Re: strtod ("nan") returns negative NaN

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Aug 14 11:56, Corinna Vinschen wrote:
> On Aug 14 13:45, Masamichi Hosoda wrote:
> > >From a50ee5a4747a99c70469a53fe959f3dc22d3b79a Mon Sep 17 00:00:00 2001
> > From: Masamichi Hosoda <trueroad@trueroad.jp>
> > Date: Tue, 14 Aug 2018 12:50:32 +0900
> > Subject: [PATCH] Fix strtod ("nan") returns qNaN
> > 
> > The definition of qNaN for x86_64 and x86 was wrong.
> > So strtod ("nan") returned sNaN instead of qNaN.
> > 
> > Furthermore, it was inverted the sign bit with the presence of `-` character.
> > So strtod ("-nan") returned qNaN.
> > 
> > This commit fixes definition of qNaN
> > and removes the sign bit inversion when evaluating "nan".
> > ---
> >  newlib/libc/stdlib/gd_qnan.h | 8 ++++----
> >  newlib/libc/stdlib/strtod.c  | 1 +
> >  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> Can you please send this patch to the newlib AT sourceware DOT org
> mailing list?  As soon as something in newlib gets changed, a lot of
> other targets are affected and the guys working on those targets should
> have a chance to chime in.

Looks like strtold is affected as well, just differently:

  printf ("strtod (\"nan\", NULL) = %f\n", strtod ("nan", NULL));
  printf ("strtod (\"-nan\", NULL) = %f\n", strtod ("-nan", NULL));
  printf ("strtold (\"nan\", NULL) = %Lf\n", strtold ("nan", NULL));
  printf ("strtold (\"-nan\", NULL) = %Lf\n", strtold ("-nan", NULL));
  printf ("nan (\"\") = %f\n", nan (""));

==>

  strtod ("nan", NULL) = -nan
  strtod ("-nan", NULL) = nan
  strtold ("nan", NULL) = -nan
  strtold ("-nan", NULL) = -nan
  nan ("") = nan

so it prints always -nan.

With your patch, strtold looks more correct, but it still prints the
sign of NaN:

  strtod ("nan", NULL) = nan
  strtod ("-nan", NULL) = nan
  strtold ("nan", NULL) = nan
  strtold ("-nan", NULL) = -nan
  nan ("") = nan

Question: What's wrong with that?  Wouldn't it be more correct if
strtod returns -NaN for "-nan" as well?


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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