Re: [PATCH] Improves __ieee754_exp() performance by 2x-5x on sparc/x86.

[Patrick McGehearty <patrick dot mcgehearty at oracle dot com>]

On 1/3/2018 1:28 PM, Patrick McGehearty wrote:
> Version 10 of proposed patch.
>
> Add removal of sysdeps/i386/fpu/slowexp.c, sysdeps/ia64/fpu/slowexp.c
> and sysdeps/m68k/m680x0/fpu/slowexp.c as building of slowexp.c no
> longer needs to be overriden in these architectures.
>
> Reverted eexp.tbl to 64 entries for scaling table and changed back to
> invln2_64, ln2_64hi, ln2_64lo. Reduces L1 cache impact of table at
> cost of increasing frequency of 1 ulp differences from old method.
>
> Cleaned up trailing white space in e_exp.c
>
> Performance gain for typical values is 2x on Sparc and 5x on x86.
> SET_RESTORE_ROUND is particularly slow on Sparc.  Investigating the
> root cause is out of scope for this patch, but worthy of later study
> as the same issue may be seen elsewhere.  For those values which
> triggered calls to "slowexp" in the previous algorithm, the speedup on
> both Sparc and x86 is over 100x. Over a range of randomly generated
> values, these slow cases are rare but have been reported to be notable
> in some applications.
Here is the proposed change log to go with patch version 10.
It includes the files overlooked in patch version 8.

2017-12-19  Patrick McGehearty <patrick.mcgehearty@oracle.com>

        * sysdeps/ieee754/dbl-64/e_exp.c: 5x faster __ieee754_exp() 
routine.
        * sysdeps/ieee754/dbl-64/eexp.tbl: New file for e_exp.
        * sysdeps/ieee754/dbl-64/slowexp.c: Removed.
        * sysdeps/i386/fpu/slowexp.c: Removed.
        * sysdeps/ia64/fpu/slowexp.c: Removed.
        * sysdeps/m68k/m680x0/fpu/slowexp.c: Removed.
        * sysdeps/x86_64/fpu/multiarch/slowexp-avx.c: Removed.
        * sysdeps/x86_64/fpu/multiarch/slowexp-fma.c: Removed.
        * sysdeps/x86_64/fpu/multiarch/slowexp-fma4.c: Removed.
        * sysdeps/generic/math_private.h: Remove slowexp.
        * sysdeps/ieee754/dbl-64/e_pow.c: Likewise.
        * sysdeps/powerpc/power4/fpu/Makefile: Likewise.
        * sysdeps/x86_64/fpu/multiarch/Makefile: Likewise.
        * sysdeps/x86_64/fpu/multiarch/e_exp-avx.c: Likewise.
        * sysdeps/x86_64/fpu/multiarch/e_exp-fma.c: Likewise.
        * sysdeps/x86_64/fpu/multiarch/e_exp-fma4.c: Likewise.
        * math/Makefile: Likewise.
        * manual/probes.texi: Remove slowexp documentation.