public void set(int index) {
    int wordNum = index >> 6;      // div 64
    int bit = index & 0x3f;     // mod 64
    long bitmask = 1L << bit;
    bits[wordNum / PAGE_SIZE][wordNum % PAGE_SIZE] |= bitmask;
  }
Sets the bit at the specified index.
The index should be less than the OpenBitSet size.
ambry-utils/src/main/java/com/github/ambry/utils/OpenBitSet.java