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| author | Ganesh Ajjanagadde <gajjanagadde@gmail.com> | 2015-11-04 22:02:13 -0500 |
|---|---|---|
| committer | Ganesh Ajjanagadde <gajjanagadde@gmail.com> | 2015-11-05 21:52:40 -0500 |
| commit | c8780822bacc38a8d84c882d564b07dd152366ed (patch) | |
| tree | 594963f040c580cdd41a64fdfced3d555d039575 /libswresample | |
| parent | 7d6a4797f17f29ed6f48eecbf9c50ae99a8fb04d (diff) | |
| download | ffmpeg-c8780822bacc38a8d84c882d564b07dd152366ed.tar.gz | |
swresample/resample: speed up build_filter for Blackman-Nuttall filter
This uses the trigonometric double and triple angle formulae to avoid
repeated (expensive) evaluation of libc's cos().
Sample benchmark (x86-64, Haswell, GNU/Linux)
test: fate-swr-resample-dblp-44100-2626
old:
1104466600 decicycles in build_filter(loop 1000), 256 runs, 0 skips
1096765286 decicycles in build_filter(loop 1000), 512 runs, 0 skips
1070479590 decicycles in build_filter(loop 1000), 1024 runs, 0 skips
new:
588861423 decicycles in build_filter(loop 1000), 256 runs, 0 skips
591262754 decicycles in build_filter(loop 1000), 512 runs, 0 skips
577355145 decicycles in build_filter(loop 1000), 1024 runs, 0 skips
This results in small differences with the old expression:
difference (worst case on [0, 2*M_PI]), argmax 0.008:
max diff (relative): 0.000000000000157289807188
blackman_old(0.008): 0.000363951585488813192382
blackman_new(0.008): 0.000363951585488755946507
These are judged to be insignificant for the performance gain. PSNR to
reference file is unchanged up to second decimal point for instance.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Diffstat (limited to 'libswresample')
| -rw-r--r-- | libswresample/resample.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/libswresample/resample.c b/libswresample/resample.c index c881ed8f41..6f2ca982ea 100644 --- a/libswresample/resample.c +++ b/libswresample/resample.c @@ -73,7 +73,7 @@ static double bessel(double x){ static int build_filter(ResampleContext *c, void *filter, double factor, int tap_count, int alloc, int phase_count, int scale, int filter_type, int kaiser_beta){ int ph, i; - double x, y, w; + double x, y, w, t; double *tab = av_malloc_array(tap_count+1, sizeof(*tab)); const int center= (tap_count-1)/2; @@ -100,7 +100,8 @@ static int build_filter(ResampleContext *c, void *filter, double factor, int tap break;} case SWR_FILTER_TYPE_BLACKMAN_NUTTALL: w = 2.0*x / (factor*tap_count) + M_PI; - y *= 0.3635819 - 0.4891775 * cos(w) + 0.1365995 * cos(2*w) - 0.0106411 * cos(3*w); + t = cos(w); + y *= 0.3635819 - 0.4891775 * t + 0.1365995 * (2*t*t-1) - 0.0106411 * (4*t*t*t - 3*t); break; case SWR_FILTER_TYPE_KAISER: w = 2.0*x / (factor*tap_count*M_PI); |