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

[Michael Niedermayer]

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

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Those who are best at talking, realize last or never when they are wrong.
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