Re: [PATCH 5/6] x86-64: Add pow/powf to libmvec microbenchmark

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The 11/10/2021 19:31, Sunil Pandey via Libc-alpha wrote:
> On Wed, Nov 10, 2021 at 12:27 PM Joseph Myers <joseph@codesourcery.com>
> wrote:
> 
> > On Tue, 9 Nov 2021, Sunil K Pandey via Libc-alpha wrote:
> >
> > > +# Random inputs in [a=0.01,b=100.00], [c=0.01,d=10.00]
> >
> > I think there should be a reasonable proportion of negative exponents,
> > unless you have evidence that negative exponents are rarely used in
> > practice.  (The *first* argument of pow being negative is of use (produces
> > finite results) in much more limited cases, so may well be much rarer.)
> >
> 
> Negative exponents not used in the input file to avoid denormal
> processing. Negative
> exponent
> may hit the underflow domain when pow(x, -y) produces denormals as results
> or as intermediate
>  values. Both going to touch very slow special pow() path and invokes Intel
> software assist for
> denormals processing. All of this will distort the overall performance
> result of the main path.
> Also the base argument should be small so that it doesn’t produce denormals.

i'd expect typical negative exponents would not
cause subormal computations.

does powf(100, -10) have intermediate underflow
with the x86 libmvec code?