Fusing a triangle loop for parallelization, calculating sub-indices

Question

A common technique in parallelization is to fuse nested for loops like this

for(int i=0; i

to

Answer 1

The most sane form is of course the first form.

That said, the fused form is better done with conditionals:

int i = 0; int j = 0;
for(int x=0; x<(n*(n+1)/2); x++) {
  // ...
  ++j;
  if (j>i)
  {
    j = 0;
    ++i;
  }
}