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Re: strtod ("nan") returns negative NaN




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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