Re: [PATCH] PR70117, ppc long double isinf

[Alan Modra <amodra at gmail dot com>]

On Wed, Apr 06, 2016 at 10:46:48AM +0200, Richard Biener wrote:
> On Wed, Apr 6, 2016 at 10:31 AM, Alan Modra <amodra@gmail.com> wrote:
> > On Tue, Apr 05, 2016 at 11:29:30AM +0200, Richard Biener wrote:
> >> In general the patch looks like a good approach to me but can we
> >> hide that
> >>
> >> > +  const struct real_format *fmt = FLOAT_MODE_FORMAT (mode);
> >> > +  bool is_ibm_extended = fmt->pnan < fmt->p;
> >>
> >> in a function somewhere in real.[ch]?
> >
> > On looking in real.h, I see there is already a macro to do it.
> >
> > Here's the revised version that properly tests the long double
> > subnormal limit.  Bootstrapped and regression tested
> > powerpc64le-linux.
> 
> Can you add a testcase or two for the isnormal () case?

Sure.  I'll adapt the testcase I was using to verify the output,
attached in case you're interested.

> I wonder whether the isnormal tests are too excessive to put in
> inline code and thus libgcc code wouldn't be better to handle this...

Out-of-line would be better for -Os at least.

> At least the glibc implementation looks a lot simpler to me ...
> (if ./sysdeps/ieee754/ldbl-128ibm/s_fpclassifyl.c is the correct one).

It looks more or less the same to me, except done by bit twiddling on
integers.  :)

> Thus an alternative is to inline sth similar via the folding or via
> an optab and not folding (I'd prefer the latter).
> 
> That said, did you inspect the generated code for a isnormal (x)
> call for non-constant x?

Yes, I spent quite a bit of time fiddling trying to get optimal code.
I'm not claiming I succeeded..

>  What does XLC do here?

Not sure, sorry.  I don't have xlc handy.  Will try later.

-- 
Alan Modra
Australia Development Lab, IBM

int __attribute__ ((noclone, noinline))
isnormal (double x)
{
  return __builtin_isnormal (x);
}

int __attribute__ ((noclone, noinline))
isnormal_ld (long double x)
{
  return __builtin_isnormal (x);
}

double min_norm = 0x1p-1022;
double min_denorm = 0x1p-1074;
double ld_low = 0x1p-969;

int
main (void)
{
  static union { long double ld; unsigned long l[2]; } x;

  __builtin_printf ("%a %d\n", min_norm, isnormal (min_norm));
  __builtin_printf ("%a %d\n", min_norm * 0.5, isnormal (min_norm * 0.5));

  x.ld = ld_low;
  __builtin_printf ("%La (%016lx %016lx) %d\n", x.ld, x.l[0], x.l[1],
		    isnormal_ld (x.ld));
  x.ld = -ld_low;
  __builtin_printf ("%La (%016lx %016lx) %d\n", x.ld, x.l[0], x.l[1],
		    isnormal_ld (x.ld));
  x.ld = -min_norm * 0.5;
  x.ld += ld_low;
  __builtin_printf ("%La (%016lx %016lx) %d\n", x.ld, x.l[0], x.l[1],
		    isnormal_ld (x.ld));
  x.ld = min_norm * 0.5;
  x.ld -= ld_low;
  __builtin_printf ("%La (%016lx %016lx) %d\n", x.ld, x.l[0], x.l[1],
		    isnormal_ld (x.ld));
  x.ld = -min_norm;
  x.ld += ld_low;
  __builtin_printf ("%La (%016lx %016lx) %d\n", x.ld, x.l[0], x.l[1],
		    isnormal_ld (x.ld));
  x.ld = min_norm;
  x.ld -= ld_low;
  __builtin_printf ("%La (%016lx %016lx) %d\n", x.ld, x.l[0], x.l[1],
		    isnormal_ld (x.ld));
  x.ld = -min_denorm;
  x.ld += ld_low;
  __builtin_printf ("%La (%016lx %016lx) %d\n", x.ld, x.l[0], x.l[1],
		    isnormal_ld (x.ld));
  x.ld = min_denorm;
  x.ld -= ld_low;
  __builtin_printf ("%La (%016lx %016lx) %d\n", x.ld, x.l[0], x.l[1],
		    isnormal_ld (x.ld));
  x.ld = min_denorm;
  x.ld += ld_low;
  __builtin_printf ("%La (%016lx %016lx) %d\n", x.ld, x.l[0], x.l[1],
		    isnormal_ld (x.ld));
  x.ld = -min_denorm;
  x.ld -= ld_low;
  __builtin_printf ("%La (%016lx %016lx) %d\n", x.ld, x.l[0], x.l[1],
		    isnormal_ld (x.ld));
  return 0;
}