On Mon, Oct 12, 2015 at 7:46 AM, Carl Eugen Hoyos <ceho...@ag.or.at> wrote: > Ganesh Ajjanagadde <gajjanag <at> mit.edu> writes: > >> It is well known that fabs and fabsf are at least as fast and usually >> faster than the FFABS macro, at least on the gcc+glibc combination. > > I wasn't aware of this. > And I believe we support other compilers and other > libc implementations.
Indeed, which is why performance comparisons are welcome. I argue below why any sane configuration should not regress performance wise. This is also "relevant information" in my view. > >> For instance, see the reference: >> http://patchwork.sourceware.org/patch/6735/. >> This was a patch to glibc in order to remove their usages. Given their >> general performance obsession (more than FFmpeg in many cases), they >> have ensured that fabs and fabsf never peform worse than FFABS. > > Ok but is this really related? The reference is, the comment may not be, I was slightly annoyed at FFABS usage when libc provides them on all our platforms, and wanted a justification that would appeal to the FFmpeg crowd, namely peformance to move away from them. > >> I have tested on x86-64 Haswell with GCC 5.2 - even with no strict IEEE >> mode enabled, and just the standard -O3 optimizations, there is a >> performance benefit. > > This is the only relevant information imo. > Please provide (very, very short) information > on what you tested. Random integers, same style as before. I have not posted numbers, since my numbers are anyway meaningless: I lack non x86-64+(gcc/clang)+glibc configurations. As for that being the only relevant message, I do intend to shorten the message. The long stuff was simply my own personal motivation to make people understand why I did this stuff. Otherwise, I would have sent a separate message anyway in the patch thread, let me know what style you prefer. > > Since you mention libc so often: Does the patch > work on win*, aix and other strange platforms? Why not, any standard, conformant fabs/fabsf should. Again, I lack the configurations and am just a university student with a single laptop. fabs and fabsf are already being used elsewhere. Inf anything, they are far better specified on IEEE 754 than FFABS - behavior with NaN, Inf, etc. > > Carl Eugen > > _______________________________________________ > 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
