CElt_s e91;
+            public HUF_CElt_s e92;
+            public HUF_CElt_s e93;
+            public HUF_CElt_s e94;
+            public HUF_CElt_s e95;
+            public HUF_CElt_s e96;
+            public HUF_CElt_s e97;
+            public HUF_CElt_s e98;
+            public HUF_CElt_s e99;
+            public HUF_CElt_s e100;
+            public HUF_CElt_s e101;
+            public HUF_CElt_s e102;
+            public HUF_CElt_s e103;
+            public HUF_CElt_s e104;
+            public HUF_CElt_s e105;
+            public HUF_CElt_s e106;
+            public HUF_CElt_s e107;
+            public HUF_CElt_s e108;
+            public HUF_CElt_s e109;
+            public HUF_CElt_s e110;
+            public HUF_CElt_s e111;
+            public HUF_CElt_s e112;
+            public HUF_CElt_s e113;
+            public HUF_CElt_s e114;
+            public HUF_CElt_s e115;
+            public HUF_CElt_s e116;
+            public HUF_CElt_s e117;
+            public HUF_CElt_s e118;
+            public HUF_CElt_s e119;
+            public HUF_CElt_s e120;
+            public HUF_CElt_s e121;
+            public HUF_CElt_s e122;
+            public HUF_CElt_s e123;
+            public HUF_CElt_s e124;
+            public HUF_CElt_s e125;
+            public HUF_CElt_s e126;
+            public HUF_CElt_s e127;
+            public HUF_CElt_s e128;
+            public HUF_CElt_s e129;
+            public HUF_CElt_s e130;
+            public HUF_CElt_s e131;
+            public HUF_CElt_s e132;
+            public HUF_CElt_s e133;
+            public HUF_CElt_s e134;
+            public HUF_CElt_s e135;
+            public HUF_CElt_s e136;
+            public HUF_CElt_s e137;
+            public HUF_CElt_s e138;
+            public HUF_CElt_s e139;
+            public HUF_CElt_s e140;
+            public HUF_CElt_s e141;
+            public HUF_CElt_s e142;
+            public HUF_CElt_s e143;
+            public HUF_CElt_s e144;
+            public HUF_CElt_s e145;
+            public HUF_CElt_s e146;
+            public HUF_CElt_s e147;
+            public HUF_CElt_s e148;
+            public HUF_CElt_s e149;
+            public HUF_CElt_s e150;
+            public HUF_CElt_s e151;
+            public HUF_CElt_s e152;
+            public HUF_CElt_s e153;
+            public HUF_CElt_s e154;
+            public HUF_CElt_s e155;
+            public HUF_CElt_s e156;
+            public HUF_CElt_s e157;
+            public HUF_CElt_s e158;
+            public HUF_CElt_s e159;
+            public HUF_CElt_s e160;
+            public HUF_CElt_s e161;
+            public HUF_CElt_s e162;
+            public HUF_CElt_s e163;
+            public HUF_CElt_s e164;
+            public HUF_CElt_s e165;
+            public HUF_CElt_s e166;
+            public HUF_CElt_s e167;
+            public HUF_CElt_s e168;
+            public HUF_CElt_s e169;
+            public HUF_CElt_s e170;
+            public HUF_CElt_s e171;
+            public HUF_CElt_s e172;
+            public HUF_CElt_s e173;
+            public HUF_CElt_s e174;
+            public HUF_CElt_s e175;
+            public HUF_CElt_s e176;
+            public HUF_CElt_s e177;
+            public HUF_CElt_s e178;
+            public HUF_CElt_s e179;
+            public HUF_CElt_s e180;
+            public HUF_CElt_s e181;
+            public HUF_CElt_s e182;
+            public HUF_CElt_s e183;
+            public HUF_CElt_s e184;
+            public HUF_CElt_s e185;
+            public HUF_CElt_s e186;
+            public HUF_CElt_s e187;
+            public HUF_CElt_s e188;
+            public HUF_CElt_s e189;
+            public HUF_CElt_s e190;
+            public HUF_CElt_s e191;
+            public HUF_CElt_s e192;
+            public HUF_CElt_s e193;
+            public HUF_CElt_s e194;
+            public HUF_CElt_s e195;
+            public HUF_CElt_s e196;
+            public HUF_CElt_s e197;
+            public HUF_CElt_s e198;
+            public HUF_CElt_s e199;
+            public HUF_CElt_s e200;
+            public HUF_CElt_s e201;
+            public HUF_CElt_s e202;
+            public HUF_CElt_s e203;
+            public HUF_CElt_s e204;
+            public HUF_CElt_s e205;
+            public HUF_CElt_s e206;
+            public HUF_CElt_s e207;
+            public HUF_CElt_s e208;
+            public HUF_CElt_s e209;
+            public HUF_CElt_s e210;
+            public HUF_CElt_s e211;
+            public HUF_CElt_s e212;
+            public HUF_CElt_s e213;
+            public HUF_CElt_s e214;
+            public HUF_CElt_s e215;
+            public HUF_CElt_s e216;
+            public HUF_CElt_s e217;
+            public HUF_CElt_s e218;
