[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: unassig...@gcc.gnu.org
ReportedBy: f.ba...@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

[f.baart at gmail dot com]

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

--- Comment #3 from Fedor Baart  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.