This patch completes the implementation of simd<> and related operations.
A few nits, a bit of things moving underneath you, but this looks good.
Need to add more stuff to the tests ;-)
In the TS, hmin, hmax (and a bunch of others) are noexcept. This was added in P1110, in response to NB comments CH 30 and CH 33.
Need to fix that here, and add ASSERT_NOEXCEPT to a bunch of tests.
We're going to need a lot of _LIBCPP_TYPE_VIS and other annotations. That can be a separate patch, though
I don't think that auto buys you anything here. simd is fine, and no longer.
Check the return types here with ASSERT_SAME_TYPE