[PATCH v2] Improves __ieee754_exp(x) performance by 18-37% when |x| < 1.0397

[Szabolcs Nagy]

On 06/04/18 21:58, Patrick McGehearty wrote:
> Adds a fast path to e_exp.c when |x| < 1.03972053527832.
> When values are tested in isolation, reduction in execution
> time is: aarch 30%, sparc 18%, x86 37%.
> When comparing benchtests/bench.out which includes values
> outside that range, the gains are:
> aarch 8%, sparc 5%, x86 9%.
> 
> make check is clean (no increase in ulp for any math test).
> Testing 20M values for each rounding mode in that range shows
> approximately one in 200 values is off by 1 ulp. No value tested
> for exp(x) changed by 2 or more ulp.
> 
> No observed change in performance or accuracy for x outside
> fast path range.
> 
> These changes will be active for all platforms that don't provide
> their own exp() routines. They will also be active for ieee754
> versions of ccos, ccosh, cosh, csin, csinh, sinh, exp10, gamma, and
> erf.
> 
> New in this version:
> Copyright year for eexp.tbl changed from 2017 to 2018.
> Spurious white space diff e_exp.c removed.
> 
> ChangeLog:
> 2018-03-20  Patrick McGehearty <patrick.mcgehearty@oracle.com>
> 
>          * sysdeps/ieee754/dbl-64/e_exp.c: faster __ieee754_exp()
>          * sysdeps/ieee754/dbl-64/eexp.tbl: New file for e_exp.c

looks ok to me.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>