[R-pkg-devel] Modernizing legacy Fortran:, REAL(kind=8)

[Avraham Adler]

Hi, Thomas.

Since all the Fortran code must talk to R through SEXP's written in C,
wouldn't it make sense to use " C_DOUBLE_COMPLEX" and " C_DOUBLE" to ensure
maximum compatibility?

Thanks,

Avi

On Thu, Aug 31, 2023 at 9:42 AM Thomas Petzoldt <
thomas.petzoldt using tu-dresden.de> wrote:

> On 30.08.2023 at 11:58 Ivan Krylov wrote:
> > On Wed, 30 Aug 2023 08:43:04 +0200
> > Thomas Petzoldt <thomas.petzoldt using tu-dresden.de> wrote:
> >
> >> a) change REAL(kind=8) back to DOUBLE PRECISION that is again old
> >> style. It seems to be portable and is still widely used.
> >
> > I don't have a reference as good as the Fortran standard, but Steve
> > Lionel said in Dr. Fortran [*] that DOUBLE PRECISION is still part of
> > the standard fixed-form syntax.
> >
> >>   COMPLEX(KIND=8)
> >
> > This could be particularly problematic if you're trying to interoperate
> > with C, but will probably not surface unless you use LTO:
> > https://bugs.r-project.org/show_bug.cgi?id=18430
> >
> > Unfortunately, there's no standard DOUBLE COMPLEX.
> >
>
> Thank you, this helps. I had a look in Dr. Fortran myself and some other
> sites, but especially the COMPLEX definitions remain unclear.
>
> I tried now the following, because the included original Fortran codes
> follow slightly different standards:
>
> - replace COMPLEX(KIND=8) with DOUBLE COMPLEX in source files that use
> DOUBLE PRECISION otherwise
>
> - replace real(kind=8) with real(kind=kind(0.0d0)) in the more modern
> source files
>
> This is pragmatic and may not be the best way, but looks mostly
> consistent. Now I checked the package and everything was ok, but I was
> not able reproduce the warnings from the previous version.
>
> I assume that I have to set an environment variable to see the warnings,
> but which one?
>
> I use gfortran/gcc 13.2.1-1 on Fedora 38.
>
> Thanks!
>
> Thomas
>
> --
> https://tu-dresden.de/Members/thomas.petzoldt
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