On Sat, Oct 10, 2015 at 5:32 PM, Henrik Gramner <hen...@gramner.com> wrote: > On Sat, Oct 10, 2015 at 11:06 PM, Ganesh Ajjanagadde > <gajjanaga...@gmail.com> wrote: >> This uses Stein's binary GCD algorithm: >> https://en.wikipedia.org/wiki/Binary_GCD_algorithm >> to get a reported 1.7-2.1x speedup over Euclidean GCD on standard >> architectures. >> Have not benchmarked, so I can't comment > > Before you submit a patch that's supposed to make something faster, > you should benchmark it to verify that it is in fact faster. Do this > with inputs of various sizes on both 32- and 64-bit architectures and > both with and without compilers that support __builtin_ctzll(v).
I did not do this because I don't know how to write a benchmark in C easily: for instance, printing out can lead to I/O time loss, and on O3, unless there is I/O, a function may not be evaluated at all due to the "as if" optimization rules. Another problem is that the function is small, so I can't just time a single call, there are cache issues with arrays, etc etc. Yes, I can do it - but it will take some effort. Also, the only compilers I have are clang and gcc, both of which have the builtin. I figured someone with a better array of tools and more knowledgable in writing benchmarks can trivially do this. Furthermore, at the moment, comparisons are incomplete: I don't care about Windows myself but one could trivially add the lines if one so desired (see my commit message). Lastly, I can't find any links on how to do benchmarks cleanly, efficiently, and accurately. I hoped that FFmpeg has some clean way of doing this, but all the methods I see are terribly ad-hoc. > _______________________________________________ > 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
