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Date: Tue, 14 Aug 2018 10:12:34 -0700 (PDT)
From: Steven Penny <svnpenn AT gmail DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: strtod ("nan") returns negative NaN
References: <20180814132301 DOT GX3747 AT calimero DOT vinschen DOT de>
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On Tue, 14 Aug 2018 15:23:01, Corinna Vinschen wrote:
> I just wonder why returning -NaN when the input is "-nan" isn't the
> better approach.  After all:
>
>   printf ("nan (\"\") =3D %f\n", nan (""));
>   printf ("-nan (\"\") =3D %f\n", -nan (""));
>
> =3D=3D>
>
>   nan ("") =3D nan
>   -nan ("") =3D -nan
>
> So, shouldn't the ideal outcome be this:
>
>   strtod ("nan", NULL) =3D nan
>   strtod ("-nan", NULL) =3D -nan
>   strtold ("nan", NULL) =3D nan
>   strtold ("-nan", NULL) =3D -nan

a number can be positive or negative. as "NaN" is by definition not a number,
it cannot be positive or negative, it is simply itself, something anathema to
a number.

The only case where "-nan" would be acceptable is the string case, but even in
that instance it is still not negative, it is merely a string that happens to
start with "hyphen-minus" U+002D, and has no bearing on a sign, just as a string
can have no sign.


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