[FFmpeg-cvslog] avcodec/vc1_pred: Fix invalid shift in scaleforsame()

[Michael Niedermayer]

ffmpeg | branch: release/4.2 | Michael Niedermayer <michael at niedermayer.cc> | Wed Jul 10 23:27:19 2019 +0200| [7f71ebded4be2d290b5d606de6256ceac0c18b8e] | committer: Michael Niedermayer

avcodec/vc1_pred: Fix invalid shift in scaleforsame()

Fixes: left shift of negative value -1
Fixes: 15531/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VC1IMAGE_fuzzer-5759556258365440

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 6dfda35dd29d2e2a86554d2c05d957a09ab79b0c)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=7f71ebded4be2d290b5d606de6256ceac0c18b8e
---

 libavcodec/vc1_pred.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/vc1_pred.c b/libavcodec/vc1_pred.c
index 9e29b44a1f..16565063ea 100644
--- a/libavcodec/vc1_pred.c
+++ b/libavcodec/vc1_pred.c
@@ -178,7 +178,7 @@ static av_always_inline int scaleforsame(VC1Context *v, int i, int n /* MV */,
     brfd      = FFMIN(v->brfd, 3);
     scalesame = ff_vc1_b_field_mvpred_scales[0][brfd];
 
-    n = (n * scalesame >> 8) << hpel;
+    n = (n * scalesame >> 8) * (1 << hpel);
     return n;
 }