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(g77-295.info)Floating-point Exception Handling

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Floating-point Exception Handling
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   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
an x86-based GNU system:

     #include <fpu_control.h>
     static void __attribute__ ((constructor))
     trapfpe ()
     {
       fpu_control_t cw =
         _FPU_DEFAULT &
         ~(_FPU_MASK_IM | _FPU_MASK_ZM | _FPU_MASK_OM);
       _FPU_SETCW(cw);
     }

   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.