[FFmpeg-devel] [PATCH] lavc/aacenc_utils: replace powf(x, y) by expf(logf(x), y)

[Rostislav Pehlivanov]

On 8 March 2016 at 03:48, Ganesh Ajjanagadde <gajjanag at gmail.com> wrote:

> This is ~2x faster for y not an integer on Haswell+GCC, and should
> generally be faster due to the fact that anyway powf essentially does
> this under the hood.
>
> Note that there are some accuracy differences, that should generally be
> negligible. In particular, FATE still passes on this platform.
>
> Results in ~ 7% speedup in aac encoding with -march=native, Haswell+GCC.
> before:
> ffmpeg -i sin.flac -acodec aac -y sin_new.aac  6.05s user 0.06s system
> 104% cpu 5.821 total
>
> after:
> ffmpeg -i sin.flac -acodec aac -y sin_new.aac  5.67s user 0.03s system
> 105% cpu 5.416 total
>
> This is also faster than an alternative approach that pulls in powf, gets
> rid of
> the crufty NaN checks and other special cases, exploits knowledge about
> the intervals, etc.
> This of course does not exclude smarter approaches; just suggests that
> there would need to be significant work on this front of lower utility than
> searches for hotspots elsewhere.


LGTM, thanks