+            public HUF_CElt_s e219;
+            public HUF_CElt_s e220;
+            public HUF_CElt_s e221;
+            public HUF_CElt_s e222;
+            public HUF_CElt_s e223;
+            public HUF_CElt_s e224;
+            public HUF_CElt_s e225;
+            public HUF_CElt_s e226;
+            public HUF_CElt_s e227;
+            public HUF_CElt_s e228;
+            public HUF_CElt_s e229;
+            public HUF_CElt_s e230;
+            public HUF_CElt_s e231;
+            public HUF_CElt_s e232;
+            public HUF_CElt_s e233;
+            public HUF_CElt_s e234;
+            public HUF_CElt_s e235;
+            public HUF_CElt_s e236;
+            public HUF_CElt_s e237;
+            public HUF_CElt_s e238;
+            public HUF_CElt_s e239;
+            public HUF_CElt_s e240;
+            public HUF_CElt_s e241;
+            public HUF_CElt_s e242;
+            public HUF_CElt_s e243;
+            public HUF_CElt_s e244;
+            public HUF_CElt_s e245;
+            public HUF_CElt_s e246;
+            public HUF_CElt_s e247;
+            public HUF_CElt_s e248;
+            public HUF_CElt_s e249;
+            public HUF_CElt_s e250;
+            public HUF_CElt_s e251;
+            public HUF_CElt_s e252;
+            public HUF_CElt_s e253;
+            public HUF_CElt_s e254;
+            public HUF_CElt_s e255;
+
+            public ref HUF_CElt_s this[int index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + (uint)index);
+            }
+
+            public ref HUF_CElt_s this[uint index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + index);
+            }
+
+            public ref HUF_CElt_s this[nuint index]
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                [InlineMethod.Inline]
+                get => ref *(this + (uint)index);
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            [InlineMethod.Inline]
+            public static implicit operator HUF_CElt_s*(in _CTable_e__FixedBuffer t)
+            {
+                Ldarg_0();
+                Ldflda(new FieldRef(typeof(_CTable_e__FixedBuffer), nameof(e0)));
+                return IL.ReturnPointer<HUF_CElt_s>();
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            [InlineMethod.Inline]
+            public static HUF_CElt_s* operator +(in _CTable_e__FixedBuffer t, uint index)
+            {
+                Ldarg_0();
+                Ldflda(new FieldRef(typeof(_CTable_e__FixedBuffer), nameof(e0)));
+                Ldarg_1();
+                Conv_I();
+                Sizeof<HUF_CElt_s>();
+                Conv_I();
+                Mul();
+                Add();
+                return IL.ReturnPointer<HUF_CElt_s>();
+            }
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_decompress_usingDTable_t.cs

@@ -0,0 +1,8 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace ZstdSharp.Unsafe
+{
+    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+    public unsafe delegate nuint HUF_decompress_usingDTable_t(void* dst, nuint dstSize, void* cSrc, nuint cSrcSize, uint* DTable);
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_nbStreams_e.cs

@@ -0,0 +1,10 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public enum HUF_nbStreams_e
+    {
+        HUF_singleStream,
+        HUF_fourStreams,
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/HUF_repeat.cs

@@ -0,0 +1,11 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public enum HUF_repeat
+    {
+        HUF_repeat_none,
+        HUF_repeat_check,
+        HUF_repeat_valid,
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/Hist.cs

@@ -0,0 +1,240 @@
+using System;
+using static ZstdSharp.UnsafeHelper;
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        /* --- Error management --- */
+        public static uint HIST_isError(nuint code)
+        {
+            return ERR_isError(code);
+        }
+
+        /*-**************************************************************
+         *  Histogram functions
+         ****************************************************************/
+        public static uint HIST_count_simple(uint* count, uint* maxSymbolValuePtr, void* src, nuint srcSize)
+        {
+            byte* ip = (byte*)(src);
+            byte* end = ip + srcSize;
+            uint maxSymbolValue = *maxSymbolValuePtr;
+            uint largestCount = 0;
+
+            memset((void*)(count), (0), ((maxSymbolValue + 1) * (nuint)(sizeof(uint))));
+            if (srcSize == 0)
+            {
+                *maxSymbolValuePtr = 0;
+                return 0;
+            }
+
+            while (ip < end)
+            {
