[FFmpeg-devel] [PATCH] avcodec/vp9: Fix undefined shifts in decode_frame_header()

[Ronald S. Bultje]

Hi,

On Thu, Mar 12, 2015 at 9:41 AM, Michael Niedermayer <michaelni at gmx.at>
wrote:

> On Thu, Mar 12, 2015 at 07:15:47AM -0400, Ronald S. Bultje wrote:
> > Hi,
> >
> > On Wed, Mar 11, 2015 at 9:11 PM, Michael Niedermayer <michaelni at gmx.at>
> > wrote:
> >
> > > Found-by: Clang -fsanitize=shift
> > > Reported-by: Thierry Foucu <tfoucu at google.com>
> > > Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> > > ---
> > >  libavcodec/vp9.c |    4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/libavcodec/vp9.c b/libavcodec/vp9.c
> > > index 265dc7e..0405c05 100644
> > > --- a/libavcodec/vp9.c
> > > +++ b/libavcodec/vp9.c
> > > @@ -689,10 +689,10 @@ static int decode_frame_header(AVCodecContext
> *ctx,
> > >          for (j = 1; j < 4; j++) {
> > >              s->segmentation.feat[i].lflvl[j][0] =
> > >                  av_clip_uintp2(lflvl + ((s->lf_delta.ref[j] +
> > > -                                         s->lf_delta.mode[0]) << sh),
> 6);
> > > +                                         s->lf_delta.mode[0]) * (1 <<
> > > sh)), 6);
> > >              s->segmentation.feat[i].lflvl[j][1] =
> > >                  av_clip_uintp2(lflvl + ((s->lf_delta.ref[j] +
> > > -                                         s->lf_delta.mode[1]) << sh),
> 6);
> > > +                                         s->lf_delta.mode[1]) * (1 <<
> > > sh)), 6);
> >
> >
> > Same question: why is this undefined?
>
> same awnser, left shifts of negative values are undefined in C
> if that was by someone forgetting to define it or intentional or they
> just didnt find a good definition in light of non twos-complement
> i do not know


But the values aren't negative?

Ronald