code: @Deprecated
    private static int cardinalityInBitmapWordRange(LongBuffer bitmap, int start, int end) {
      if (isBackedBySimpleArray(bitmap)) {
        return Util.cardinalityInBitmapWordRange(bitmap.array(), start, 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.get(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