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| author | Ganesh Ajjanagadde <gajjanag@gmail.com> | 2016-03-08 22:08:29 -0500 |
|---|---|---|
| committer | Ganesh Ajjanagadde <gajjanag@gmail.com> | 2016-03-10 21:29:56 -0500 |
| commit | 66edd8656b851a0c85ba25ec293cc66192c363ae (patch) | |
| tree | d7138925f9e98a269891dea1e6ede48372e86f6e | |
| parent | b2ab3398f59ed18a565063584f961ff84484d699 (diff) | |
| download | ffmpeg-66edd8656b851a0c85ba25ec293cc66192c363ae.tar.gz | |
lavc/lpc: exploit even symmetry of window function
Yields 2x improvement in function performance, and boosts aac encoding
speed by ~ 4% overall. Sample benchmark (Haswell+GCC under -march=native):
after:
ffmpeg -i sin.flac -acodec aac -y sin_new.aac 5.22s user 0.03s system 105% cpu 4.970 total
before:
ffmpeg -i sin.flac -acodec aac -y sin_new.aac 5.40s user 0.05s system 105% cpu 5.162 total
Reviewed-by: Rostislav Pehlivanov <atomnuker@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanag@gmail.com>
| -rw-r--r-- | libavcodec/lpc.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/libavcodec/lpc.c b/libavcodec/lpc.c index 3839119cc2..052aeaa191 100644 --- a/libavcodec/lpc.c +++ b/libavcodec/lpc.c @@ -176,9 +176,10 @@ double ff_lpc_calc_ref_coefs_f(LPCContext *s, const float *samples, int len, const double a = 0.5f, b = 1.0f - a; /* Apply windowing */ - for (i = 0; i < len; i++) { + for (i = 0; i <= len / 2; i++) { double weight = a - b*cos((2*M_PI*i)/(len - 1)); s->windowed_samples[i] = weight*samples[i]; + s->windowed_samples[len-1-i] = weight*samples[len-1-i]; } s->lpc_compute_autocorr(s->windowed_samples, len, order, autoc); |