how to pass/return Vc::Vector arguments to a function?

[Matthias Kretz]

On Mittwoch, 9. November 2016 13:06:30 CET you wrote:
> > BTW, is there significant data parallel work on the outer loop, too? In
> > this case you might consider vectorising the outer loop.
>
> there is, and in fact more than in the inner loop, thanks for pointing that
> out. the problem is that then i may be updating the same atom several
> times simultaneously, and i will need atomic operations…, i might give it a
> try though. 

Have you considered double-buffering. E.g.

state1 = initial_state();
while (...) {
  state2 = timestep(state1);
  state1 = timestep(state2);
}

That way you have one read-only and one write-only set of atoms. You'd get 
different results, but not necessarily less correct ones, no?

Alternatively, you can switch vectorization direction. I.e. vectorize the 
outer loop and keep the inner loop vectorization as is. When calling the inner 
loop, loop over the scalars in the Vc::Vectors of the outer loop. (Possibly, 
using a mask, like this:
for (int i : where(x > 0)) {
  // i will be all the indexes where x[i] > 0
  inner(x[i]);
}
)

Cheers,
  Matthias

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 Dr. Matthias Kretz                                https://kretzfamily.de
 GSI Helmholtzzentrum für Schwerionenforschung             https://gsi.de
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