@Override
  public long get(int id) {
    assert id >= 0 : id;
    int bitIndex = id / chunksPerWord * ConcurrentBitSetImpl.BITS_PER_WORD + (id % chunksPerWord) * bitsPerChunk;
    return Integer.toUnsignedLong( (bits.getWord(bitIndex) >> bitIndex) & mask );
  }
@Override
  public long get(int id)