Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!sdr.slb.com!SAITO
From: SAITO@sdr.slb.com ("Naoki Saito  Ext. 5471", GEO-002)
Newsgroups: gnu.gcc
Subject: slow math computation in gcc-1.34
Message-ID: <8906011741.AA09171@AENEAS.MIT.EDU>
Date: 1 Jun 89 16:26:00 GMT
Sender: daemon@tut.cis.ohio-state.edu
Distribution: gnu
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	Hello, folks!  I installed gcc-1.34 on the Sun3 OS 4.0.1 system.
I tried a simple math program and compared with Sun's C compiler.  gcc was
beaten by Sun's C in this case.  I heard gcc-1.35 has inline functions for
math library, but is there any way to improve the math computation speed
without installing gcc-1.35?  The following is the example and results.

======================================================================
/* mathtest2.c

#include <stdio.h>
#include <math.h>

main()
{
  int i;
  double x, y;

  for (i = 0; i < 10000; i++)
    {
      x = (double)i;
      y = log(exp(x));
    }
}
===========================================================================
$ gcc -O -m68881 -o mathtest2.gcc mathtest2.c -lm
$ cc -O -f68881 -o mathtest2.cc mathtest2.c -lm
$ cc -O -f68881 -o mathtest2.cc.il mathtest2.c /usr/lib/f68881/libm.il

$ /bin/time mathtest2.gcc
        4.3 real         4.0 user         0.0 sys  
$ /bin/time mathtest2.cc
        2.6 real         2.4 user         0.0 sys  
$ /bin/time mathtest2.cc.il 
        0.7 real         0.5 user         0.1 sys  

I would appreciate your advise!

Naoki Saito (saito@sdr.slb.com)
Schlumberger-Doll Research