On Aug 14 21:17, Masamichi Hosoda wrote:
> > 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 <truer...@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(-)
> >> [...]
> > 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?
>
> In my investigate,
> strtold sets sign bit when parameter has '-' character.
> The wrong long double NaN definition is negative NaN that is set sign bit.
> So without my patch, both strtold ("nan") and
> strtold ("-nan") return negative NaN.
>
> On the other hand, strtod inverts the sign when parameter has '-' character.
> The wrong double NaN definition is negative NaN.
> So without my patch, strtod ("nan") returns negative NaN
> and strtod ("-nan") returns positive NaN.
Your patch improves the situation, that's a sure thing and I did not
question that.
I just wonder why returning -NaN when the input is "-nan" isn't the
better approach. After all:
printf ("nan (\"\") = %f\n", nan (""));
printf ("-nan (\"\") = %f\n", -nan (""));
==>
nan ("") = nan
-nan ("") = -nan
So, shouldn't the ideal outcome be this:
strtod ("nan", NULL) = nan
strtod ("-nan", NULL) = -nan
strtold ("nan", NULL) = nan
strtold ("-nan", NULL) = -nan
?
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
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