Corinna Vinschen writes:
> 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?
That's iffy, the treatment of sign bits for NaN is quite different from
the usual arithmetic rules. A NaN is literally "not a number", i.e. the
computation has left the domain of representable FP numbers, so it
really doesn't have a sign. That doesn't stop folks from using the sign
bit on its representation, but that's a different story. The sign
properly belong to what is called the "payload", which is usally
ignored. So converting "-nan" (or NaN multiplied by -1) really ought to
be just plain NaN.
Regards,
Achim.
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