Re: optimization/520: exp function can't handle -inf in optimized mode on i686

["Tim Prince" <tprince at computer dot org>]

The following reply was made to PR optimization/520; it has been noted by GNATS.

From: "Tim Prince" <tprince@computer.org>
To: <karsten.trulsen@math.sintef.no>, <gcc-gnats@gcc.gnu.org>
Cc: <karsten.trulsen@math.sintef.no>
Subject: Re: optimization/520: exp function can't handle -inf in optimized mode on i686
Date: Mon, 11 Sep 2000 05:02:19 -0700

 Yes,.  I still fail to understand why the additional code to fix this is not
 acceptable, when no one has even shown any benchmarks to show a significant
 loss of performance.  But that is a matter for glibc, not part of gcc.
 ----- Original Message -----
 From: <karsten.trulsen@math.sintef.no>
 To: <gcc-gnats@gcc.gnu.org>
 Cc: <karsten.trulsen@math.sintef.no>
 Sent: Monday, September 11, 2000 12:28 AM
 Subject: optimization/520: exp function can't handle -inf in optimized mode
 on i686
 
 
 >
 > >Number:         520
 > >Category:       optimization
 > >Synopsis:       exp function can't handle -inf in optimized mode on i686
 > >Confidential:   no
 > >Severity:       serious
 > >Priority:       medium
 > >Responsible:    unassigned
 > >State:          open
 > >Class:          sw-bug
 > >Submitter-Id:   net
 > >Arrival-Date:   Mon Sep 11 00:36:00 PDT 2000
 > >Closed-Date:
 > >Last-Modified:
 > >Originator:     Karsten Trulsen
 > >Release:        gcc-2.95.2
 > >Organization:
 > >Environment:
 > i686 RedHat 6.2
 > >Description:
 > exp(-inf) should return 0.  However, when compiled with
 > optimization turned on, on a i686 (running RedHat 6.2),
 > the return value is "nan".
 > >How-To-Repeat:
 > #include <math.h>
 > #include <stdio.h>
 >
 > int
 > main (void)
 > {
 >   double x = 0;
 >   printf ("%g\n", x);
 >   x = log (x);
 >   printf ("%g\n", x);
 >   x = exp (x);
 >   printf ("%g\n", x);
 >   return 1;
 > }
 > >Fix:
 > The error is probably in the assembly code in the file
 > /usr/include/bits/mathinlines.h.
 > >Release-Note:
 > >Audit-Trail:
 > >Unformatted: