Arj's methods CompressedMost (1), Compressed (2) and CompressedFaster (3) implemented.

src/SharpCompress/Common/Arj/ArjFilePart.cs

@@ -38,6 +38,11 @@ namespace SharpCompress.Common.Arj
                             Header.CompressedSize
                         );
                         break;
+                    case CompressionMethod.CompressedMost:
+                    case CompressionMethod.Compressed:
+                    case CompressionMethod.CompressedFaster:
+                        compressedStream = new LhaStream<Lh7DecoderCfg>(_stream, (int)Header.OriginalSize);
+                        break;
                     case CompressionMethod.CompressedFastest:
                         compressedStream = new LHDecoderStream(_stream, (int)Header.OriginalSize);
                         break;

src/SharpCompress/Compressors/Arj/BitReader.cs

@@ -4,56 +4,68 @@ using System.IO;
 namespace SharpCompress.Compressors.Arj
 {
     [CLSCompliant(true)]
-    public sealed class BitReader
+    public class BitReader
     {
-        private readonly Stream _stream;
-        private int _bitBuffer;
-        private int _bitsRemaining;
-        private bool _disposed;
+        private readonly Stream _input;
+        private int _bitBuffer; // currently buffered bits
+        private int _bitCount; // number of bits in buffer
 
         public BitReader(Stream input)
         {
-            _stream = input ?? throw new ArgumentNullException(nameof(input));
-            if (!input.CanRead)
-                throw new ArgumentException("Stream must be readable.", nameof(input));
+            _input = input ?? throw new ArgumentNullException(nameof(input));
+            _bitBuffer = 0;
+            _bitCount = 0;
         }
 
+        /// <summary>
+        /// Reads a single bit from the stream. Returns 0 or 1.
+        /// </summary>
+        public int ReadBit()
+        {
+            if (_bitCount == 0)
+            {
+                int nextByte = _input.ReadByte();
+                if (nextByte < 0)
+                {
+                    throw new EndOfStreamException("No more data available in BitReader.");
+                }
+
+                _bitBuffer = nextByte;
+                _bitCount = 8;
+            }
+
+            int bit = (_bitBuffer >> (_bitCount - 1)) & 1;
+            _bitCount--;
+            return bit;
+        }
+
+        /// <summary>
+        /// Reads n bits (up to 32) from the stream.
+        /// </summary>
         public int ReadBits(int count)
         {
-            if (_disposed)
-                throw new ObjectDisposedException(nameof(BitReader));
-
-            if (count <= 0 || count > 32)
+            if (count < 0 || count > 32)
+            {
                 throw new ArgumentOutOfRangeException(
                     nameof(count),
-                    "Bit count must be between 1 and 32."
+                    "Count must be between 0 and 32."
                 );
+            }
 
             int result = 0;
             for (int i = 0; i < count; i++)
             {
-                if (_bitsRemaining == 0)
-                {
-                    int nextByte = _stream.ReadByte();
-                    if (nextByte == -1)
-                        throw new EndOfStreamException();
-
-                    _bitBuffer = nextByte;
-                    _bitsRemaining = 8;
-                }
-
-                // hoogste bit eerst
-                result = (result << 1) | ((_bitBuffer >> 7) & 1);
-                _bitBuffer <<= 1;
-                _bitsRemaining--;
+                result = (result << 1) | ReadBit();
             }
-
             return result;
         }
 
+        /// <summary>
+        /// Resets any buffered bits.
+        /// </summary>
         public void AlignToByte()
         {
-            _bitsRemaining = 0;
+            _bitCount = 0;
             _bitBuffer = 0;
         }
     }

