Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 5/3/83; site noao.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!princeton!astrovax!noao!allan
From: allan@noao.UUCP
Newsgroups: net.physics
Subject: Re: VMS vs. Unix (programs)
Message-ID: <361@noao.UUCP>
Date: Wed, 27-Jun-84 14:23:24 EDT
Article-I.D.: noao.361
Posted: Wed Jun 27 14:23:24 1984
Date-Received: Thu, 28-Jun-84 06:34:08 EDT
References: <590@sdcsla.UUCP>
Organization: Natl. Optical Astronomy Obs.  Tucson AZ USA
Lines: 23

A little extra information on the timing of my matrix multiplication program.
Following a suggestion (I'm afraid I forget from whom), I changed the 
declaration of the loop counters to be register int's. This speeded things
up from 64 seconds to 53 seconds; a fair gain. I was a bit surprised and 
very pleased to see how much improvement the declaration

register float *pa, *pb, *pc;
 
and the use of pointer incrementing does for the timing. Of course, like most
things, it is obvious with hindsight. Much of the time of the original 
program is spent in calculating the addresses of the array elements.
I cannot think of a way of forcing fortran to do this incrementing in the
'obviously sensible' way, although as you point out, a good optimiser should
do it for you.

I conceed. C is faster than fortran when you write your programs correctly.


Peter Allan
Kitt Peak National Observatory
Tucson, Az
UUCP:	{akgua,allegra,arizona,decvax,hao,ihnp4,lbl-csam,seismo}!noao!allan
ARPA:	noao!allan@lbl-csam.arpa