+                assert(*ip <= maxSymbolValue);
+                count[*ip++]++;
+            }
+
+            while ((count[maxSymbolValue]) == 0)
+            {
+                maxSymbolValue--;
+            }
+
+            *maxSymbolValuePtr = maxSymbolValue;
+
+            {
+                uint s;
+
+                for (s = 0; s <= maxSymbolValue; s++)
+                {
+                    if (count[s] > largestCount)
+                    {
+                        largestCount = count[s];
+                    }
+                }
+            }
+
+            return largestCount;
+        }
+
+        /* HIST_count_parallel_wksp() :
+         * store histogram into 4 intermediate tables, recombined at the end.
+         * this design makes better use of OoO cpus,
+         * and is noticeably faster when some values are heavily repeated.
+         * But it needs some additional workspace for intermediate tables.
+         * `workSpace` must be a U32 table of size >= HIST_WKSP_SIZE_U32.
+         * @return : largest histogram frequency,
+         *           or an error code (notably when histogram's alphabet is larger than *maxSymbolValuePtr) */
+        private static nuint HIST_count_parallel_wksp(uint* count, uint* maxSymbolValuePtr, void* source, nuint sourceSize, HIST_checkInput_e check, uint* workSpace)
+        {
+            byte* ip = (byte*)(source);
+            byte* iend = ip + sourceSize;
+            nuint countSize = (*maxSymbolValuePtr + 1) * (nuint)(4);
+            uint max = 0;
+            uint* Counting1 = workSpace;
+            uint* Counting2 = Counting1 + 256;
+            uint* Counting3 = Counting2 + 256;
+            uint* Counting4 = Counting3 + 256;
+
+            assert(*maxSymbolValuePtr <= 255);
+            if (sourceSize == 0)
+            {
+                memset((void*)(count), (0), (countSize));
+                *maxSymbolValuePtr = 0;
+                return 0;
+            }
+
+            memset((void*)(workSpace), (0), ((uint)(4 * 256) * (nuint)(sizeof(uint))));
+
+            {
+                uint cached = MEM_read32((void*)ip);
+
+                ip += 4;
+                while (ip < iend - 15)
+                {
+                    uint c = cached;
+
+                    cached = MEM_read32((void*)ip);
+                    ip += 4;
+                    Counting1[(byte)(c)]++;
+                    Counting2[(byte)(c >> 8)]++;
+                    Counting3[(byte)(c >> 16)]++;
+                    Counting4[c >> 24]++;
+                    c = cached;
+                    cached = MEM_read32((void*)ip);
+                    ip += 4;
+                    Counting1[(byte)(c)]++;
+                    Counting2[(byte)(c >> 8)]++;
+                    Counting3[(byte)(c >> 16)]++;
+                    Counting4[c >> 24]++;
+                    c = cached;
+                    cached = MEM_read32((void*)ip);
+                    ip += 4;
+                    Counting1[(byte)(c)]++;
+                    Counting2[(byte)(c >> 8)]++;
+                    Counting3[(byte)(c >> 16)]++;
+                    Counting4[c >> 24]++;
+                    c = cached;
+                    cached = MEM_read32((void*)ip);
+                    ip += 4;
+                    Counting1[(byte)(c)]++;
+                    Counting2[(byte)(c >> 8)]++;
+                    Counting3[(byte)(c >> 16)]++;
+                    Counting4[c >> 24]++;
+                }
+
+                ip -= 4;
+            }
+
+            while (ip < iend)
+            {
+                Counting1[*ip++]++;
+            }
+
+
+            {
+                uint s;
+
+                for (s = 0; s < 256; s++)
+                {
+                    Counting1[s] += Counting2[s] + Counting3[s] + Counting4[s];
+                    if (Counting1[s] > max)
+                    {
+                        max = Counting1[s];
+                    }
+                }
+            }
+
+
+            {
+                uint maxSymbolValue = 255;
+
+                while ((Counting1[maxSymbolValue]) == 0)
+                {
+                    maxSymbolValue--;
+                }
+
+                if (check != default && maxSymbolValue > *maxSymbolValuePtr)
+                {
+                    return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_maxSymbolValue_tooSmall)));
+                }
+
+                *maxSymbolValuePtr = maxSymbolValue;
+                memmove((void*)(count), (void*)(Counting1), (countSize));
+            }
+
+            return (nuint)(max);
+        }
+
+        /* HIST_countFast_wksp() :
+         * Same as HIST_countFast(), but using an externally provided scratch buffer.
