lavc/aacenc_utils: replace sqrtf(Q*sqrtf(Q)) by precomputed value

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

This also improves accuracy of the expression by ~ 2 ulp in some cases.

Reviewed-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Reviewed-by: Rostislav Pehlivanov <atomnuker@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanag@gmail.com>

0 files changed, 0 insertions, 0 deletions