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From: "sgk at troutmask dot apl.washington.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/113152] Fortran 2023 half-cycle trigonometric functions
Date: Mon, 22 Jan 2024 18:06:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113152

--- Comment #17 from Steve Kargl <sgk at troutmask dot apl.washington.edu> =
---
On Mon, Jan 22, 2024 at 05:35:41PM +0000, anlauf at gcc dot gnu.org wrote:
> --- Comment #16 from anlauf at gcc dot gnu.org ---
> (In reply to Steve Kargl from comment #14)
> > On Sun, Jan 21, 2024 at 09:52:39PM +0000, anlauf at gcc dot gnu.org wro=
te:
> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113152
> > >=20
> > > I think that you cannot do
> > >=20
> > > +  if (MPFR_HALF_CYCLE)
> > >=20
> > > you really must use
> > >=20
> > > #if MPFR_HALF_CYCLE
> > >=20
> >=20
> > #include <stdio.h>
> > #include "mpfr.h"
> >=20
> > #define MPFR_HALF_CYCLE (MPFR_VERSION_MAJOR * 100 + MPFR_VERSION_MINOR =
>=3D
> > 402)
> >=20
> > int
> > main(void)
> > {
> >    if (MPFR_HALF_CYCLE)
> >       printf("here\n");
> >    else
> >       printf("there\n");
> >    return (0);
> > }
> >=20
> > % cc -o z -I/usr/local/include a.c && ./z
>=20
> This does not test the right thing.
>=20
> % cat sgk.cc
> #include <stdio.h>
>=20
> #define MPFR_HALF_CYCLE 0

This is not what the pre-processor should be doing
(on at least FreeBSD).  See below.


> int
> main(void)
> {
>    if (MPFR_HALF_CYCLE)
>       printf_not_declared_if_0 ("here\n");
>    else
>       printf ("there\n");
>    return (0);
> }
>=20
> % g++ sgk.cc
> sgk.cc: In function 'int main()':
> sgk.cc:9:7: error: 'printf_not_declared_if_0' was not declared in this sc=
ope
>        printf_not_declared_if_0 ("here\n");
>        ^~~~~~~~~~~~~~~~~~~~~~~~

Of course, it will fail.  You need to actually have a
printf_not_declared_if_0 function defined during parsing.

#include <stdlib.h>
#include <stdio.h>

#define MPFR_HALF_CYCLE 1
#define printf_not_declared_if_0(a) abort()

int
main(void)
{
   if (MPFR_HALF_CYCLE)
      printf_not_declared_if_0 ("here\n");
   else
      printf ("there\n");
   return (0);
}

~/work/x/bin/g++ -I/usr/local/include -o z a.cc && ./z
Abort (core dumped)

Changing 1 to 0 the MPFR_HALF_CYCLE define.

 ~/work/x/bin/g++ -I/usr/local/include -o z a.cc && ./z
there

Going back to my original example and g++ from master, I'm seeing

% ~/work/x/bin/g++ -I/usr/local/include -E a.cc

int
main(void)
{
   if ((
# 9 "a.cc" 3
      4=20
# 9 "a.cc"
      * 100 +=20
# 9 "a.cc" 3
      2=20
# 9 "a.cc"
      >=3D 402))
      printf("here\n");
   else
      printf("there\n");
   return (0);
}

and with clang++

% c++ -E -I/usr/local/include a.cc
int
main(void)
{
   if ((4 * 100 + 2 >=3D 402))
      printf("here\n");
   else
      printf("there\n");
   return (0);
}

Is there something that is different between your OS and FreeBSD?
Or is there some fundamental difference between C and C++ that
I am unaware of?=