private VCDiffResult DecodeCore()
{
using ByteBuffer instructionBuffer = new ByteBuffer(window.InstructionsAndSizesData);
using ByteBuffer addressBuffer = new ByteBuffer(window.AddressesForCopyData);
using ByteBuffer addRunBuffer = new ByteBuffer(window.AddRunData);
InstructionDecoder instrDecoder = new InstructionDecoder(instructionBuffer, customTable);
VCDiffResult result = VCDiffResult.SUCCESS;
while (this.TotalBytesDecoded < window.TargetWindowLength)
{
VCDiffInstructionType instruction = instrDecoder.Next(out int decodedSize, out byte mode);
switch (instruction)
{
case VCDiffInstructionType.EOD:
targetData.SetLength(0);
return(VCDiffResult.EOD);
case VCDiffInstructionType.ERROR:
targetData.SetLength(0);
return(VCDiffResult.ERROR);
}
switch (instruction)
{
case VCDiffInstructionType.ADD:
result = DecodeAdd(decodedSize, addRunBuffer);
break;
case VCDiffInstructionType.RUN:
result = DecodeRun(decodedSize, addRunBuffer);
break;
case VCDiffInstructionType.COPY:
result = DecodeCopy(decodedSize, mode, addressBuffer);
break;
default:
targetData.SetLength(0);
return(VCDiffResult.ERROR);
}
}
if (window.ChecksumFormat == ChecksumFormat.SDCH)
{
uint adler = Checksum.ComputeGoogleAdler32(targetData.GetBuffer().AsMemory(0, (int)targetData.Length));
if (adler != window.Checksum)
{
result = VCDiffResult.ERROR;
}
}
else if (window.ChecksumFormat == ChecksumFormat.Xdelta3)
{
uint adler = Checksum.ComputeXdelta3Adler32(targetData.GetBuffer().AsMemory(0, (int)targetData.Length));
if (adler != window.Checksum)
{
result = VCDiffResult.ERROR;
}
}
return(result);
}
/// <summary>
/// Encodes the data using the settings from initialization
/// </summary>
/// <param name="newData">the target data</param>
/// <param name="outputStream">the out stream</param>
public unsafe void EncodeChunk(ByteBuffer newData, Stream outputStream)
{
newData.Position = 0;
ReadOnlyMemory <byte> checksumBytes = newData.ReadBytes((int)newData.Length);
uint checksum = this.checksumFormat switch
{
ChecksumFormat.SDCH => Checksum.ComputeGoogleAdler32(checksumBytes),
ChecksumFormat.Xdelta3 => Checksum.ComputeXdelta3Adler32(checksumBytes),
ChecksumFormat.None => 0,
_ => 0
};
windowEncoder = new WindowEncoder(oldData.Length, checksum, this.checksumFormat, this.interleaved);
oldData.Position = 0;
newData.Position = 0;
long nextEncode = newData.Position;
long targetEnd = newData.Length;
long startOfLastBlock = targetEnd - this.dictionary.blockSize;
long candidatePos = nextEncode;
ulong hash;
//create the first hash
hash = hasher.Hash(newData.DangerousGetBytePointerAtCurrentPositionAndIncreaseOffsetAfter(0),
this.dictionary.blockSize);
byte *newDataPtr = newData.DangerousGetBytePointer();
while (true)
{
//if less than block size exit and then write as an ADD
if (newData.Length - nextEncode < this.dictionary.blockSize)
{
break;
}
//try and encode the copy and add instructions that best match
var bytesEncoded = EncodeCopyForBestMatch(hash, candidatePos, nextEncode, targetEnd, newDataPtr, newData);
if (bytesEncoded > 0)
{
nextEncode += bytesEncoded;
candidatePos = nextEncode;
if (candidatePos > startOfLastBlock)
{
break;
}
newData.Position = candidatePos;
//cannot use rolling hash since we skipped so many
hash = hasher.Hash(newData.DangerousGetBytePointerAtCurrentPositionAndIncreaseOffsetAfter(this.dictionary.blockSize), this.dictionary.blockSize);
}
else
{
if (candidatePos + 1 > startOfLastBlock)
{
break;
}
//update hash requires the first byte of the last hash as well as the byte that is first byte pos + blockSize
//in order to properly calculate the rolling hash
newData.Position = candidatePos;
byte peek0 = newData.ReadByte();
newData.Position = candidatePos + this.dictionary.blockSize;
byte peek1 = newData.ReadByte();
hash = hasher.UpdateHash(hash, peek0, peek1);
candidatePos++;
}
}
//Add the rest of the data that was not encoded
if (nextEncode < newData.Length)
{
int len = (int)(newData.Length - nextEncode);
newData.Position = nextEncode;
windowEncoder.Add(newData.ReadBytes(len).Span);
}
//output the final window
windowEncoder.Output(outputStream);
}