createHuffmanDecodingTables() — netty Function Reference

Source Code

codec-compression/src/main/java/io/netty/handler/codec/compression/Bzip2HuffmanStageDecoder.java lines 117–167

    void createHuffmanDecodingTables() {
        final int alphabetSize = this.alphabetSize;

        for (int table = 0; table < tableCodeLengths.length; table++) {
            final int[] tableBases = codeBases[table];
            final int[] tableLimits = codeLimits[table];
            final int[] tableSymbols = codeSymbols[table];
            final byte[] codeLengths = tableCodeLengths[table];

            int minimumLength = HUFFMAN_DECODE_MAX_CODE_LENGTH;
            int maximumLength = 0;

            // Find the minimum and maximum code length for the table
            for (int i = 0; i < alphabetSize; i++) {
                final byte currLength = codeLengths[i];
                maximumLength = Math.max(currLength, maximumLength);
                minimumLength = Math.min(currLength, minimumLength);
            }
            minimumLengths[table] = minimumLength;

            // Calculate the first output symbol for each code length
            for (int i = 0; i < alphabetSize; i++) {
                tableBases[codeLengths[i] + 1]++;
            }
            for (int i = 1, b = tableBases[0]; i < HUFFMAN_DECODE_MAX_CODE_LENGTH + 2; i++) {
                b += tableBases[i];
                tableBases[i] = b;
            }

            // Calculate the first and last Huffman code for each code length (codes at a given
            // length are sequential in value)
            for (int i = minimumLength, code = 0; i <= maximumLength; i++) {
                int base = code;
                code += tableBases[i + 1] - tableBases[i];
                tableBases[i] = base - tableBases[i];
                tableLimits[i] = code - 1;
                code <<= 1;
            }

            // Populate the mapping from canonical code index to output symbol
            for (int bitLength = minimumLength, codeIndex = 0; bitLength <= maximumLength; bitLength++) {
                for (int symbol = 0; symbol < alphabetSize; symbol++) {
                    if (codeLengths[symbol] == bitLength) {
                        tableSymbols[codeIndex++] = symbol;
                    }
                }
            }
        }

        currentTable = selectors[0];
    }