On Thu, Nov 5, 2015 at 9:29 PM, Michael Niedermayer <mich...@niedermayer.cc> wrote: > On Wed, Nov 04, 2015 at 10:08:27PM -0500, Ganesh Ajjanagadde wrote: >> 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) >> 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. >> >> Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> >> --- >> libswresample/resample.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/libswresample/resample.c b/libswresample/resample.c >> index a2cbb48..5d32cc2 100644 >> --- a/libswresample/resample.c >> +++ b/libswresample/resample.c >> @@ -171,7 +171,7 @@ 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); >> + y *= 0.3635819 - 0.4891775 * cos(w) + 0.1365995 * >> (2*cos(w)*cos(w)-1) - 0.0106411 * (4*cos(w)*cos(w)*cos(w) - 3*cos(w)); > > i would use a temporary variable for cos(w) > either way LGTM > > thx
Ok, changed to temporary and pushed. Thanks for the review. > > [...] > -- > Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB > > Avoid a single point of failure, be that a person or equipment. > > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
