Method check

src/test/java/org/mapdb/BTreeSet2Test.java:868–979

(NavigableSet<Integer> set,
               final int min, final int max, final boolean ascending,
               final BitSet bs)

     * min and max are both inclusive.  If max < min, interval is empty.
     */
    void check(NavigableSet<Integer> set,
               final int min, final int max, final boolean ascending,
               final BitSet bs) {
        class ReferenceSet {
            int lower(int element) {
                return ascending ?
                        lowerAscending(element) : higherAscending(element);
            }
            int floor(int element) {
                return ascending ?
                        floorAscending(element) : ceilingAscending(element);
            }
            int ceiling(int element) {
                return ascending ?
                        ceilingAscending(element) : floorAscending(element);
            }
            int higher(int element) {
                return ascending ?
                        higherAscending(element) : lowerAscending(element);
            }
            int first() {
                return ascending ? firstAscending() : lastAscending();
            }
            int last() {
                return ascending ? lastAscending() : firstAscending();
            }
            int lowerAscending(int element) {
                return floorAscending(element - 1);
            }
            int floorAscending(int element) {
                if (element < min)
                    return -1;
                else if (element > max)
                    element = max;

                // BitSet should support this! Test would run much faster
                while (element >= min) {
                    if (bs.get(element))
                        return element;
                    element--;
                }
                return -1;
            }
            int ceilingAscending(int element) {
                if (element < min)
                    element = min;
                else if (element > max)
                    return -1;
                int result = bs.nextSetBit(element);
                return result > max ? -1 : result;
            }
            int higherAscending(int element) {
                return ceilingAscending(element + 1);
            }
            private int firstAscending() {
                int result = ceilingAscending(min);
                return result > max ? -1 : result;
            }