On Fri, Dec 11, 2015 at 04:24:43PM -0500, Ganesh Ajjanagadde wrote: > On Fri, Dec 11, 2015 at 4:14 PM, Andreas Cadhalpun > <andreas.cadhal...@googlemail.com> wrote: > > On 07.12.2015 00:27, Ganesh Ajjanagadde wrote: > >> On Sun, Dec 6, 2015 at 6:12 PM, Andreas Cadhalpun > >> <andreas.cadhal...@googlemail.com> wrote: > >>> On 06.12.2015 22:48, Michael Niedermayer wrote: > >>>> my concern is more on h264 (CAVLC) and hevc speed > >>> > >>> I tested with 444_8bit_cavlc.h264 added 100 together with the concat > >>> demuxer, > >>> and couldn't see a measurable speed difference caused by this error check. > >> > >> Ok, so here is my understanding of the situation. > >> I think both of you are right, but have different perspectives on this. > >> So in practice a log < 7 may be usually predicted correctly, and the > >> compiler in all likelihood will continue to inline the function. Thus, > >> excepting the first run, there should not be an issue, and maybe the > >> compiler even feeds in the "likely" information for the first run > >> also. > >> > >> Nevertheless, I also understand Michael's perspective: h264 is > >> arguably one of the most important codecs as supplied by FFmpeg. Even > >> a 0.01% speedloss in some place should be done with extreme caution, > >> since over time these may accumulate to something more sizable, say > >> 0.5%. There should be a very good justification for it, and thus > >> Michael spends effort trying to ensure that the security issue is > >> fixed at identical asm. > > > > I wouldn't call this a security issue, it's just undefined behavior. > > Meant really from a theoretical perspective, since undefined means > anything can happen. Of course, in practice a distinction may be > drawn. But then again, I consider even these worthy of backport.
btw, if you feel something should be backported, dont hesitate to push cherry picked commits to the release branches (with cherry-pick -x) if you are unsure if somethig should be cherry picked, dont hesitate to ask [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Let us carefully observe those good qualities wherein our enemies excel us and endeavor to excel them, by avoiding what is faulty, and imitating what is excellent in them. -- Plutarch
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