Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!zaphod.mps.ohio-state.edu!rpi!batcomputer!finn
From: finn@batcomputer.tn.cornell.edu (Lee Samuel Finn)
Newsgroups: comp.sys.next
Subject: 68040 Math / Why so much system time?
Summary: 68040 trancendental math uses exorbitant system time
Keywords: 68040 math, system time
Message-ID: <1991Feb14.160749.19048@batcomputer.tn.cornell.edu>
Date: 14 Feb 91 16:07:49 GMT
Sender: lsf@astrosun.tn.cornell.edu
Distribution: na
Organization: Cornell Theory Center
Lines: 55

Ok, I've just finished upgrading to OS2.0 and the 68040 logic board.
Recalling some discussion earlier, which was never resolved on the
net, I wrote a stupid program to exercise some trancendental
arithmetic and then timed the puppy:

#include <math.h>
#define n 10000
#define m 100
#define pi 3.141592653589  
void test2(double *a){ return; }

main(){
    int i,j;
    double b,a[n];
    
    for(j=0;j<m;j++) {
	for(i=0;i<n;i++) a[i]=sin(i*pi/n);
	test2(a);
    }	
    return 0;
}	
	
    
The results are astonishing:

% cc -O testc.c -o testc -lm
% time testc
4.8u 27.7s 0:38 84% 0+0k 3+0io 0pf+0w

Nearly 86% of the execution time of this program is system, and only
14% is user. If the call to sin() is changed to sqrt(), the statistics
are _very_ different:

% cc -O testc.c -o testc -lm
% time testc
9.0u 0.0s 0:09 99% 0+0k 1+0io 0pf+0w

Now, all the execution time is user time.

Why all the system time spent doing a sin()? Just fyi, the same prog
(with call to sin()) on a Sun sparc 1+ runs 16.1 sec in user time ---
a factor of 2 faster, but with a call to sqrt() runs 23.7 sec in user
time: a factor of 3 _slower_. Just what is going on in doing
trancendental functions on the 68040?

Please reply directly to me, as I am splitting tomorrow morning and
won't be able to see news for about a week. 

Thanks,

lsf@astrosun.tn.cornell.edu

P.S. If this or a similar posting has been seen in the last 24 hours,
apologises; I tried posting once before and got a bunch of errors that
suggested we were out of space to post messages so I'm tring again now.