src/SharpCompress/Compressors/Arj/HistoryIterator.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace SharpCompress.Compressors.Arj
+{
+    /// <summary>
+    /// Iterator that reads & pushes values back into the ring buffer.
+    /// </summary>
+    public class HistoryIterator : IEnumerator<byte>
+    {
+        private int _index;
+        private readonly IRingBuffer _ring;
+
+        public HistoryIterator(IRingBuffer ring, int startIndex)
+        {
+            _ring = ring;
+            _index = startIndex;
+        }
+
+        public bool MoveNext()
+        {
+            Current = _ring[_index];
+            _index = unchecked(_index + 1);
+
+            // Push value back into the ring buffer
+            _ring.Push(Current);
+
+            return true; // iterator is infinite
+        }
+
+        public void Reset()
+        {
+            throw new NotSupportedException();
+        }
+
+        public byte Current { get; private set; }
+
+        object IEnumerator.Current => Current;
+
+        public void Dispose() { }
+    }
+}

src/SharpCompress/Compressors/Arj/HuffmanTree.cs

@@ -0,0 +1,218 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+
+namespace SharpCompress.Compressors.Arj
+{
+    [CLSCompliant(true)]
+    public enum NodeType
+    {
+        Leaf,
+        Branch,
+    }
+
+    [CLSCompliant(true)]
+    public sealed class TreeEntry
+    {
+        public readonly NodeType Type;
+        public readonly int LeafValue;
+        public readonly int BranchIndex;
+
+        public const int MAX_INDEX = 4096;
+
+        private TreeEntry(NodeType type, int leafValue, int branchIndex)
+        {
+            Type = type;
+            LeafValue = leafValue;
+            BranchIndex = branchIndex;
+        }
+
+        public static TreeEntry Leaf(int value)
+        {
+            return new TreeEntry(NodeType.Leaf, value, -1);
+        }
+
+        public static TreeEntry Branch(int index)
+        {
+            if (index >= MAX_INDEX)
+            {
+                throw new ArgumentOutOfRangeException(
+                    nameof(index),
+                    "Branch index exceeds MAX_INDEX"
+                );
+            }
+            return new TreeEntry(NodeType.Branch, 0, index);
+        }
+    }
+
+    [CLSCompliant(true)]
+    public sealed class HuffTree
+    {
+        private readonly List<TreeEntry> _tree;
+
+        public HuffTree(int capacity = 0)
+        {
+            _tree = new List<TreeEntry>(capacity);
+        }
+
+        public void SetSingle(int value)
+        {
+            _tree.Clear();
+            _tree.Add(TreeEntry.Leaf(value));
+        }
+
+        public void BuildTree(byte[] lengths, int count)
+        {
+            if (lengths == null)
+            {
+                throw new ArgumentNullException(nameof(lengths));
+            }
+
+            if (count < 0 || count > lengths.Length)
+            {
+                throw new ArgumentOutOfRangeException(nameof(count));
+            }
+
+            if (count > TreeEntry.MAX_INDEX / 2)
+            {
+                throw new ArgumentException(
+                    $"Count exceeds maximum allowed: {TreeEntry.MAX_INDEX / 2}"
+                );
+            }
+            byte[] slice = new byte[count];
+            Array.Copy(lengths, slice, count);
+
+            BuildTree(slice);
+        }
+
+        public void BuildTree(byte[] valueLengths)
+        {
+            if (valueLengths == null)
+            {
+                throw new ArgumentNullException(nameof(valueLengths));
+            }
+
+            if (valueLengths.Length > TreeEntry.MAX_INDEX / 2)
+            {
+                throw new InvalidOperationException("Too many code lengths");
+            }
+
+            _tree.Clear();
+
+            int maxAllocated = 1; // start with a single (root) node
+
+            for (byte currentLen = 1; ; currentLen++)
+            {
+                // add missing branches up to current limit
+                int maxLimit = maxAllocated;
+
+                for (int i = _tree.Count; i < maxLimit; i++)
+                {
+                    // TreeEntry.Branch may throw if index too large
+                    try
+                    {
+                        _tree.Add(TreeEntry.Branch(maxAllocated));
+                    }
+                    catch (ArgumentOutOfRangeException e)
+                    {
+                        _tree.Clear();
+                        throw new InvalidOperationException("Branch index exceeds limit", e);
+                    }
+
+                    // each branch node allocates two children
+                    maxAllocated += 2;
+                }
+
+                // fill tree with leaves found in the lengths table at the current length
+                bool moreLeaves = false;
+
+                for (int value = 0; value < valueLengths.Length; value++)
+                {
+                    byte len = valueLengths[value];
+                    if (len == currentLen)
+                    {
+                        _tree.Add(TreeEntry.Leaf(value));
+                    }
+                    else if (len > currentLen)
+                    {
+                        moreLeaves = true; // there are more leaves to process
+                    }
+                }
+
+                // sanity check (too many leaves)
+                if (_tree.Count > maxAllocated)
+                {
+                    throw new InvalidOperationException("Too many leaves");
+                }
+
+                // stop when no longer finding longer codes
+                if (!moreLeaves)
+                {
+                    break;
+                }
+            }
+
+            // ensure tree is complete
+            if (_tree.Count != maxAllocated)
+            {
+                throw new InvalidOperationException(
+                    $"Missing some leaves: tree count = {_tree.Count}, expected = {maxAllocated}"
+                );
+            }
+        }
+
+        public int ReadEntry(BitReader reader)
+        {
+            if (_tree.Count == 0)
+            {
+                throw new InvalidOperationException("Tree not initialized");
+            }
+
+            TreeEntry node = _tree[0];
+            while (true)
+            {
+                if (node.Type == NodeType.Leaf)
+                {
+                    return node.LeafValue;
+                }
+
+                int bit = reader.ReadBit();
+                int index = node.BranchIndex + bit;
+
+                if (index >= _tree.Count)
+                {
+                    throw new InvalidOperationException("Invalid branch index during read");
+                }
+
+                node = _tree[index];
+            }
+        }
+
+        public override string ToString()
+        {
+            var result = new StringBuilder();
+
+            void FormatStep(int index, string prefix)
+            {
+                var node = _tree[index];
+                if (node.Type == NodeType.Leaf)
+                {
+                    result.AppendLine($"{prefix} -> {node.LeafValue}");
+                }
+                else
+                {
+                    FormatStep(node.BranchIndex, prefix + "0");
+                    FormatStep(node.BranchIndex + 1, prefix + "1");
+                }
+            }
+
+            if (_tree.Count > 0)
+            {
+                FormatStep(0, "");
+            }
+
+            return result.ToString();
+        }
+    }
+}

