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