On Thu, Nov 5, 2015 at 6:05 AM, Moritz Barsnick <barsn...@gmx.net> wrote: > On Wed, Nov 04, 2015 at 22:08:27 -0500, Ganesh Ajjanagadde wrote: >> This uses the trigonometric double and triple angle formulae to avoid >> repeated (expensive) evaluation of libc's cos(). > [...] >> - 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)); > > Q: Does the compilers' optimization ensure that cos(w) is evaluated > only once?
Why not? Any decent compiler should - cos is a function with no side effects, lending itself to "common subexpression elimination" or whatever they call it. > > Thanks, > Moritz > _______________________________________________ > 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