src/SharpCompress/Compressors/Arj/ILhaDecoderConfig.cs

@@ -0,0 +1,9 @@
+namespace SharpCompress.Compressors.Arj
+{
+    public interface ILhaDecoderConfig
+    {
+        int HistoryBits { get; }
+        int OffsetBits { get; }
+        RingBuffer RingBuffer { get; }
+    }
+}

src/SharpCompress/Compressors/Arj/IRingBuffer.cs

@@ -0,0 +1,17 @@
+namespace SharpCompress.Compressors.Arj
+{
+    public interface IRingBuffer
+    {
+        int BufferSize { get; }
+
+        int Cursor { get; }
+        void SetCursor(int pos);
+
+        void Push(byte value);
+
+        HistoryIterator IterFromOffset(int offset);
+        HistoryIterator IterFromPos(int pos);
+
+        byte this[int index] { get; }
+    }
+}

src/SharpCompress/Compressors/Arj/Lh5DecoderCfg.cs

@@ -0,0 +1,9 @@
+namespace SharpCompress.Compressors.Arj
+{
+    public class Lh5DecoderCfg : ILhaDecoderConfig
+    {
+        public int HistoryBits => 14;
+        public int OffsetBits => 4;
+        public RingBuffer RingBuffer { get; } = new RingBuffer(1 << 14);
+    }
+}

src/SharpCompress/Compressors/Arj/Lh7DecoderCfg.cs

@@ -0,0 +1,9 @@
+namespace SharpCompress.Compressors.Arj
+{
+    public class Lh7DecoderCfg : ILhaDecoderConfig
+    {
+        public int HistoryBits => 17;
+        public int OffsetBits => 5;
+        public RingBuffer RingBuffer { get; } = new RingBuffer(1 << 17);
+    }
+}

