docs: public boolean contains(RoaringBitmap subset) {
      if(subset.getCardinality() > getCardinality()) {
        return false;
      }
      final int length1 = this.highLowContainer.size;
      final int length2 = subset.highLowContainer.size;
      int pos1 = 0, pos2 = 0;
      while (pos1 < length1 && pos2 < length2) {
        final short s1 = this.highLowContainer.getKeyAtIndex(pos1);
        final short s2 = subset.highLowContainer.getKeyAtIndex(pos2);
        if (s1 == s2) {
          Container c1 = this.highLowContainer.getContainerAtIndex(pos1);
          Container c2 = subset.highLowContainer.getContainerAtIndex(pos2);
          if(!c1.contains(c2)) {
            return false;
          }
          ++pos1;
          ++pos2;
        } else if (Util.compareUnsigned(s1, s2) > 0) {
          return false;
        } else {
          pos1 = subset.highLowContainer.advanceUntil(s2, pos1);
        }
      }
      return pos2 == length2;
    }