• Ganesh Ajjanagadde's avatar
    lavc/aacenc_utils: replace powf(x,y) by expf(logf(x), y) · bccc81df
    Ganesh Ajjanagadde authored
    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. Made an inline function in lavu/internal.h for this
    purpose.
    
    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.
    Reviewed-by: 's avatarReimar Döffinger <Reimar.Doeffinger@gmx.de>
    Reviewed-by: 's avatarRonald S. Bultje <rsbultje@gmail.com>
    Signed-off-by: 's avatarGanesh Ajjanagadde <gajjanag@gmail.com>
    bccc81df
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