readBits method

int readBits(int numBits)

Implementation

int readBits(int numBits) {
  if (numBits < 1 || numBits > 32 || numBits > available) throw const UCodeDecodeException("Bit source overrun");
  int result = 0;
  int remaining = numBits;

  if (_bitOffset > 0) {
    final int bitsLeft = 8 - _bitOffset;
    final int toRead = remaining < bitsLeft ? remaining : bitsLeft;
    final int bitsToNotRead = bitsLeft - toRead;
    final int mask = (0xFF >> (8 - toRead)) << bitsToNotRead;
    result = (bytes[_byteOffset] & mask) >> bitsToNotRead;
    remaining -= toRead;
    _bitOffset += toRead;
    if (_bitOffset == 8) {
      _bitOffset = 0;
      _byteOffset++;
    }
  }

  if (remaining > 0) {
    while (remaining >= 8) {
      result = (result << 8) | (bytes[_byteOffset] & 0xFF);
      _byteOffset++;
      remaining -= 8;
    }
    if (remaining > 0) {
      final int bitsToNotRead = 8 - remaining;
      final int mask = (0xFF >> bitsToNotRead) << bitsToNotRead;
      result = (result << remaining) | ((bytes[_byteOffset] & mask) >> bitsToNotRead);
      _bitOffset += remaining;
    }
  }
  return result;
}