[FFmpeg-devel] [PATCH] lavc/aacenc_utils: replace sqrtf(Q*sqrtf(Q)) by precomputed value

[Rostislav Pehlivanov]

On 1 March 2016 at 03:21, Ganesh Ajjanagadde <gajjanag at gmail.com> wrote:

> It makes no sense whatsoever to do this at each function call; we
> already have a table for this.
>
> Yields a 2x improvement in find_min_book (x86-64, Haswell+GCC):
> ffmpeg -i sin.flac -acodec aac -y sin.aac
> find_min_book
> old
>     605 decicycles in find_min_book, 8388453 runs,    155 skips.9x
>     606 decicycles in find_min_book,16776912 runs,    304 skips.9x
>     607 decicycles in find_min_book,33553819 runs,    613 skips.2x
>     607 decicycles in find_min_book,67107668 runs,   1196 skips.3x
>     607 decicycles in find_min_book,134215360 runs,   2368 skips3x
>
> new
>     359 decicycles in find_min_book, 8388552 runs,     56 skips.3x
>     360 decicycles in find_min_book,16777112 runs,    104 skips.1x
>     361 decicycles in find_min_book,33554218 runs,    214 skips.4x
>     361 decicycles in find_min_book,67108381 runs,    483 skips.5x
>     361 decicycles in find_min_book,134216725 runs,   1003 skips5x
>
> and more importantly a non-negligible speedup (~ 8%) to overall AAC
> encoding:
> old:
> ffmpeg -i sin.flac -acodec aac -strict -2 -y sin_new.aac  6.82s user 0.03s
> system 104% cpu 6.565 total
> new:
> ffmpeg -i sin.flac -acodec aac -strict -2 -y sin_old.aac  6.24s user 0.03s
> system 104% cpu 5.993 total
>
> Signed-off-by: Ganesh Ajjanagadde <gajjanag at gmail.com>
>

Nicely spotted, thanks.

LGTM, feel free to apply whenever you can.