[cfp-interest 3712] Re: [SC22WG14.34253] Sign of zero from fromfp functions

[Jim Thomas]

ISO/IEC 60559 requires its conversion operations that correspond to the C fromfp functions to preserve the sign of numeric input. The Annex F binding and deference to ISO/IEC 60559 implicitly give the fromfp functions the same specification. CFP will look into making this specification explicit.

- Jim Thomas

> On Nov 7, 2025, at 11:30 AM, Joseph Myers <josmyers at redhat.com> wrote:
> 
> Do the fromfp functions follow the same rules about the sign of a zero 
> result as all the other functions rounding to an integer in a floating 
> type (i.e., the sign of a zero result is the sign of the floating 
> argument)?  In particular, is it correct that the ufromfp functions return 
> -0 when a negative argument rounds to 0?  The issue of the sign of a zero 
> result was introduced when we changed these functions to return a floating 
> type for C23 (N2548), but we didn't add any text to the standard 
> discussing it for these functions.
> 
> -- 
> Joseph S. Myers
> josmyers at redhat.com
>