docs: public boolean checkedAdd(final int x) {
      final short hb = BufferUtil.highbits(x);
      final int i = highLowContainer.getIndex(hb);
      if (i >= 0) {
        MappeableContainer C = highLowContainer.getContainerAtIndex(i);
        int oldcard = C.getCardinality();
        C = C.add(BufferUtil.lowbits(x));
        getMappeableRoaringArray().setContainerAtIndex(i, C);
        return C.getCardinality() > oldcard;
      } else {
        final MappeableArrayContainer newac = new MappeableArrayContainer();
        getMappeableRoaringArray().insertNewKeyValueAt(-i - 1, hb, newac.add(BufferUtil.lowbits(x)));
        return true;
      }
    }