Re: [PATCH, Fortran] Revert to non-multilib-specific ISO_Fortran_binding.h

[Jakub Jelinek <jakub@redhat.com>]

On Mon, Sep 13, 2021 at 07:07:01PM +0200, Tobias Burnus wrote:
> Regarding FreeBSD: Does this output different values? – If yes, we know
> what to do, otherwise – hmm.
> 
> [...]
> 
> > > Wouldn't it be better to use the __LDBL_* macros anyway and not rely on
> > > float.h?  The header doesn't want to test what float.h tells about the
> > > long double type, but what the compiler knows about it.
> > I originally wrote the code to use the internal GCC __LDBL_* macros as
> > you suggest, but Tobias complained that then the gfortran-provided .h
> > file could not be used to compile the C parts of the program with some
> > other C compiler.
> For instance, clang does not seem to provide those - and in some cases,
> it can be useful to mix gfortran code with code complied by other
> compilers (icc, clang, ...).
> > Maybe it needs to first check the internal macros and then look for
> > the float.h versions if it can't find them?
> 
> I think that makes sense. (Adding a comment that #include <float.h> is
> for non-GCC compilers, only.)

At least according to godbolt and my tests, both clang and icc predefine
those macros too.  But there are other C compilers, sure.

So we'd need #if defined (__LDBL_MAX__) && defined (__LDBL_*_) // whatever
we need
#else
#include <float.h>
...
#endif
or so.

	Jakub