private void WriteCompressedBlockHeader(ReadOnlySpan <byte> input, Span <byte> output, int compressedSize)
{
var blockSize = compressedSize + 4; // CRC
BinaryPrimitives.WriteInt32LittleEndian(output.Slice(1), blockSize);
output[0] = (byte)Constants.ChunkType.CompressedData;
var crc = Crc32CAlgorithm.Compute(input);
crc = Crc32CAlgorithm.ApplyMask(crc);
BinaryPrimitives.WriteUInt32LittleEndian(output.Slice(4), crc);
}
public unsafe int Decompress(Span <byte> buffer)
{
Debug.Assert(_decompressor != null);
var chunkType = _chunkType;
var chunkSize = _chunkSize;
var chunkBytesProcessed = _chunkBytesProcessed;
fixed(byte *bufferStart = buffer)
{
var bufferEnd = bufferStart + buffer.Length;
var bufferPtr = bufferStart;
fixed(byte *inputStart = _input.Span)
{
var inputEnd = inputStart + _input.Length;
var inputPtr = inputStart;
while (bufferPtr < bufferEnd && (inputPtr < inputEnd || (chunkType == Constants.ChunkType.CompressedData && _decompressor.AllDataDecompressed)))
{
// ReSharper disable once SwitchStatementHandlesSomeKnownEnumValuesWithDefault
switch (chunkType)
{
case null:
// Not in a chunk, read the chunk type and size
var rawChunkHeader =
ReadChunkHeader(ref inputPtr, inputEnd);
if (rawChunkHeader == 0)
{
// Not enough data, get some more
break;
}
chunkType = (Constants.ChunkType)(rawChunkHeader & 0xff);
chunkSize = unchecked ((int)(rawChunkHeader >> 8));
chunkBytesProcessed = 0;
_scratchLength = 0;
_chunkCrc = 0;
break;
case Constants.ChunkType.CompressedData:
{
if (chunkBytesProcessed < 4)
{
_decompressor.Reset();
if (!ReadChunkCrc(ref inputPtr, inputEnd, ref chunkBytesProcessed))
{
// Incomplete CRC
break;
}
if (inputPtr >= inputEnd)
{
// No more data
break;
}
}
while (bufferPtr < bufferEnd && !_decompressor.EndOfFile)
{
if (_decompressor.NeedMoreData)
{
var availableInputBytes = unchecked ((int)(inputEnd - inputPtr));
if (availableInputBytes <= 0)
{
// No more data to give
break;
}
var availableChunkBytes = Math.Min(availableInputBytes,
chunkSize - chunkBytesProcessed);
Debug.Assert(availableChunkBytes > 0);
_decompressor.Decompress(new ReadOnlySpan <byte>(inputPtr, availableChunkBytes));
chunkBytesProcessed += availableChunkBytes;
inputPtr += availableChunkBytes;
}
var decompressedBytes = _decompressor.Read(new Span <byte>(bufferPtr,
unchecked ((int)(bufferEnd - bufferPtr))));
_chunkCrc = Crc32CAlgorithm.Append(_chunkCrc, new ReadOnlySpan <byte>(bufferPtr, decompressedBytes));
bufferPtr += decompressedBytes;
}
if (_decompressor.EndOfFile)
{
// Completed reading the chunk
chunkType = null;
var crc = Crc32CAlgorithm.ApplyMask(_chunkCrc);
if (_expectedChunkCrc != crc)
{
throw new InvalidDataException("Chunk CRC mismatch.");
}
}
break;
}
case Constants.ChunkType.UncompressedData:
{
if (chunkBytesProcessed < 4)
{
if (!ReadChunkCrc(ref inputPtr, inputEnd, ref chunkBytesProcessed))
{
// Incomplete CRC
break;
}
if (inputPtr >= inputEnd)
{
// No more data
break;
}
}
var chunkBytes = unchecked (Math.Min(Math.Min((int)(bufferEnd - bufferPtr), (int)(inputEnd - inputPtr)),
chunkSize - chunkBytesProcessed));
Unsafe.CopyBlockUnaligned(bufferPtr, inputPtr, unchecked ((uint)chunkBytes));
_chunkCrc = Crc32CAlgorithm.Append(_chunkCrc, new ReadOnlySpan <byte>(bufferPtr, chunkBytes));
bufferPtr += chunkBytes;
inputPtr += chunkBytes;
chunkBytesProcessed += chunkBytes;
if (chunkBytesProcessed >= chunkSize)
{
// Completed reading the chunk
chunkType = null;
var crc = Crc32CAlgorithm.ApplyMask(_chunkCrc);
if (_expectedChunkCrc != crc)
{
throw new InvalidDataException("Chunk CRC mismatch.");
}
}
break;
}
default:
{
if (chunkType < Constants.ChunkType.SkippableChunk)
{
throw new InvalidDataException($"Unknown chunk type {(int) chunkType:x}");
}
var chunkBytes = Math.Min(unchecked ((int)(inputEnd - inputPtr)), chunkSize - chunkBytesProcessed);
inputPtr += chunkBytes;
chunkBytesProcessed += chunkBytes;
if (chunkBytesProcessed >= chunkSize)
{
// Completed reading the chunk
chunkType = null;
}
break;
}
}
}
_chunkType = chunkType;
_chunkSize = chunkSize;
_chunkBytesProcessed = chunkBytesProcessed;
_input = _input.Slice(unchecked ((int)(inputPtr - inputStart)));
return(unchecked ((int)(bufferPtr - bufferStart)));
}
}
}