Function lower_bound_impl

src/fl/stl/algorithm.h:442–455

// Find the position where value should be inserted in sorted range [first, last)
template <typename Iterator, typename T, typename Compare>
Iterator lower_bound_impl(Iterator first, Iterator last, const T& value, Compare comp) FL_NOEXCEPT {
    auto count = last - first;
    while (count > 0) {
        auto step = count / 2;
        Iterator it = first + step;
        if (comp(*it, value)) {
            first = ++it;
            count -= step + 1;
        } else {
            count = step;
        }
    }
    return first;
}

// In-place merge operation for merge sort (stable sort)
template <typename Iterator, typename Compare>