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I wonder why the cond version's time is not the same in both cases.

Doug Currie
– Doug Currie

2019-04-17 14:35:07 +00:00
Commented Apr 17, 2019 at 14:35
I think that, because res is not volatile, gcc can do many optimizations that are less effective as the size is increasing. When I add 'volatile' to res the times for the conditional are always around 2 sec. For modulo around 2 sec when power of 2 and not stable (above 4 sec, increasing with the size) otherwise.

J. Doe
– J. Doe

2019-04-17 15:05:31 +00:00
Commented Apr 17, 2019 at 15:05
I also noticed that in the case of non-volatile res, for 1024 size the conditional runs faster, in 1 sec, so I guess it's about 'good' and 'bad' sizes for the optimizations (or branch predictors?).

J. Doe
– J. Doe

2019-04-17 15:14:32 +00:00
Commented Apr 17, 2019 at 15:14

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