Using and Porting GNU Fortran
15.3.29 Floating-point Exception Handling
The gcc backend and, consequently, g77, currently provides no
general control over whether or not floating-point exceptions are trapped or
ignored.
(Ignoring them typically results in NaN values being
propagated in systems that conform to IEEE 754.)
The behaviour is normally inherited from the system-dependent startup
code, though some targets, such as the Alpha, have code generation
options which change the behaviour.
Most systems provide some C-callable mechanism to change this; this can
be invoked at startup using gcc's constructor attribute.
For example, just compiling and linking the following C code with your
program will turn on exception trapping for the "common" exceptions
on a GNU system using glibc 2.2 or newer:
| | #define _GNU_SOURCE 1
#include <fenv.h>
static void __attribute__ ((constructor))
trapfpe ()
{
/* Enable some exceptions. At startup all exceptions are masked. */
feenableexcept (FE_INVALID|FE_DIVBYZERO|FE_OVERFLOW);
}
|
A convenient trick is to compile this something like:
| | gcc -o libtrapfpe.a trapfpe.c
|
and then use it by adding `-trapfpe' to the g77 command line
when linking.
