Re: std::numeric_limits<__float128>::signaling_NaN + __float128-Type

From: John Maddock (jz.maddock_at_[hidden])
Date: 2022-02-11 18:24:22

On 10/02/2022 22:18, Gero Peterhoff via Boost wrote:
> Am 10.02.22 um 14:07 schrieb John Maddock via Boost:
>> On 07/02/2022 19:18, Gero Peterhoff via Boost wrote:
>>> Hello,
>>> please see https://godbolt.org/z/Ksshxvhaj
>>>
>>> 1) std::numeric_limits<__float128>::signaling_NaN always returns 0 but gcc-__builtin_nansq doesn't. I think __builtin_nansq is correct as it is also distinct from std::numeric_limits<__float128>::quiet_NaN (__builtin_nanq).
>> Can you submit a PR please?  We would probably need to check for the presence of the intrinsic with __has_intrinsic as I don't *think* it's always been available?
> Hi John,
> I can't think of anything besides the sledgehammer method (cast) either, assuming the value of gcc __builtin_nansq is universal.

I'm not sure it's actually supported at all, I see:

undefined reference to `nansq'

whenever I try to use the builtin, the function nansq appears not to 
currently exist at all in libquadmath, and isn't declared in current 
quadmath.h.  A quick google yields no hits as well.

I wonder if this is still work in progress for gcc?

Does anyone have a (non-theoretical) use case for signalling 
quad-precision NaN's?  And or a working test case?

Thanks, John.

-- 
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus