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| author | Ganesh Ajjanagadde <gajjanag@gmail.com> | 2016-02-29 22:16:16 -0500 |
|---|---|---|
| committer | Ganesh Ajjanagadde <gajjanag@gmail.com> | 2016-03-01 22:57:44 -0500 |
| commit | bd9c58756a50b52e495b748d6ea6b0aafe397c25 (patch) | |
| tree | 563c31812397bd1ebc8bd87caa62c032edf6c55d /libavcodec | |
| parent | 5324882529f322bc601a2d31a798489d160a01da (diff) | |
| download | ffmpeg-bd9c58756a50b52e495b748d6ea6b0aafe397c25.tar.gz | |
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>
Diffstat (limited to 'libavcodec')
| -rw-r--r-- | libavcodec/aacenc_utils.h | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/libavcodec/aacenc_utils.h b/libavcodec/aacenc_utils.h index cb5bc8da12..c2a2c2ec68 100644 --- a/libavcodec/aacenc_utils.h +++ b/libavcodec/aacenc_utils.h @@ -90,8 +90,7 @@ static inline float find_max_val(int group_len, int swb_size, const float *scale static inline int find_min_book(float maxval, int sf) { - float Q = ff_aac_pow2sf_tab[POW_SF2_ZERO - sf + SCALE_ONE_POS - SCALE_DIV_512]; - float Q34 = sqrtf(Q * sqrtf(Q)); + float Q34 = ff_aac_pow34sf_tab[POW_SF2_ZERO - sf + SCALE_ONE_POS - SCALE_DIV_512]; int qmaxval, cb; qmaxval = maxval * Q34 + C_QUANT; if (qmaxval >= (FF_ARRAY_ELEMS(aac_maxval_cb))) |