[cfp-interest 3433] Re: sign bit of a NaN

[Damian McGuckin]

On Sun, 13 Apr 2025, Jim Thomas wrote:

> The cproj case is interesting because the sign in a non-NAN result 
> depends on the sign bit of a NaN in the input. Thus the sign in the 
> result is unspecified in this case. This could be avoided by requiring 
> the now unspecified sign in the cproj result to be positive in this 
> case. But I don?t think that would be worth breaking existing 
> implementations or the performance hit. I think it would be better to 
> leave the sign unspecified: a natural consequence following from the 
> bit-level definition of copysign.

I agree.

According to some with an interest in low level behaviour, even hardware 
related interest, the Clang behaviour is expected, the GCC behaviour not. 
Interesting. I will solicit some other opinions.

Thanks - Damian