Ronald, On Fri, Oct 14, 2016 at 10:01 AM, Ronald S. Bultje <rsbul...@gmail.com> wrote: > This is intended to workaround bug "665 Integer Divide Instruction May > Cause Unpredictable Behavior" on some early AMD CPUs, which causes a > div-by-zero in this codepath, such as reported in Mozilla bug #1293996. > > Note that this isn't guaranteed to fix the bug, since a compiler is free > to reorder instructions that don't depend on each other. However, it > appears to fix the bug in Firefox, and a similar patch was applied to > libvpx also (see Chrome bug #599899). >
I recently made a few additional changes as this regressed in chrome [1][2], but just like this change there's no guarantee it won't occur again. [1] https://chromium.googlesource.com/webm/libvpx/+/8b4210940ce4183d4cfded42c323612c0c6d1688 [2] https://chromium.googlesource.com/webm/libvpx/+/82ea74223771793628dbd812c2fd50afcfb8183a > --- > libavcodec/vp9.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > lgtm > diff --git a/libavcodec/vp9.c b/libavcodec/vp9.c > index cb2a4a2..3b72149 100644 > --- a/libavcodec/vp9.c > +++ b/libavcodec/vp9.c > @@ -3705,11 +3705,10 @@ static av_always_inline void adapt_prob(uint8_t *p, > unsigned ct0, unsigned ct1, > if (!ct) > return; > > + update_factor = FASTDIV(update_factor * FFMIN(ct, max_count), max_count); > p1 = *p; > - p2 = ((ct0 << 8) + (ct >> 1)) / ct; > + p2 = ((((int64_t) ct0) << 8) + (ct >> 1)) / ct; > p2 = av_clip(p2, 1, 255); > - ct = FFMIN(ct, max_count); > - update_factor = FASTDIV(update_factor * ct, max_count); > > // (p1 * (256 - update_factor) + p2 * update_factor + 128) >> 8 > *p = p1 + (((p2 - p1) * update_factor + 128) >> 8); > -- > 2.8.1 > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
