[YLUG] Why is this so much faster on an Opteron?

[Roger Leigh]

"Robert Hulme" <rob at robhulme.com> writes:

> I have this code:
>
> #include <stdio.h>
>
> int main(char **argv,int argc) {
>  double f=0;
>  int i=0;
>  int j=0;
>  int c=1;
>  for(i=0;i<10000;i++)
>  for(j=0;j<10000;j++,c++)
>    f=f+0.505/(j+i/(1.0+j+i));
>  return (int)f%10;
> }

What's the point of c?

> If I compile it with -O2 it takes about 40 seconds to run on my
> Pentium D (dual core pentium 4) desktop, but only about 2 seconds
> (when using time) to run on a 2.2Ghz Opteron.
>
> How long does it take to run on peoples machines?

% gcc-4.2 -O2 -o test test.c
% time ./test
./test  8.18s user 0.00s system 94% cpu 8.675 total

% cat /proc/cpuinfo
processor       : 0
cpu             : 7447A, altivec supported
clock           : 1416.666661MHz
revision        : 0.2 (pvr 8003 0102)
bogomips        : 83.20
timebase        : 41620997
platform        : PowerMac
machine         : PowerMac10,1
motherboard     : PowerMac10,1 MacRISC3 Power Macintosh
detected as     : 287 (Mac mini)
pmac flags      : 00000010
L2 cache        : 512K unified
pmac-generation : NewWorld


Regards,
Roger

-- 
  .''`.  Roger Leigh
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