Execution time bottleneck: How

[mazur at inmet.inmet.com]

In article <21658 at yunexus.YorkU.CA> racine at 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 at inmet.inmet.com  
-..!uunet!inmet!mazur