Function sift_down

src/fl/stl/algorithm.h:360–382

// Heapsort implementation (fallback for deep recursion)
template <typename Iterator, typename Compare>
void sift_down(Iterator first, Iterator start, Iterator end, Compare comp) FL_NOEXCEPT {
    Iterator root = start;
    
    while (root - first <= (end - first - 2) / 2) {
        Iterator child = first + 2 * (root - first) + 1;
        Iterator swap_iter = root;
        
        if (comp(*swap_iter, *child)) {
            swap_iter = child;
        }
        
        if (child + 1 <= end && comp(*swap_iter, *(child + 1))) {
            swap_iter = child + 1;
        }
        
        if (swap_iter == root) {
            return;
        } else {
            swap(*root, *swap_iter);
            root = swap_iter;
        }
    }
}

template <typename Iterator, typename Compare>
void heapify(Iterator first, Iterator last, Compare comp) FL_NOEXCEPT {