Function decodeContextMap

js/decode.ts:471–544

(contextMapSize: number, contextMap: Int8Array, s: State)

  return readComplexHuffmanCode(alphabetSizeLimit, simpleCodeOrSkip, tableGroup, tableIdx, s);
}
function decodeContextMap(contextMapSize: number, contextMap: Int8Array, s: State): number {
  let result: number;
  if (s.halfOffset > 2030) {
    result = readMoreInput(s);
    if (result < 0) {
      return result;
    }
  }
  const numTrees: number = decodeVarLenUnsignedByte(s) + 1;
  if (numTrees === 1) {
    contextMap.fill(0, 0, contextMapSize);
    return numTrees;
  }
  if (s.bitOffset >= 16) {
    s.accumulator32 = (s.shortBuffer[s.halfOffset++] << 16) | (s.accumulator32 >>> 16);
    s.bitOffset -= 16;
  }
  const useRleForZeros: number = readFewBits(s, 1);
  let maxRunLengthPrefix = 0;
  if (useRleForZeros !== 0) {
    maxRunLengthPrefix = readFewBits(s, 4) + 1;
  }
  const alphabetSize: number = numTrees + maxRunLengthPrefix;
  const tableSize: number = MAX_HUFFMAN_TABLE_SIZE[(alphabetSize + 31) >> 5];
  const table = new Int32Array(tableSize + 1);
  const tableIdx: number = table.length - 1;
  result = readHuffmanCode(alphabetSize, alphabetSize, table, tableIdx, s);
  if (result < 0) {
    return result;
  }
  let i = 0;
  while (i < contextMapSize) {
    if (s.halfOffset > 2030) {
      result = readMoreInput(s);
      if (result < 0) {
        return result;
      }
    }
    if (s.bitOffset >= 16) {
      s.accumulator32 = (s.shortBuffer[s.halfOffset++] << 16) | (s.accumulator32 >>> 16);
      s.bitOffset -= 16;
    }
    const code: number = readSymbol(table, tableIdx, s);
    if (code === 0) {
      contextMap[i] = 0;
      i++;
    } else if (code <= maxRunLengthPrefix) {
      if (s.bitOffset >= 16) {
        s.accumulator32 = (s.shortBuffer[s.halfOffset++] << 16) | (s.accumulator32 >>> 16);
        s.bitOffset -= 16;
      }
      let reps: number = (1 << code) + readFewBits(s, code);
      while (reps !== 0) {
        if (i >= contextMapSize) {
          return makeError(s, -3);
        }
        contextMap[i] = 0;
        i++;