// Section 2.4.1.3.19.3
// page 69, 70
private static CopyToken PackCopyToken(byte[] Data, DecompressionState state, UInt16 Offset, UInt16 Length)
{
var help = CopyToken.CopyTokenHelp(state.DecompressedCurrent, state.DecompressedChunkStart);
var temp1 = (ushort)(Offset - 1);
var temp2 = (ushort)(16 - help.BitCount);
var temp3 = (ushort)(Length - 3);
UInt16 TokenAsUInt16 = (UInt16)(((ushort)(temp1 << temp2)) | temp3);
var result = new CopyToken(TokenAsUInt16);
return(result);
}
// Section 2.4.1.3.19.4
// page 70
private static MatchingResult Matching(byte[] Data, DecompressionState state, int DecompressedEnd)
{
int Candidate = state.DecompressedCurrent - 1;
UInt16 BestLength = 0;
int BestCandidate = 0;
UInt16 Offset;
UInt16 Length;
while (Candidate >= state.DecompressedChunkStart)
{
int C = Candidate;
int D = state.DecompressedCurrent;
UInt16 Len = 0;
while (D < DecompressedEnd && Data[D] == Data[C])
{
++Len;
++C;
++D;
}
if (Len > BestLength)
{
BestLength = Len;
BestCandidate = Candidate;
}
--Candidate;
}
if (BestLength >= 3)
{
ushort MaximumLength = CopyToken.CopyTokenHelp(state.DecompressedCurrent, state.DecompressedChunkStart).MaximumLength;
Length = Math.Min(BestLength, MaximumLength);
Offset = (UInt16)(state.DecompressedCurrent - BestCandidate);
}
else
{
Length = 0;
Offset = 0;
}
return(new MatchingResult(Offset, Length));
}
public TokenSequence(XlBinaryReader CompressedData, int remainingBytes)
{
this.FlagByte = CompressedData.ReadByte();
--remainingBytes;
for (int i = 0; i < 8; i++)
{
if (remainingBytes == 0)
{
break;
}
//int index = (i - 7) * (-1); // The most significant byte describes the first token. The second most significant byte the second token. etc. So we map 0 -> 7, 1 -> 6, 2 -> 5, 3 -> 4, 4 -> 3, 5 -> 2, 6 -> 1, 7 -> 0
TokenType tokenType = GetTokenTypeAtIndex(i);
if (tokenType == TokenType.CopyToken)
{
var token = new CopyToken(CompressedData);
this._Tokens.Add(token);
remainingBytes -= token.GetSizeInBytes();
}
else if (tokenType == TokenType.LiteralToken)
{
var token = new LiteralToken(CompressedData);
this._Tokens.Add(token);
remainingBytes -= token.GetSizeInBytes();
}
else
{
throw new Exception();
}
// todo: last token sequence could contain less than 8 tokens
}
}