+         * `workSpace` is a writable buffer which must be 4-bytes aligned,
+         * `workSpaceSize` must be >= HIST_WKSP_SIZE
+         */
+        public static nuint HIST_countFast_wksp(uint* count, uint* maxSymbolValuePtr, void* source, nuint sourceSize, void* workSpace, nuint workSpaceSize)
+        {
+            if (sourceSize < 1500)
+            {
+                return HIST_count_simple(count, maxSymbolValuePtr, source, sourceSize);
+            }
+
+            if (((nuint)(workSpace) & 3) != 0)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            }
+
+            if (workSpaceSize < (1024 * (nuint)(sizeof(uint))))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_workSpace_tooSmall)));
+            }
+
+            return HIST_count_parallel_wksp(count, maxSymbolValuePtr, source, sourceSize, HIST_checkInput_e.trustInput, (uint*)(workSpace));
+        }
+
+        /* HIST_count_wksp() :
+         * Same as HIST_count(), but using an externally provided scratch buffer.
+         * `workSpace` size must be table of >= HIST_WKSP_SIZE_U32 unsigned */
+        public static nuint HIST_count_wksp(uint* count, uint* maxSymbolValuePtr, void* source, nuint sourceSize, void* workSpace, nuint workSpaceSize)
+        {
+            if (((nuint)(workSpace) & 3) != 0)
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_GENERIC)));
+            }
+
+            if (workSpaceSize < (1024 * (nuint)(sizeof(uint))))
+            {
+                return (unchecked((nuint)(-(int)ZSTD_ErrorCode.ZSTD_error_workSpace_tooSmall)));
+            }
+
+            if (*maxSymbolValuePtr < 255)
+            {
+                return HIST_count_parallel_wksp(count, maxSymbolValuePtr, source, sourceSize, HIST_checkInput_e.checkMaxSymbolValue, (uint*)(workSpace));
+            }
+
+            *maxSymbolValuePtr = 255;
+            return HIST_countFast_wksp(count, maxSymbolValuePtr, source, sourceSize, workSpace, workSpaceSize);
+        }
+
+        /* fast variant (unsafe : won't check if src contains values beyond count[] limit) */
+        public static nuint HIST_countFast(uint* count, uint* maxSymbolValuePtr, void* source, nuint sourceSize)
+        {
+            uint* tmpCounters = stackalloc uint[1024];
+
+            return HIST_countFast_wksp(count, maxSymbolValuePtr, source, sourceSize, (void*)tmpCounters, (nuint)(sizeof(uint) * 1024));
+        }
+
+        /*! HIST_count():
+         *  Provides the precise count of each byte within a table 'count'.
+         * 'count' is a table of unsigned int, of minimum size (*maxSymbolValuePtr+1).
+         *  Updates *maxSymbolValuePtr with actual largest symbol value detected.
+         * @return : count of the most frequent symbol (which isn't identified).
+         *           or an error code, which can be tested using HIST_isError().
+         *           note : if return == srcSize, there is only one symbol.
