IndexedSorter check bound

[cddesire]

given range of items using heap sort

private static void downHeap(final IndexedSortable s, final int b,
      int i, final int N) {
    for (int idx = i << 1; idx < N; idx = i << 1) {
      if (idx + 1 < N && s.compare(b + idx, b + idx + 1) < 0) {
        if (s.compare(b + i, b + idx + 1) < 0) {
          s.swap(b + i, b + idx + 1);
        } else return;
        i = idx + 1;
      } else if (s.compare(b + i, b + idx) < 0) {
        s.swap(b + i, b + idx);
        i = idx;
      } else return;
    }
  }