Method decodeContextMap

java/org/brotli/dec/Decode.java:666–730

(int contextMapSize, byte[] contextMap, State s)

  }

  private static int decodeContextMap(int contextMapSize, byte[] contextMap, State s) {
    int result;
    if (s.halfOffset > BitReader.HALF_WATERLINE) {
      result = BitReader.readMoreInput(s);
      if (result < BROTLI_OK) {
        return result;
      }
    }
    final int numTrees = decodeVarLenUnsignedByte(s) + 1;

    if (numTrees == 1) {
      Utils.fillBytesWithZeroes(contextMap, 0, contextMapSize);
      return numTrees;
    }

    BitReader.fillBitWindow(s);
    final int useRleForZeros = BitReader.readFewBits(s, 1);
    int maxRunLengthPrefix = 0;
    if (useRleForZeros != 0) {
      maxRunLengthPrefix = BitReader.readFewBits(s, 4) + 1;
    }
    final int alphabetSize = numTrees + maxRunLengthPrefix;
    final int tableSize = MAX_HUFFMAN_TABLE_SIZE[(alphabetSize + 31) >> 5];
    /* Speculative single entry table group. */
    final int[] table = new int[tableSize + 1];
    final int tableIdx = table.length - 1;
    result = readHuffmanCode(alphabetSize, alphabetSize, table, tableIdx, s);
    if (result < BROTLI_OK) {
      return result;
    }
    int i = 0;
    while (i < contextMapSize) {
      if (s.halfOffset > BitReader.HALF_WATERLINE) {
        result = BitReader.readMoreInput(s);
        if (result < BROTLI_OK) {
          return result;
        }
      }
      BitReader.fillBitWindow(s);
      final int code = readSymbol(table, tableIdx, s);
      if (code == 0) {
        contextMap[i] = 0;
        i++;
      } else if (code <= maxRunLengthPrefix) {
        BitReader.fillBitWindow(s);
        int reps = (1 << code) + BitReader.readFewBits(s, code);
        while (reps != 0) {
          if (i >= contextMapSize) {
            return Utils.makeError(s, BROTLI_ERROR_CORRUPTED_CONTEXT_MAP);
          }
          contextMap[i] = 0;
          i++;
          reps--;
        }
      } else {
        contextMap[i] = (byte) (code - maxRunLengthPrefix);
        i++;
      }