+         */
+        public static nuint HIST_count(uint* count, uint* maxSymbolValuePtr, void* src, nuint srcSize)
+        {
+            uint* tmpCounters = stackalloc uint[1024];
+
+            return HIST_count_wksp(count, maxSymbolValuePtr, src, srcSize, (void*)tmpCounters, (nuint)(sizeof(uint) * 1024));
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/Mem.cs

@@ -0,0 +1,225 @@
+using System;
+using System.Buffers.Binary;
+using System.Runtime.CompilerServices;
+using InlineIL;
+using static InlineIL.IL.Emit;
+
+// ReSharper disable InconsistentNaming
+// ReSharper disable IdentifierTypo
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        /*-**************************************************************
+        *  Memory I/O API
+        *****************************************************************/
+        /*=== Static platform detection ===*/
+        public static bool MEM_32bits => sizeof(nint) == 4;
+
+        public static bool MEM_64bits => sizeof(nint) == 8;
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        /* default method, safe and standard.
+           can sometimes prove slower */
+        [InlineMethod.Inline]
+        private static ushort MEM_read16(void* memPtr)
+        {
+            Ldarg(nameof(memPtr));
+            Unaligned(1);
+            Ldind_U2();
+            return IL.Return<ushort>();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static uint MEM_read32(void* memPtr)
+        {
+            Ldarg(nameof(memPtr));
+            Unaligned(1);
+            Ldind_U4();
+            return IL.Return<uint>();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static ulong MEM_read64(void* memPtr)
+        {
+            Ldarg(nameof(memPtr));
+            Unaligned(1);
+            Ldind_I8();
+            return IL.Return<ulong>();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static nuint MEM_readST(void* memPtr)
+        {
+            Ldarg(nameof(memPtr));
+            Unaligned(1);
+            Ldind_I();
+            return IL.Return<nuint>();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static void MEM_write64(void* memPtr, ulong value)
+        {
+            Ldarg(nameof(memPtr));
+            Ldarg(nameof(value));
+            Unaligned(1);
+            Stind_I8();
+        }
+
+        /*=== Little endian r/w ===*/
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static ushort MEM_readLE16(void* memPtr)
+        {
+            Ldarg(nameof(memPtr));
+            Unaligned(1);
+            Ldind_U2();
+
+            if (!BitConverter.IsLittleEndian)
+            {
+                Call(new MethodRef(typeof(BinaryPrimitives), nameof(BinaryPrimitives.ReverseEndianness), typeof(ushort)));
+            }
+
+            return IL.Return<ushort>();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static void MEM_writeLE16(void* memPtr, ushort val)
+        {
+            Ldarg(nameof(memPtr));
+            Ldarg(nameof(val));
+
+            if (!BitConverter.IsLittleEndian)
+            {
+                Call(new MethodRef(typeof(BinaryPrimitives), nameof(BinaryPrimitives.ReverseEndianness),
+                    typeof(ushort)));
+            }
+
+            Unaligned(1);
+            Stind_I2();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static uint MEM_readLE24(void* memPtr) =>
+            (uint) (MEM_readLE16(memPtr) + (((byte*) memPtr)[2] << 16));
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static void MEM_writeLE24(void* memPtr, uint val)
+        {
+            MEM_writeLE16(memPtr, (ushort) val);
+            ((byte*) memPtr)[2] = (byte) (val >> 16);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static uint MEM_readLE32(void* memPtr)
+        {
+            Ldarg(nameof(memPtr));
+            Unaligned(1);
+            Ldind_U4();
+
+            if (!BitConverter.IsLittleEndian)
+            {
+                Call(new MethodRef(typeof(BinaryPrimitives), nameof(BinaryPrimitives.ReverseEndianness), typeof(uint)));
+            }
+
+            return IL.Return<uint>();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static void MEM_writeLE32(void* memPtr, uint val32)
+        {
+            Ldarg(nameof(memPtr));
+            Ldarg(nameof(val32));
+
+            if (!BitConverter.IsLittleEndian)
+            {
+                Call(new MethodRef(typeof(BinaryPrimitives), nameof(BinaryPrimitives.ReverseEndianness),
