[cfe-dev] Bug with vectorization of transcendental functions

Olaf Krzikalla olaf.krzikalla at tu-dresden.de
Thu Aug 21 06:42:29 PDT 2014

Am 19.08.2014 23:31, schrieb Ian Bell:
> The example shows
> what *not* to do, would be great if you could come up with an example of
> best practices.  If you could, I well might use your library.  What's
> the expected speedup for AVX for instance?
You just cannot give a general answer to that question. Not even an 
estimation. The only thing you can state for sure is that vectorization 
shifts the performance from being compute-bound toward being 
memory-bound. So if your algorithm is already memory-bound, you will not 
see any effect at all (in rare circumstances it might even decrease the 
performance). In other cases (e.g. reductions without any memory 
footprint) you might get practical speedups above the theoretical 
maximum (e.g. more than 8x for float on AVX).
It just depends on too many factors to state any expected speedups in a 
best practice guide of a general-purpose library.

Best Olaf

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