docs: public void flip(final int x) {
      final short hb = Util.highbits(x);
      final int i = highLowContainer.getIndex(hb);
      if (i >= 0) {
        Container c = highLowContainer.getContainerAtIndex(i).flip(Util.lowbits(x));
        if (!c.isEmpty()) {
          highLowContainer.setContainerAtIndex(i, c);
        } else {
          highLowContainer.removeAtIndex(i);
        }
      } else {
        final ArrayContainer newac = new ArrayContainer();
        highLowContainer.insertNewKeyValueAt(-i - 1, hb, newac.add(Util.lowbits(x)));
      }
    }