Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!bu.edu!inmet!mazur
From: mazur@inmet.inmet.com
Newsgroups: comp.lang.c
Subject: Re: Execution time bottleneck: How
Message-ID: <20900015@inmet>
Date: 15 Feb 91 19:51:00 GMT
References: <233522@<1991Feb12>
Lines: 23
Nf-ID: #R:<1991Feb12:233522:inmet:20900015:000:920
Nf-From: inmet.inmet.com!mazur    Feb 15 14:51:00 1991


In article <21658@yunexus.YorkU.CA> racine@yunexus.yorku.ca (Jeff Racine) writes:
>   for (j=1; j <= n; j++) {
>      sum = 0.0;
>      for (i=1; i<= n; i++) {
>         sum += exp( con * (x[i]-x[j]) * (x[i]-x[j]) );
>      }
>      a[j] = k*sum;
>   }
>This part of the algorithmn is a bottleneck. I want to make this as
>quick as possible. What are my options? I have heard that assembler
>would be faster. How much faster would assembler be? Would it be worth
>the effort? Are there other alternatives that you can see?

I missed the original article, so I'm not sure what you are compiling this
code with, but rewriting the loop so that you decrement from (n-1) to 0 
may reduce the number of instructions necessary to do the comparison (i.e.,
you may be able to do a "tst; beq" instead of "ld i, tst, beq").  Small
savings, but they add up.

Beth Mazur               
mazur@inmet.inmet.com  
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