Add PpmdStream class for PPMd decompression support

Aaru.Compression/Aaru.Compression.csproj

@@ -78,6 +78,7 @@
     <Compile Include="XZ.cs"/>
     <Compile Include="Zip\Deflate64Stream.cs" />
     <Compile Include="Zip\ImplodeStream.cs"/>
+    <Compile Include="Zip\PpmdStream.cs" />
     <Compile Include="Zip\ReduceStream.cs"/>
     <Compile Include="Zip\ShrinkStream.cs"/>
     <Compile Include="ZSTD.cs"/>

Aaru.Compression/Zip/PpmdStream.cs

@@ -0,0 +1,118 @@
+using System;
+using System.IO;
+using System.Runtime.InteropServices;
+
+// ReSharper disable LocalizableElement
+
+namespace Aaru.Compression.Zip;
+
+public partial class PpmdStream : Stream
+{
+    readonly byte[] _decoded;
+    readonly long   _length;
+    long            _position;
+
+    public PpmdStream(Stream compressedStream, long decompressedLength, int maxOrder, int subAllocSize, bool restoration)
+    {
+        if(compressedStream == null) throw new ArgumentNullException(nameof(compressedStream));
+        if(!compressedStream.CanRead) throw new ArgumentException("Stream must be readable", nameof(compressedStream));
+        if(decompressedLength < 0) throw new ArgumentOutOfRangeException(nameof(decompressedLength));
+
+        // Read full compressed data into memory
+        compressedStream.Position = 0;
+        var inBuf = new byte[compressedStream.Length];
+        compressedStream.ReadExactly(inBuf, 0, inBuf.Length);
+
+        // Allocate output buffer
+        _decoded = new byte[decompressedLength];
+        var outLen = (nint)decompressedLength;
+
+        // Call native decompressor
+        int err = AARU_zip_ppmd_decode_buffer(_decoded,
+                                              ref outLen,
+                                              inBuf,
+                                              inBuf.Length,
+                                              maxOrder,
+                                              subAllocSize,
+                                              restoration ? 1 : 0);
+
+        if(err != 0) throw new InvalidOperationException("PPMd decompression failed");
+
+        // Adjust actual length in case it differs
+        _length   = outLen;
+        _position = 0;
+    }
+
+    public override bool CanRead  => true;
+    public override bool CanSeek  => true;
+    public override bool CanWrite => false;
+    public override long Length   => _length;
+
+    public override long Position
+    {
+        get => _position;
+        set => Seek(value, SeekOrigin.Begin);
+    }
+
+    [LibraryImport("libAaru.Compression.Native")]
+    public static partial int AARU_zip_ppmd_decode_buffer(byte[] dst_buffer, ref nint dst_size,  byte[] src_buffer,
+                                                          nint   src_size,   int      max_order, int    sub_alloc_size,
+                                                          int    restoration);
+
+    public override void Flush()
+    {
+        // no-op
+    }
+
+    /// <summary>
+    ///     Reads up to <paramref name="count" /> bytes from the decompressed buffer
+    ///     into <paramref name="buffer" />, starting at <paramref name="offset" />.
+    /// </summary>
+    public override int Read(byte[] buffer, int offset, int count)
+    {
+        if(buffer         == null) throw new ArgumentNullException(nameof(buffer));
+        if(offset         < 0) throw new ArgumentOutOfRangeException(nameof(offset));
+        if(count          < 0) throw new ArgumentOutOfRangeException(nameof(count));
+        if(offset + count > buffer.Length) throw new ArgumentException("offset+count exceeds buffer length");
+
+        long remaining = _length - _position;
+
+        if(remaining <= 0) return 0;
+
+        var toRead = (int)Math.Min(count, remaining);
+        Array.Copy(_decoded, _position, buffer, offset, toRead);
+        _position += toRead;
+
+        return toRead;
+    }
+
+    /// <summary>
+    ///     Sets the current position within the decompressed buffer.
+    /// </summary>
+    public override long Seek(long offset, SeekOrigin origin)
+    {
+        long newPos = origin switch
+                      {
+                          SeekOrigin.Begin   => offset,
+                          SeekOrigin.Current => _position + offset,
+                          SeekOrigin.End     => _length   + offset,
+                          _                  => throw new ArgumentException("Invalid SeekOrigin", nameof(origin))
+                      };
+
+        if(newPos < 0 || newPos > _length) throw new IOException("Attempt to seek outside the buffer");
+
+        _position = newPos;
+
+        return _position;
+    }
+
+    public override void SetLength(long value)
+    {
+        throw new NotSupportedException("Cannot resize decompressed buffer");
+    }
+
+    public override void Write(byte[] buffer, int offset, int count)
+    {
+        throw new NotSupportedException("Stream is read-only");
+    }
+}