[Bug fortran/82143] add a -fdefault-real-16 flag

["kargl at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82143

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
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                 CC|                            |kargl at gcc dot gnu.org

--- Comment #2 from kargl at gcc dot gnu.org ---
(In reply to janus from comment #0)
> gfortran currently knows the options -fdefault-real-8 and -fdefault-double-8.
> 
> It would be useful to add an -fdefault-real-16 (corresponding to ifort's
> -real-size 128) and maybe also -fdefault-double-16.
> 
> For completeness, also -fdefault-real-4 might be worth adding (which would
> correspond to the current default behavior).

Actaully, the -fdefault-real* and -fdefault-integer-* options
should be deprecated.  These options are broken by design, and
probably do not do what one wants.  Use the -freal-4-real-16
(and similar options).

% cat cat a.f90 
program foo
   real x
   x = 1. / 3.
   print *, x
end program foo
%  gfortran6 -static -o z a.f90 && ./z
  0.333333343    
% gfortran6 -static -o z -freal-4-real-16 a.f90 && ./z
  0.333333333333333333333333333333333317