On Wed, Mar 9, 2016 at 2:16 AM, Reimar Döffinger <reimar.doeffin...@gmx.de> wrote: > On 08.03.2016, at 04:48, Ganesh Ajjanagadde <gajja...@gmail.com> wrote: > >> + nzl += expf(logf(s / ethresh) * nzslope); > > Shouldn't log2f/exp2f be faster? > log2f at least has CPU support on x86 AFAICT.
I had tested this, and no, though it is still faster than powf. It still seems to rely on libm, note that we don't use -ffast-math and a look at https://github.com/lattera/glibc/tree/master/sysdeps/x86_64/fpu as well seems to say no. Problem is, GNU people like to prioritize "correctly rounded" behavior over fast, reasonably accurate code, sometimes to ludicruous degrees. Personally, I don't know why we don't use -ffast-math, not many seem to care that heavily on strict IEEE semantics. Maybe it leads to too much variation across platforms? > _______________________________________________ > 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
