On Tue, Jan 5, 2016 at 7:44 AM, Daniel Serpell <dserp...@gmail.com> wrote: > Hi!, > > El Mon, Jan 04, 2016 at 06:33:59PM -0800, Ganesh Ajjanagadde escribio: >> This exploits an approach based on the sieve of Eratosthenes, a popular >> method for generating prime numbers. >> >> Tables are identical to previous ones. >> >> Tested with FATE with/without --enable-hardcoded-tables. >> >> Sample benchmark (Haswell, GNU/Linux+gcc): >> prev: >> 7860100 decicycles in cbrt_tableinit, 1 runs, 0 skips >> 7777490 decicycles in cbrt_tableinit, 2 runs, 0 skips >> [...] >> 7582339 decicycles in cbrt_tableinit, 256 runs, 0 skips >> 7563556 decicycles in cbrt_tableinit, 512 runs, 0 skips >> >> new: >> 2099480 decicycles in cbrt_tableinit, 1 runs, 0 skips >> 2044470 decicycles in cbrt_tableinit, 2 runs, 0 skips >> [...] >> 1796544 decicycles in cbrt_tableinit, 256 runs, 0 skips >> 1791631 decicycles in cbrt_tableinit, 512 runs, 0 skips >> > > See attached code, function "test1", based on an approximation of: > > (i+1)^(1/3) ~= i^(1/3) * ( 1 + 1/(3i) - 1/(9i) + 5/(81i) - .... )
I assume 1/(3i), 1/(9i^2), etc obtained via a Taylor series at x = 0. > > Generated values are the same as original floats (max error in double > is < 4*10^-10), it is faster (and I think, simpler) than your version. Had thought of these ideas, but did not examine as I was a little concerned about accuracy. Thanks, will give it a spin. Or alternatively, you can submit a patch since you put it into action. Alternatively, one could directly expand the series for (i+1)^(4/3). And it may be possible to tighten the number of terms needed by expanding not about x = 0, but x = i to get i+1. Or fancier polynomial approximations can be used. Have you tried these? > > Perhaps altering the constants it could be made faster still, but it is > currently dominated by de division in the main loop. Thanks for letting me know. > > Daniel. > > _______________________________________________ > 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
