[Bug fortran/41831] New: Bug with management of NaNs

["michael dot baudin at scilab dot org" <gcc-bugzilla at gcc dot gnu dot org>]

I find that there is a bug with respect to the 
management of the NaNs from C to fortran.
This bug happens on Ubuntu 64bits (and not with 32bits).

returnanan.c defines 2 functions
nan = returnanan() : returns a NAN, 
void returnanan2(nan) : sets the NAN in the input argument, passed by address.

test.f computes NAN with 3 methods :
#1 : uses returnanan()
#2 : creates NAN with (1-ONE)/(1-ONE)
#3 : uses returnanan2(nan)

This produces the following output :

(returnanan) nan = nan               // OK
 X #1:   0.0000000000000000          // WRONG
 X #2:                       NaN     // OK
(returnanan2) nan = nan              // OK
 X #3:                       NaN     // OK

My conclusion is that there is a problem when the 
NAN is passed from the C to the fortran.
I cannot explain the fact that if the address of the 
NAN is passed to the C function, it works.

This bug is related to Scilab, see :
http://bugzilla.scilab.org/show_bug.cgi?id=4378

Best regards,

Michaël Baudin

--

Software Development Engineer
michael.baudin@scilab.org
The Scilab Consortium
http://www.scilab.org/

=======================================
returnanan.c:
#define C2F(name) name##_
#include <stdio.h>
double C2F(returnanan)(void)
{
        static int first = 1;
        static double nan = 1.0;

        if ( first )
        {
                nan = (nan - (double) first)/(nan - (double) first);
                first = 0;
        }
        printf ( "(returnanan) nan = %e\n",nan);
        return ((double)nan);
}
void C2F(returnanan2)(double * nan)
{
        double one = 1.0;
        *nan = (1.0 - one)/(1.0 - one);
        printf ( "(returnanan2) nan = %e\n",*nan);
}
=======================================
test.f
      PROGRAM test
      DATA ONE/1.0D0/
      DOUBLE PRECISION X
      X = returnanan()
      PRINT * , "X #1:", X
      X = (1-ONE)/(1-ONE)
      PRINT * , "X #2:", X
      call returnanan2(X)
      PRINT * , "X #3:", X
      END    
=======================================
Now type :
gcc -c returnanan.c
gfortran -c test.f
gfortran -o mytest returnanan.o test.o
./mytest

=======================================
$ gcc -v
Utilisation des specs internes.
Target: x86_64-linux-gnu
Configuré avec: ../src/configure -v --with-pkgversion='Ubuntu 4.3.3-5ubuntu4'
--with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.3
--program-suffix=-4.3 --enable-clocale=gnu --enable-libstdcxx-debug
--enable-objc-gc --enable-mpfr --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Modèle de thread: posix
gcc version 4.3.3 (Ubuntu 4.3.3-5ubuntu4)


-- 
           Summary: Bug with management of NaNs
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: michael dot baudin at scilab dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41831