[Bug fortran/53509] New: exp and log function give unexpected results when called with numbers as arguments

[Bug fortran/53509] New: exp and log function give unexpected results when called with numbers as arguments

[f.baart at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53509

             Bug #: 53509
           Summary: exp and log function give unexpected results when
                    called with numbers as arguments
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: f.baart@gmail.com


Created attachment 27513
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27513
test script for testing log and exp function

I noticed that the exp and log function in gfortran 4.7.0 and 4.5.3 on OSX
Lion/macports give unexpected results. 

When I call exp(1.0) I get 2.76.. and when I call log(2.71...) I get 1.34... 

$ gfortran-mp-4.7 ./test.f90 && ./a.out
   2.76998615       1.34896958

I tried debugging the program, when in the debugger calling log(2.71..) results
in the correct value. Another way to get the correct answer is to store the
2.71 in a variable and calling log on that. 
I also tried with other real types and they all give different but incorrect
answers. 

Please find attached a test program that reproduces the error on OSX Lion.

Cheers,

Fedor

See also: 
http://trac.macports.org/ticket/34535
http://stackoverflow.com/questions/10673701/can-i-call-the-fortran-log-function-with-a-number

[Bug fortran/53509] exp and log function give unexpected results when called with numbers as arguments

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53509

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |howarth at bromo dot
                   |                            |med.uc.edu

--- Comment #1 from Dominique d'Humieres <dominiq at lps dot ens.fr> 2012-05-28 18:35:15 UTC ---
It works for me on 10.6 (snow leopard). It looks like as a problem with your
GMP/MPFR install. Could you have a look at the GMP bugs to see if there is
nothing related to 10.7 (lion)? CCed Jack Howarth who will know better.

[Bug fortran/53509] exp and log function give unexpected results when called with numbers as arguments

[kargl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53509

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |kargl at gcc dot gnu.org
         Resolution|                            |INVALID

--- Comment #2 from kargl at gcc dot gnu.org 2012-05-28 23:45:18 UTC ---
Not a gfortran problem.  Please, test your MPFR/GMP.

[Bug fortran/53509] exp and log function give unexpected results when called with numbers as arguments

[f.baart at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53509

--- Comment #3 from Fedor Baart <f.baart at gmail dot com> 2012-06-06 17:55:54 UTC ---
Thanks, I managed to solve this by recompiling gmp using gcc 4.5 instead of
clang, which is the default in macports.