code: public static boolean isSet(Object baseObject, long baseOffset, int index) {
      assert index >= 0 : "index (" + index + ") should >= 0";
      final long mask = 1L << (index & 0x3f);  // mod 64 and shift
      final long wordOffset = baseOffset + (index >> 6) * WORD_SIZE;
      final long word = Platform.getLong(baseObject, wordOffset);
      return (word & mask) != 0;
    }
docs: Returns {@code true} if the bit is set at the specified index.