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From: news@caen.engin.umich.edu (news)
Newsgroups: comp.sys.apollo
Subject: trapping of arithmetic exceptions
Keywords: f77, cc, overflow/underflow
Message-ID: <47d29220.bb89@spam.engin.umich.edu>
Date: 3 Jan 90 05:00:00 GMT
Distribution: usa
Organization: U of M Engineering, Ann Arbor, Mich.
Lines: 39

In order to test some linpack routines (Fortran) I need to do some
trapping  of arithmetic execptions . Some of the test programs
operate near underflow/overflow boundaries.
So I wrote a routine in C to do the trapping. I include below the headers of
such a routine  ( a test program I have is 272 lines long if someone is
interested):

traps(i1max,i3max,i5max,i2max,i4max)
int  i1max,i2max,i3max,i4max,i5max;  
/*
     This routine sets the number of arithmetic exceptions permitted.

     i1max  is the number of fixed    point overflows      permitted.
     i2max  is the number of fixed    point divide by zero permitted.
     i3max  is the number of floating point overflows      permitted.
     i4max  is the number of floating point divide by zero permitted.
     i5max  is the number of floating point underflows     permitted.
*/                                                   
{
      signal(SIGFPE,handler); 
}

I've only been able to trap integer and floating division by zero.
Overflows and underflows are not caught at all (they return +Inf or -Inf or
just the biggest number you can have). This is not peculiar to the apollos.
I noticed a similar behavior on the suns, decs and alliant.  I believe I read
somewhere this is what f77 following IEEE rules is supposed to do (I don't like it).
                                        
We are running SR10.1 (similar behavior in 10.2) BSD4.3.

My question: is it possible to trap (either in C or f77) overflows/underflows  and
redirect control to a handler program ?
A example would be most welcome. Or if you already wrote such a trapping when
testing the linpack demos, I would appreciate getting a copy of it.

   Roque D. Oliveira
   oliveria@caen.engin.umich.edu
   Computer Aided Engineering Network
   U. of Michigan