// 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); }
internal static void WriteMatch(int matchLen, int matchPos, OutputBuffer output) { Debug.Assert(matchLen >= FastEncoderWindow.MinMatch && matchLen <= FastEncoderWindow.MaxMatch, "Illegal currentMatch length!"); Debug.WriteLineIf(CompressionTracingSwitch.Verbose, String.Format(CultureInfo.InvariantCulture, "Match: {0}:{1}", matchLen, matchPos), "Compression"); // 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]); } }