[PATCH] [libc++] Fix std::make_heap's worst case time complexity

[David Majnemer]

Ping.

On Wed, Jul 9, 2014 at 3:14 AM, David Majnemer <david.majnemer at gmail.com> wrote:
> std::make_heap is currently implemented by iteratively applying a
> sift_up-type algorithm.
> Since sift-up is O(ln n), this gives std::make_heap a worst case time
> complexity of O(n ln n).  Since the C++ standard mandates that
> std::make_heap make no more than O(3n) comparisons, this makes our
> std::make_heap out of spec.
>
> Fix this by introducing an implementation of __sift_down and switch
> std::make_heap to create the heap using it.  This gives std::make_heap
> linear time complexity in the worst case.
>
> This fixes PR20161.