[FFmpeg-devel] [PATCH] swr/resample: use fma when it is faster

Ronald S. Bultje rsbultje at gmail.com
Mon Dec 14 04:25:29 CET 2015


On Sun, Dec 13, 2015 at 7:29 PM, Ganesh Ajjanagadde <gajjanag at mit.edu>

> The worst part is that it is a bad idea to do runtime dispatch on the
> fma() itself, as the function call overhead will be nonneglible, and
> so one can't create a helper API in avutil or elsewhere. Thus, it can
> only be used when a function is in a critical hotspot, where the
> duplication of code and maintainence burden can be justified for the
> performance benefits. I might be missing something here though.

You would DSP'ize the loop, not the single fma instruction, right?
Depending on the size of the array (i.e. the size variable), it may be ok.


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