[libcxx-commits] [PATCH] D96084: Revert "Revert "[libc++] [P0879] constexpr std::nth_element, and rewrite its tests.""

[Arthur O'Dwyer via Phabricator via libcxx-commits]

Quuxplusone planned changes to this revision.
Quuxplusone added a comment.

> Simple "manual" tests can also pay off :-)

Well, actually, before landing this I thought I'd better run some more randomized tests... and I found that this patch //also// has a bug somewhere!  Reduced from the randomized tests:

  std::vector<int> v2 = { 18, -7, 1, -9, 3, 13, -10, -10, -9, 4, -10, 5, 8, 6, 11, -10, 19 };
  std::nth_element(v2.begin(), v2.begin() + 10, v2.end());
  assert(std::all_of(v2.begin(), v2.begin() + 10, [&](int x){ return x <= v2[10]; }));
  assert(std::all_of(v2.begin() + 10, v2.end(), [&](int x){ return x >= v2[10]; }));  // fails!

So I'm still working on this.


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  https://reviews.llvm.org/D96084/new/

https://reviews.llvm.org/D96084