src/SharpCompress/Compressors/Arj/LhaStream.cs

@@ -0,0 +1,359 @@
+using System;
+using System.Data;
+using System.IO;
+using System.Linq;
+using SharpCompress.IO;
+
+namespace SharpCompress.Compressors.Arj
+{
+    [CLSCompliant(true)]
+    public sealed class LhaStream<C> : Stream, IStreamStack
+        where C : ILhaDecoderConfig, new()
+    {
+        private readonly BitReader _bitReader;
+        private readonly Stream _stream;
+
+        private readonly HuffTree _commandTree;
+        private readonly HuffTree _offsetTree;
+        private int _remainingCommands;
+        private (int offset, int count)? _copyProgress;
+        private readonly RingBuffer _ringBuffer;
+        private readonly C _config = new C();
+
+        private const int NUM_COMMANDS = 510;
+        private const int NUM_TEMP_CODELEN = 20;
+
+        private readonly int _originalSize;
+        private int _producedBytes = 0;
+
+#if DEBUG_STREAMS
+        long IStreamStack.InstanceId { get; set; }
+#endif
+        int IStreamStack.DefaultBufferSize { get; set; }
+
+        Stream IStreamStack.BaseStream() => _stream;
+
+        int IStreamStack.BufferSize
+        {
+            get => 0;
+            set { }
+        }
+        int IStreamStack.BufferPosition
+        {
+            get => 0;
+            set { }
+        }
+
+        void IStreamStack.SetPosition(long position) { }
+
+        public LhaStream(Stream compressedStream, int originalSize)
+        {
+            _stream = compressedStream ?? throw new ArgumentNullException(nameof(compressedStream));
+            _bitReader = new BitReader(compressedStream);
+            _ringBuffer = _config.RingBuffer;
+            _commandTree = new HuffTree(NUM_COMMANDS * 2);
+            _offsetTree = new HuffTree(NUM_TEMP_CODELEN * 2);
+            _remainingCommands = 0;
+            _copyProgress = null;
+            _originalSize = originalSize;
+        }
+
+        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() { }
+
+        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();
+
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            if (buffer == null)
+            {
+                throw new ArgumentNullException(nameof(buffer));
+            }
+            if (offset < 0 || count < 0 || (offset + count) > buffer.Length)
+            {
+                throw new ArgumentOutOfRangeException();
+            }
+
+            if (_producedBytes >= _originalSize)
+            {
+                return 0; // EOF
+            }
+            if (count == 0)
+            {
+                return 0;
+            }
+
+            byte[] temp = new byte[count];
+            FillBuffer(temp);
+
+            Array.Copy(temp, 0, buffer, offset, temp.Length);
+            return _producedBytes;
+        }
+
+        private byte ReadCodeLength()
+        {
+            byte len = (byte)_bitReader.ReadBits(3);
+            if (len == 7)
+            {
+                while (_bitReader.ReadBit() != 0)
+                {
+                    len++;
+                    if (len > 255)
+                    {
+                        throw new InvalidOperationException("Code length overflow");
+                    }
+                }
+            }
+            return len;
+        }
+
+        private int ReadCodeSkip(int skipRange)
+        {
+            int bits;
+            int increment;
+
+            switch (skipRange)
+            {
+                case 0:
+                    return 1;
+                case 1:
+                    bits = 4;
+                    increment = 3; // 3..=18
+                    break;
+                default:
+                    bits = 9;
+                    increment = 20; // 20..=531
+                    break;
+            }
+
+            int skip = _bitReader.ReadBits(bits);
+            return skip + increment;
+        }
+
+        private void ReadTempTree()
+        {
+            byte[] codeLengths = new byte[NUM_TEMP_CODELEN];
+
+            // number of codes to read (5 bits)
+            int numCodes = _bitReader.ReadBits(5);
+
+            // single code only
+            if (numCodes == 0)
+            {
+                int code = _bitReader.ReadBits(5);
+                _offsetTree.SetSingle((byte)code);
+                return;
+            }
+
+            if (numCodes > NUM_TEMP_CODELEN)
+            {
+                throw new Exception("temporary codelen table has invalid size");
+            }
+
+            // read actual lengths
+            int count = Math.Min(3, numCodes);
+            for (int i = 0; i < count; i++)
+            {
+                codeLengths[i] = (byte)ReadCodeLength();
+            }
+
+            // 2-bit skip value follows
+            int skip = _bitReader.ReadBits(2);
+
+            if (3 + skip > numCodes)
+            {
+                throw new Exception("temporary codelen table has invalid size");
+            }
+
+            for (int i = 3 + skip; i < numCodes; i++)
+            {
+                codeLengths[i] = (byte)ReadCodeLength();
+            }
+
+            _offsetTree.BuildTree(codeLengths, numCodes);
+        }
+
