On Thu, Dec 17, 2015 at 9:29 AM, Rostislav Pehlivanov <atomnu...@gmail.com> wrote: > This commit adds a raw integer log2 function (which directly maps to a > builtin). This was needed as the Daala entropy coding system requires a > raw log2 and the existing ff_log2 OR'd the argument with 1. > > The C implementation was taken from Daala's source code, which > got it from someplace else as a search reveals more similar > implementations. It was described as the fastest > implementation tested on a Pentium MMX, but considering its simplicity > this statement is still probably valid to this day.
Likely not the fastest, pretty confident a de-Bruijn based approach is faster on modern hardware: https://www.klittlepage.com/2013/12/21/twelve-days-2013-de-bruijn-sequences/, or just google for it. Nevertheless, I am willing to accept this for an initial patch: people who care about performance on non gcc/clang platforms can study this and do the needful. > > While the native Daala decoder is still in development, this required > piece might prove useful to other parts of the code, such as access to > the __builtin_clz. Don't want to duplicate work here, see https://ffmpeg.org/pipermail/ffmpeg-devel/2015-December/185350.html and discussion therein. I don't know if they should go into the same patch. Or put in other words, I will hold off on my end, go ahead with this stuff (with/without the stuff in the link). Once your patch is in, depending on whether/how you incorporate things, I will return to the patch. [...] _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
