[COMMITTED] arm: update libm test ulps

[Joseph Myers]

On Tue, 13 Apr 2021, Adhemerval Zanella via Libc-alpha wrote:

> The math/libm-test-support.c imposes maximum ulp limits depending of 
> the underling type:
> 
>  228   if (testing_ibm128)
>  229     /* The documented accuracy of IBM long double division is 3ulp
>  230        (see libgcc/config/rs6000/ibm-ldouble-format), so do not
>  231        require better accuracy for libm functions that are exactly
>  232        defined for other formats.  */
>  233     max_valid_error = exact ? 3 : 16;
>  234   else
>  235     max_valid_error = exact ? 0 : 9;
> 
> And if I recall correctly there was a suggestion to consolidate and/or
> remove the ulps file altogether and use the maximum valid error as the
> threshold to report regressions.  The only drawback I see of moving
> towards it is each architecture won't see if some change has degraded
> the function precision.

And for some of the higher ulps values it might be good to improve the 
precision, which suggests having at least per-format if not 
per-architecture empirical bounds for each function.

-- 
Joseph S. Myers
joseph@codesourcery.com