[PATCH] libm,ieee754:New algorithm of fmod function for, dbl-64/wordsize-64

[Joseph Myers]

On Fri, 20 Nov 2020, Kirill Okhotnikov via Libc-alpha wrote:

> > > + * Performance:
> > > + *   Various tests on AArch64 and x86_64 shows that the current algorithm
> > > is faster than the previous one by factor 1.5-10 depend
> > > + *   on input.
> > I think performance information belongs in the proposed commit message,
> > not in comments in the code which should describe the code as it is in a
> > self-contained way rather than referring to a previous version.
> Sorry. I did not get the idea.

I don't think comments in the code should refer to the previous algorithm; 
I think they should only relate to the version of the code containing 
those comments.

Comparisons of performance of the two versions are fully appropriate in 
the commit message, however.

> > > +  sx.value *= one;  /* Optimized out? May be math_check_force_underflow?
> > > */
> > math_check_force_underflow would be incorrect here.  We don't try to
> > ensure exact underflow exceptions (the case where IEEE signals
> > FE_UNDERFLOW without FE_INEXACT and default exception handling does not
> > raise the corresponding flag).  fmod always produces exact results
> > ("invalid" is the only exception it can raise the flag for, for x infinite
> > or y zero if the other is not a NaN, or if either argument is a signaling
> > NaN).
> > 
> I just get it from previous code. Such thing was also questionable for me.
> Fully remove it?

Yes, I think remove it.

-- 
Joseph S. Myers
joseph@codesourcery.com