[libc-commits] [libc] [libc][math][c23] Add acospif16() function (PR #134664)

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amemov wrote:

@lntue - everything works right now and passes all the checks. 

I do have a question - would the current workaround for mpfr_acospi be acceptable, or should I optimize it further following the [internal implementation of the mpfr_acospi ](https://gitlab.inria.fr/mpfr/mpfr/-/blob/master/src/acosu.c)function by MPFR?

https://github.com/llvm/llvm-project/pull/134664