tree ad65a58d8a0bce077530d7ed68b45dadc0ec7549
parent 56dcf6d8dc7428d6587dec37d6f439b1cdf9c061
author Arthur O'Dwyer <arthur.j.odwyer@gmail.com> 1608183602 -0500
committer Copybara-Service <copybara-worker@google.com> 1611866093 -0800

[libc++] [P0879] constexpr std::nth_element, and rewrite its tests.

This patch is more than just adding the `constexpr` keyword, because
the old code relied on `goto`, and `goto` is not constexpr-friendly.
Refactor to eliminate `goto`, and then mark it as constexpr in C++20.

I freely admit that the name `__nth_element_partloop` is bad;
I couldn't find any better name because I don't really know
what this loop is doing, conceptually. Vice versa, I think
`__nth_element_find_guard` has a decent name.

Now the only one we're still missing from P0879 is `sort`.

Differential Revision: https://reviews.llvm.org/D93557

GitOrigin-RevId: 207d4be4d9d39fbb9aca30e5d5d11245db9bccc1