+                    typeof(uint)));
+            }
+
+            Unaligned(1);
+            Stind_I4();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static ulong MEM_readLE64(void* memPtr)
+        {
+            Ldarg(nameof(memPtr));
+            Unaligned(1);
+            Ldind_I8();
+
+            if (!BitConverter.IsLittleEndian)
+            {
+                Call(new MethodRef(typeof(BinaryPrimitives), nameof(BinaryPrimitives.ReverseEndianness), typeof(ulong)));
+            }
+
+            return IL.Return<ulong>();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static void MEM_writeLE64(void* memPtr, ulong val64)
+        {
+            Ldarg(nameof(memPtr));
+            Ldarg(nameof(val64));
+
+            if (!BitConverter.IsLittleEndian)
+            {
+                Call(new MethodRef(typeof(BinaryPrimitives), nameof(BinaryPrimitives.ReverseEndianness),
+                    typeof(ulong)));
+            }
+
+            Unaligned(1);
+            Stind_I8();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static nuint MEM_readLEST(void* memPtr)
+        {
+            Ldarg(nameof(memPtr));
+            Unaligned(1);
+            Ldind_I();
+
+            if (!BitConverter.IsLittleEndian)
+            {
+                Conv_U8();
+                Call(new MethodRef(typeof(BinaryPrimitives), nameof(BinaryPrimitives.ReverseEndianness),
+                    typeof(ulong)));
+                Conv_U();
+            }
+
+            return IL.Return<nuint>();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        [InlineMethod.Inline]
+        private static void MEM_writeLEST(void* memPtr, nuint val)
+        {
+            Ldarg(nameof(memPtr));
+            Ldarg(nameof(val));
+
+            if (!BitConverter.IsLittleEndian)
+            {
+                Conv_U8();
+                Call(new MethodRef(typeof(BinaryPrimitives), nameof(BinaryPrimitives.ReverseEndianness),
+                    typeof(ulong)));
+                Conv_U();
+            }
+
+            Unaligned(1);
+            Stind_I();
+        }
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/SeqCollector.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public unsafe partial struct SeqCollector
+    {
+        public int collectSequences;
+
+        public ZSTD_Sequence* seqStart;
+
+        public nuint seqIndex;
+
+        public nuint maxSequences;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/XXH32_canonical_t.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /* **************************
+    *  Canonical representation
+    ****************************/
+    /* Default result type for XXH functions are primitive unsigned 32 and 64 bits.
+    *  The canonical representation uses human-readable write convention, aka big-endian (large digits first).
+    *  These functions allow transformation of hash result into and from its canonical format.
+    *  This way, hash values can be written into a file / memory, and remain comparable on different systems and programs.
+    */
+    public unsafe partial struct XXH32_canonical_t
+    {
+        public fixed byte digest[4];
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/XXH32_state_s.cs

@@ -0,0 +1,30 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    /* These definitions are only meant to allow allocation of XXH state
+       statically, on stack, or in a struct for example.
+       Do not use members directly. */
+    public unsafe partial struct XXH32_state_s
+    {
+        public uint total_len_32;
+
+        public uint large_len;
+
+        public uint v1;
+
+        public uint v2;
+
+        public uint v3;
+
+        public uint v4;
+
+        /* buffer defined as U32 for alignment */
+        public fixed uint mem32[4];
+
+        public uint memsize;
+
+        /* never read nor write, will be removed in a future version */
+        public uint reserved;
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/XXH64_state_s.cs

@@ -0,0 +1,25 @@
+using System;
+
+namespace ZstdSharp.Unsafe
+{
+    public unsafe partial struct XXH64_state_s
+    {
+        public ulong total_len;
+
+        public ulong v1;
+
+        public ulong v2;
+
+        public ulong v3;
+
+        public ulong v4;
+
+        /* buffer defined as U64 for alignment */
+        public fixed ulong mem64[4];
+
+        public uint memsize;
+
