Built-in testing for signaling nan?

[Ian Lance Taylor]

On Wed, Nov 6, 2013 at 5:44 AM, FX <fxcoudert@gmail.com> wrote:
>
> GCC has a number of floating-point-related type-generic built-ins, which are great and which we largely rely on in the gfortran runtime library (rather than depending on the possibly poor-quality target math library).
>
> However, I have not been able to find a way to test for a signaling NaN using the existing built-ins? __builtin_fpclassify() and __builtin_isnan() both return the same thing for quite and signaling NaNs. We have a __builtin_nans() function to generate a signaling NaN, but nothing to find one.
>
> Am I missing something? Would it be hard to implement such a built-in?

Given how murky signaling NaNs are in practice, I think it's worth
asking: why do you want to know?

Ian