Template-ing a 'for' loop in C++?

Question

I have a C++ snippet below with a run-time for loop,

for(int i = 0; i < I; i++)
  for (int j = 0; j < J; j++)
    A( row(i,j), column(i,j)         


        

Answer 1

I'm not a fan of template meta-programming, so you may want to take this answer with a pinch of salt. But, before I invested any time on this problem, I'd ask myself the following:

1. Is my for loop a bottleneck?
2. Is unrolling it going to make any difference? Easily tested by hand-unrolling and measuring.

In many compilers/cpus, the "looped" version can give better performance due to cache effects.

Remember: Measure first, optimise later - if at all.