[PATCH 2/8] math: Optimize fma call on acospif

[Paul Zimmermann]

       Hi,

LGTM with one minor change below.

Tested by exhaustive test with all rounding modes, with the CORE-MATH
test suite and -march=x86-64-v2.

Reviewed-by: Paul Zimmermann <Paul.Zimmermann@inria.fr>

Paul

> From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> Cc: Wilco Dijkstra <Wilco.Dijkstra@arm.com>,
> 	Paul Zimmermann <Paul.Zimmermann@inria.fr>,
> 	DJ Delorie <dj@redhat.com>
> Date: Fri, 10 Oct 2025 14:49:20 -0300
> 
> The fma is required only for inputs less than 0x1.0fd288p-127.  Also
> only add the extra check for !__FP_FAST_FMA targets.
> 
> Checked on x86_64-linux-gnu and aarch64-linux-gnu.
> ---
>  sysdeps/ieee754/flt-32/s_acospif.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/sysdeps/ieee754/flt-32/s_acospif.c b/sysdeps/ieee754/flt-32/s_acospif.c
> index caf65d42f3d..63230bd3b37 100644
> --- a/sysdeps/ieee754/flt-32/s_acospif.c
> +++ b/sysdeps/ieee754/flt-32/s_acospif.c
> @@ -67,7 +67,12 @@ __acospif (float x)
>        /* For |x| <= 0x1.0fd288p-127, c0 += c4*(z4*z4) would raise a spurious
>  	 underflow exception, we use an FMA instead, where c4 * z4 does not
>  	 underflow. */
> -      c0 = fma (c4 * z4, z4, c0);
> +#ifndef __FP_FAST_FMA
> +      if (__glibc_likely (ax > 0x1.0fd288p-127))

should be 0x1.0fd288p-127f (ax is a float)

> +	c0 = (c4 * z4) * z4 + c0;
> +      else
> +#endif
> +	c0 = fma (c4 * z4, z4, c0);
>        return 0.5 - z * c0;
>      }
>    else
> -- 
> 2.43.0
> 
>