On Thu, Oct 29, 2015 at 4:46 PM, Michael Niedermayer <mich...@niedermayer.cc> wrote: > On Wed, Oct 28, 2015 at 10:48:14PM -0400, Ganesh Ajjanagadde wrote: >> This ensures that no undefined behavior is invoked, while retaining >> identical return values in all cases and at no loss of performance >> (identical asm on clang and gcc). >> Essentially, this patch exchanges undefined behavior with implementation >> defined behavior, a strict improvement. >> >> Rationale: >> 1. The ideal solution is to have the return type a uint64_t. This >> unfortunately requires an API change. >> 2. The only pathological behavior happens if both arguments are >> INT64_MIN, to the best of my knowledge. In such a case, the >> implementation defined behavior is invoked in the sense that UINT64_MAX >> is interpreted as INT64_MIN, which any reasonable implementation will >> do. In any case, any usage where both arguments are INT64_MIN is a >> fuzzer anyway. >> 3. Alternatives of checking, etc require branching and lose performance >> for no concrete gain - no client cares about av_gcd's actual value when >> both args are INT64_MIN. Even if it did, on sane platforms (e.g all the >> ones FFmpeg cares about), it produces a correct gcd, namely INT64_MIN. >> >> Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> >> --- >> libavutil/mathematics.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) > > LGTM
pushed, thanks. > > [...] > -- > 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 > > _______________________________________________ > 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
