[Bug fortran/82207] ieee_class identifies signaling NaNs as quiet NaNs

[sgk at troutmask dot apl.washington.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82207

--- Comment #12 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Wed, Jun 13, 2018 at 03:55:02PM +0000, guez at lmd dot ens.fr wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82207
> 
> --- Comment #11 from Lionel GUEZ <guez at lmd dot ens.fr> ---
> And what about my suggestion that ieee_support_nan(0.) should return false for
> the time being?
> 

AFAIK, the original implementation for the IEEE support followed
either the the F95 Floating-Point Exceptions Tecnical Report (ISO/EIC
TR 15580:2001) or F2003.  These refer to IEC 60599 (1989-01), aka
IEEE 754-1985.  Someone needs to review the entirety of the IEEE
support with respect to the upcoming F2018 standard.  F2018 refers
to ISO/IEC/IEEE 60559:2011.  I know that 60599:2011 is a significant
revision to 60599 (1989-01).  Unfortunately, there are not enough
"someone"s to go around to fix gfortran.

Given a very quick glance at F2003, I think that it may not
be a good idea for ieee_support_nan(0.) to return .false.
as this then means IEEE_IS_NAN(X) cannot be used to determine
if X is a NaN.