+        private void ReadCommandTree()
+        {
+            byte[] codeLengths = new byte[NUM_COMMANDS];
+
+            // number of codes to read (9 bits)
+            int numCodes = _bitReader.ReadBits(9);
+
+            // single code only
+            if (numCodes == 0)
+            {
+                int code = _bitReader.ReadBits(9);
+                _commandTree.SetSingle((ushort)code);
+                return;
+            }
+
+            if (numCodes > NUM_COMMANDS)
+            {
+                throw new Exception("commands codelen table has invalid size");
+            }
+
+            int index = 0;
+            while (index < numCodes)
+            {
+                for (int n = 0; n < numCodes - index; n++)
+                {
+                    int code = _offsetTree.ReadEntry(_bitReader);
+
+                    if (code >= 0 && code <= 2) // skip range
+                    {
+                        int skipCount = ReadCodeSkip(code);
+                        index += n + skipCount;
+                        goto outerLoop;
+                    }
+                    else
+                    {
+                        codeLengths[index + n] = (byte)(code - 2);
+                    }
+                }
+                break;
+
+                outerLoop:
+                ;
+            }
+
+            _commandTree.BuildTree(codeLengths, numCodes);
+        }
+
+        private void ReadOffsetTree()
+        {
+            int numCodes = _bitReader.ReadBits(_config.OffsetBits);
+            if (numCodes == 0)
+            {
+                int code = _bitReader.ReadBits(_config.OffsetBits);
+                _offsetTree.SetSingle(code);
+                return;
+            }
+
+            if (numCodes > _config.HistoryBits)
+            {
+                throw new InvalidDataException("Offset code table too large");
+            }
+
+            byte[] codeLengths = new byte[NUM_TEMP_CODELEN];
+            for (int i = 0; i < numCodes; i++)
+            {
+                codeLengths[i] = (byte)ReadCodeLength();
+            }
+
+            _offsetTree.BuildTree(codeLengths, numCodes);
+        }
+
+        private void BeginNewBlock()
+        {
+            _remainingCommands = _bitReader.ReadBits(16);
+            ReadTempTree();
+            ReadCommandTree();
+            ReadOffsetTree();
+        }
+
+        private int ReadCommand() => _commandTree.ReadEntry(_bitReader);
+
+        private int ReadOffset()
+        {
+            int bits = _offsetTree.ReadEntry(_bitReader);
+            if (bits <= 1)
+            {
+                return bits;
+            }
+
+            int res = _bitReader.ReadBits(bits - 1);
+            return res | (1 << (bits - 1));
+        }
+
+        private int CopyFromHistory(byte[] target, int targetIndex, int offset, int count)
+        {
+            var historyIter = _ringBuffer.IterFromOffset(offset);
+            int copied = 0;
+
+            while (
+                copied < count && historyIter.MoveNext() && (targetIndex + copied) < target.Length
+            )
+            {
+                target[targetIndex + copied] = historyIter.Current;
+                copied++;
+            }
+
+            if (copied < count)
+            {
+                _copyProgress = (offset, count - copied);
+            }
+
+            return copied;
+        }
+
+        public void FillBuffer(byte[] buffer)
+        {
+            int bufLen = buffer.Length;
+            int bufIndex = 0;
+
+            // stop when we reached original size
+            if (_producedBytes >= _originalSize)
+                return;
+
+            // calculate limit, so that we don't go over the original size
+            int remaining = (int)Math.Min(bufLen, _originalSize - _producedBytes);
+
+            while (bufIndex < remaining)
+            {
+                if (_copyProgress.HasValue)
+                {
+                    var (offset, count) = _copyProgress.Value;
+                    int copied = CopyFromHistory(
+                        buffer,
+                        bufIndex,
+                        offset,
+                        (int)Math.Min(count, remaining - bufIndex)
+                    );
+                    bufIndex += copied;
+                    _copyProgress = null;
+                }
+
+                if (_remainingCommands == 0)
+                {
+                    BeginNewBlock();
+                }
+
+                _remainingCommands--;
+
+                int command = ReadCommand();
+
+                if (command >= 0 && command <= 0xFF)
+                {
+                    byte value = (byte)command;
+                    buffer[bufIndex++] = value;
+                    _ringBuffer.Push(value);
+                }
+                else
+                {
+                    int count = command - 0x100 + 3;
+                    int offset = ReadOffset();
+                    int copyCount = (int)Math.Min(count, remaining - bufIndex);
+                    bufIndex += CopyFromHistory(buffer, bufIndex, offset, copyCount);
+                }
+            }
+
+            _producedBytes += bufIndex;
+        }
+    }
+}

src/SharpCompress/Compressors/Arj/RingBuffer.cs

@@ -0,0 +1,67 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace SharpCompress.Compressors.Arj
+{
+    /// <summary>
+    /// A fixed-size ring buffer where N must be a power of two.
+    /// </summary>
+    public class RingBuffer : IRingBuffer
+    {
+        private readonly byte[] _buffer;
+        private int _cursor;
+
+        public int BufferSize { get; }
+
+        public int Cursor => _cursor;
+
+        private readonly int _mask;
+
+        public RingBuffer(int size)
+        {
+            if ((size & (size - 1)) != 0)
+            {
+                throw new ArgumentException("RingArrayBuffer size must be a power of two");
+            }
+
+            BufferSize = size;
+            _buffer = new byte[size];
+            _cursor = 0;
+            _mask = size - 1;
+
+            // Fill with spaces
+            for (int i = 0; i < size; i++)
+            {
+                _buffer[i] = (byte)' ';
+            }
+        }
+
+        public void SetCursor(int pos)
+        {
+            _cursor = pos & _mask;
+        }
+
+        public void Push(byte value)
+        {
+            int index = _cursor;
+            _buffer[index & _mask] = value;
+            _cursor = (index + 1) & _mask;
+        }
+
+        public byte this[int index] => _buffer[index & _mask];
+
+        public HistoryIterator IterFromOffset(int offset)
+        {
+            int masked = (offset & _mask) + 1;
+            int startIndex = _cursor + BufferSize - masked;
+            return new HistoryIterator(this, startIndex);
+        }
+
+        public HistoryIterator IterFromPos(int pos)
+        {
+            int startIndex = pos & _mask;
+            return new HistoryIterator(this, startIndex);
+        }
+    }
+}

tests/SharpCompress.Test/Arj/ArjReaderTests.cs

@@ -22,6 +22,15 @@ namespace SharpCompress.Test.Arj
         [Fact]
         public void Arj_Uncompressed_Read() => Read("Arj.store.arj", CompressionType.None);
 
+        [Fact]
+        public void Arj_Method1_Read() => Read("Arj.method1.arj");
+
+        [Fact]
+        public void Arj_Method2_Read() => Read("Arj.method2.arj");
+
+        [Fact]
+        public void Arj_Method3_Read() => Read("Arj.method3.arj");
+
         [Fact]
         public void Arj_Method4_Read() => Read("Arj.method4.arj");