+        /* never read nor write, will be removed in a future version */
+        public fixed uint reserved[2];
+    }
+}

src/SharpCompress/Compressors/Zstd/Unsafe/Xxhash.cs

@@ -0,0 +1,260 @@
+using System;
+using System.Buffers.Binary;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using static ZstdSharp.UnsafeHelper;
+// ReSharper disable InconsistentNaming
+// ReSharper disable IdentifierTypo
+
+namespace ZstdSharp.Unsafe
+{
+    public static unsafe partial class Methods
+    {
+        private static void XXH_memcpy(void* dest, void* src, ulong size)
+        {
+            memcpy((dest), (src), (size));
+        }
+        
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static uint XXH_readLE32(void* ptr) => 
+            BitConverter.IsLittleEndian ? *(uint*) ptr : BinaryPrimitives.ReverseEndianness(*(uint*) ptr);
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static ulong XXH_readLE64(void* ptr) => 
+            BitConverter.IsLittleEndian ? *(ulong*) ptr : BinaryPrimitives.ReverseEndianness(*(ulong*) ptr);
+
+        public const ulong PRIME64_1 = 11400714785074694791UL;
+
+        public const ulong PRIME64_2 = 14029467366897019727UL;
+
+        public const ulong PRIME64_3 = 1609587929392839161UL;
+
+        public const ulong PRIME64_4 = 9650029242287828579UL;
+
+        public const ulong PRIME64_5 = 2870177450012600261UL;
+
+        public static uint XXH_versionNumber()
+        {
+            return 0 * 100 * 100 + 6 * 100 + 2;
+        }
+
+        private static ulong XXH64_round(ulong acc, ulong input)
+        {
+            acc += input * PRIME64_2;
+            acc = BitOperations.RotateLeft(acc, 31);
+            acc *= PRIME64_1;
+            return acc;
+        }
+
+        private static ulong XXH64_mergeRound(ulong acc, ulong val)
+        {
+            val = XXH64_round(0, val);
+            acc ^= val;
+            acc = acc * PRIME64_1 + PRIME64_4;
+            return acc;
+        }
+
+        public static void XXH64_reset(XXH64_state_s* statePtr, ulong seed)
+        {
+            XXH64_state_s state;
+
+            memset(&state, (0), ((ulong)((sizeof(XXH64_state_s) - 8))));
+            state.v1 = seed + PRIME64_1 + PRIME64_2;
+            state.v2 = seed + PRIME64_2;
+            state.v3 = seed + 0;
+            state.v4 = seed - PRIME64_1;
+            memcpy(statePtr, &state, ((ulong)sizeof(XXH64_state_s)));
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void XXH64_update(XXH64_state_s* state, void* input, ulong len)
+        {
+            byte* p = (byte*)(input);
+            byte* bEnd = p + len;
+
+            state->total_len += len;
+            if (state->memsize + len < 32)
+            {
+                if (input != null)
+                {
+                    XXH_memcpy(((byte*)(state->mem64)) + state->memsize, input, len);
+                }
+
+                state->memsize += (uint)(len);
+                return;
+            }
+
+            if (state->memsize != 0)
+            {
+                XXH_memcpy(((byte*)(state->mem64)) + state->memsize, input, 32 - state->memsize);
+                state->v1 = XXH64_round(state->v1, XXH_readLE64(state->mem64 + 0));
+                state->v2 = XXH64_round(state->v2, XXH_readLE64(state->mem64 + 1));
+                state->v3 = XXH64_round(state->v3, XXH_readLE64(state->mem64 + 2));
+                state->v4 = XXH64_round(state->v4, XXH_readLE64(state->mem64 + 3));
+                p += 32 - state->memsize;
+                state->memsize = 0;
+            }
+
+            if (p + 32 <= bEnd)
+            {
+                byte* limit = bEnd - 32;
+                ulong v1 = state->v1;
+                ulong v2 = state->v2;
+                ulong v3 = state->v3;
+                ulong v4 = state->v4;
+
+                do
+                {
+                    v1 = XXH64_round(v1, XXH_readLE64(p));
+                    p += 8;
+                    v2 = XXH64_round(v2, XXH_readLE64(p));
+                    p += 8;
+                    v3 = XXH64_round(v3, XXH_readLE64(p));
+                    p += 8;
+                    v4 = XXH64_round(v4, XXH_readLE64(p));
+                    p += 8;
+                }
+                while (p <= limit);
+
+                state->v1 = v1;
+                state->v2 = v2;
+                state->v3 = v3;
+                state->v4 = v4;
+            }
+
+            if (p < bEnd)
