code: @Deprecated
    public static int cardinalityInBitmapWordRange(long[] bitmap, int start, int end) {
      if (start >= end) {
        return 0;
      }
      int firstword = start / 64;
      int endword = (end - 1) / 64;
      int answer = 0;
      for (int i = firstword; i <= endword; i++) {
        answer += Long.bitCount(bitmap[i]);
      }
      return answer;
    }
docs: Hamming weight of the 64-bit words involved in the range
  start, start+1,..., end-1, that is, it will compute the
  cardinality of the bitset from index (floor(start/64) to floor((end-1)/64))
  inclusively.
  
  @param bitmap array of words representing a bitset
  @param start first index  (inclusive)
  @param end last index (exclusive)
  @return the hamming weight of the corresponding words