Re: [PATCH 1/4] alpha: fix ceil on sNaN input [committed/2.23]

[Richard Henderson <rth at twiddle dot net>]

On 12/08/2016 08:11 PM, Mike Frysinger wrote:
> On 08 Dec 2016 20:01, Richard Henderson wrote:
> > On 12/08/2016 10:51 AM, Mike Frysinger wrote:
> > >  __ceil (double x)
> > >  {
> > > +  if (isnan (x))
> > > +    return x + x;
> > > +
> > >    if (isless (fabs (x), 9007199254740992.0))	/* 1 << DBL_MANT_DIG */
> > >      {
> > >        double tmp1, new_x;
> >
> > Probably better to test for nan in the else of this if, since the isless is
> > surely more likely than the nan.
> >
> > That goes for all of the changes.
>
> i guess fabs(NaN) and isless(NaN, ...) isn't a problem ?

No, that's fine.

> would it be equiv to do ?
> 	if (__glibc_unlikely (isnan (x)))

No, since that test would still happen first.  I think that

  if (isless(...))
    ...
  else if (isnan(x))
    return x + x;

is better for the average case.


r~