Re: [PATCH] x86_64: Add sinh with FMA

[Florian Weimer <fweimer@redhat.com>]

* H. J. Lu via Libc-alpha:

> On Wed, Aug 16, 2023 at 7:45 AM Paul Zimmermann
> <Paul.Zimmermann@inria.fr> wrote:
>>
>>        Hi H.J.,
>>
>> I get no improvement in accuracy. The largest known ulp error is still
>> the same:
>>
>> sinh 0 -1 -0x1.633c654fee2bap+9 [2] [1.93] 1.92222 1.922214006544865
>>
>> Maybe the FMA is not used for large inputs?
>>
>
> There is only one FMA insn in __ieee754_sinh_fma:
>
> 114: c4 e2 e9 9b 05 00 00 00 00 vfmsub132sd 0x0(%rip),%xmm2,%xmm0
>
> Since it calls __ieee754_exp and __expm1, with
>
> commit 1b214630ce6f7e0099b8b6f87246246739b079cf (master)
> Author: H.J. Lu <hjl.tools@gmail.com>
> Date:   Fri Aug 11 08:04:08 2023 -0700
>
>     x86_64: Add expm1 with FMA
>
>     On Skylake, it improves expm1 bench performance by:
>
>             Before       After     Improvement
>     max     70.204       68.054       3%
>     min     20.709       16.2         22%
>     mean    22.1221      16.7367      24%
>
> There is very little improvement with a single FMA insn.

If you specialize the implementation for FMA, could you avoid the
indirect call to __ieee754_exp and __expm1?

Thanks,
Florian