code: public static void set(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);
      Platform.putLong(baseObject, wordOffset, word | mask);
    }
docs: Sets the bit at the specified index to {@code true}.