+            {
+                XXH_memcpy(state->mem64, p, (ulong)(bEnd - p));
+                state->memsize = (uint)(bEnd - p);
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static ulong XXH64_digest(XXH64_state_s* state)
+        {
+            byte* p = (byte*)(state->mem64);
+            byte* bEnd = (byte*)(state->mem64) + state->memsize;
+            ulong h64;
+
+            if (state->total_len >= 32)
+            {
+                ulong v1 = state->v1;
+                ulong v2 = state->v2;
+                ulong v3 = state->v3;
+                ulong v4 = state->v4;
+
+                h64 = BitOperations.RotateLeft(v1, 1) + BitOperations.RotateLeft(v2, 7) + BitOperations.RotateLeft(v3, 12) + BitOperations.RotateLeft(v4, 18);
+                h64 = XXH64_mergeRound(h64, v1);
+                h64 = XXH64_mergeRound(h64, v2);
+                h64 = XXH64_mergeRound(h64, v3);
+                h64 = XXH64_mergeRound(h64, v4);
+            }
+            else
+            {
+                h64 = state->v3 + PRIME64_5;
+            }
+
+            h64 += state->total_len;
+            while (p + 8 <= bEnd)
+            {
+                ulong k1 = XXH64_round(0, XXH_readLE64(p));
+
+                h64 ^= k1;
+                h64 = BitOperations.RotateLeft(h64, 27) * PRIME64_1 + PRIME64_4;
+                p += 8;
+            }
+
+            if (p + 4 <= bEnd)
+            {
+                h64 ^= XXH_readLE32(p) * PRIME64_1;
+                h64 = BitOperations.RotateLeft(h64, 23) * PRIME64_2 + PRIME64_3;
+                p += 4;
+            }
+
+            while (p < bEnd)
+            {
+                h64 ^= *p * PRIME64_5;
+                h64 = BitOperations.RotateLeft(h64, 11) * PRIME64_1;
+                p++;
+            }
+
+            h64 ^= h64>>33;
+            h64 *= PRIME64_2;
+            h64 ^= h64>>29;
+            h64 *= PRIME64_3;
+            h64 ^= h64>>32;
+            return h64;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static ulong XXH64(void* input, ulong len, ulong seed)
+        {
+            byte* p = (byte*)(input);
+            byte* bEnd = p + len;
+            ulong h64;
+
+            if (len >= ((ulong)(32)))
+            {
+                byte* limit = bEnd - 32;
+                ulong v1 = seed + PRIME64_1 + PRIME64_2;
+                ulong v2 = seed + PRIME64_2;
+                ulong v3 = seed + ((ulong)(0));
+                ulong v4 = seed - PRIME64_1;
+
+                do
+                {
+                    v1 = XXH64_round(v1, XXH_readLE64(((void*)(p))));
+                    p += 8;
+                    v2 = XXH64_round(v2, XXH_readLE64(((void*)(p))));
+                    p += 8;
+                    v3 = XXH64_round(v3, XXH_readLE64(((void*)(p))));
+                    p += 8;
+                    v4 = XXH64_round(v4, XXH_readLE64(((void*)(p))));
+                    p += 8;
+                }
+                while (p <= limit);
+
+                h64 = BitOperations.RotateLeft(v1, 1) + BitOperations.RotateLeft(v2, 7) + BitOperations.RotateLeft(v3, 12) + BitOperations.RotateLeft(v4, 18);
+                h64 = XXH64_mergeRound(h64, v1);
+                h64 = XXH64_mergeRound(h64, v2);
+                h64 = XXH64_mergeRound(h64, v3);
+                h64 = XXH64_mergeRound(h64, v4);
+            }
+            else
+            {
+                h64 = seed + PRIME64_5;
+            }
+
+            h64 += (ulong)(len);
+            while (p + 8 <= bEnd)
+            {
+                ulong k1 = XXH64_round(((ulong)(0)), XXH_readLE64(((void*)(p))));
+
+                h64 ^= k1;
+                h64 = BitOperations.RotateLeft(h64, 27) * PRIME64_1 + PRIME64_4;
+                p += 8;
+            }
+
+            if (p + 4 <= bEnd)
+            {
+                h64 ^= (ulong)(XXH_readLE32(((void*)(p)))) * PRIME64_1;
+                h64 = BitOperations.RotateLeft(h64, 23) * PRIME64_2 + PRIME64_3;
+                p += 4;
+            }
+
+            while (p < bEnd)
+            {
+                h64 ^= ((ulong)((*p))) * PRIME64_5;
+                h64 = BitOperations.RotateLeft(h64, 11) * PRIME64_1;
+                p++;
+            }
+
+            h64 ^= h64 >> 33;
+            h64 *= PRIME64_2;
+            h64 ^= h64 >> 29;
+            h64 *= PRIME64_3;
+            h64 ^= h64 >> 32;
+            return h64;
+        }
+    }
+}