// Calculate the huffman code for each character based on the code length for each character.
// This algorithm is described in standard RFC 1951
uint[] CalculateHuffmanCode()
{
uint[] bitLengthCount = new uint[17];
foreach (int codeLength in codeLengthArray)
{
bitLengthCount[codeLength]++;
}
bitLengthCount[0] = 0; // clear count for length 0
uint[] nextCode = new uint[17];
uint tempCode = 0;
for (int bits = 1; bits <= 16; bits++)
{
tempCode = (tempCode + bitLengthCount[bits - 1]) << 1;
nextCode[bits] = tempCode;
}
uint[] code = new uint[MaxLiteralTreeElements];
for (int i = 0; i < codeLengthArray.Length; i++)
{
int len = codeLengthArray[i];
if (len > 0)
{
code[i] = FastEncoderStatics.BitReverse(nextCode[len], len);
nextCode[len]++;
}
}
return(code);
}
static internal void WriteMatch(int matchLen, int matchPos, OutputBuffer output)
{
Debug.Assert(matchLen >= FastEncoderWindow.MinMatch && matchLen <= FastEncoderWindow.MaxMatch, "Illegal currentMatch length!");
// Get the code information for a match code
uint codeInfo = FastEncoderStatics.FastEncoderLiteralCodeInfo[(FastEncoderStatics.NumChars + 1 - FastEncoderWindow.MinMatch) + matchLen];
int codeLen = (int)codeInfo & 31;
Debug.Assert(codeLen != 0, "Invalid Match Length!");
if (codeLen <= 16)
{
output.WriteBits(codeLen, codeInfo >> 5);
}
else
{
output.WriteBits(16, (codeInfo >> 5) & 65535);
output.WriteBits(codeLen - 16, codeInfo >> (5 + 16));
}
// Get the code information for a distance code
codeInfo = FastEncoderStatics.FastEncoderDistanceCodeInfo[FastEncoderStatics.GetSlot(matchPos)];
output.WriteBits((int)(codeInfo & 15), codeInfo >> 8);
int extraBits = (int)(codeInfo >> 4) & 15;
if (extraBits != 0)
{
output.WriteBits(extraBits, (uint)matchPos & FastEncoderStatics.BitMask[extraBits]);
}
}