[RFC] [BZ15384] Enchance finite and isfinite.

[Ondřej Bílka]

On Sun, Apr 21, 2013 at 03:35:19PM +0200, Marc Glisse wrote:
> On Sun, 21 Apr 2013, Ondřej Bílka wrote:
> >However on x64 even gcc without optimizations expands finite to inline
> >version which is slower than my version(see benchmark).
> 
> This seems to depend on the CPU. Here:
> model name	: Intel(R) Core(TM)2 Duo CPU     T9600  @ 2.80GHz
>
Cannot duplicate 
on Intel(R) Core(TM)2 Quad  CPU   Q9300  @ 2.50GHz
and  Intel(R) Core(TM)2 Duo CPU     E7200  @ 2.53GHz
Could you try to run new version again?

However on AMD Phenom(tm) II X6 1090T Processor my results are below.

I fixed few mistakes in benchmark, now there should be correct version.
One problem is that we are affected by gcc bugs, particulary
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54349

Other explanation may be due bug in gcc that aligns loops only to 8
bytes. One implementation can get faster just because it is 16 byte
aligned so I changed that in assembly.


current

real	0m0.816s
user	0m0.813s
sys	0m0.000s

new # from mail


real	0m0.738s
user	0m0.737s
sys	0m0.000s

opt # with fixed http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54349


real	0m0.703s
user	0m0.700s
sys	0m0.000s

nonzero #from PR


real	0m0.826s
user	0m0.820s
sys	0m0.003s

> this email and gcc's __builtin_finite are comparable to the current
> code. Changing the constant as suggested in the PR brings a very
> small but measurable speedup.
> 
Alternative implementations are at
sysdeps/ieee754/dbl-64/wordsize-64/math_private.h 
sysdeps/x86/fpu/bits/mathinline.h
Should we unite them?