Module: libav
Branch: master
Commit: 79f64f7ebc2b2b7030c6219914bc141cc03fd377
Author: Luca Barbato <lu_z...@gentoo.org>
Committer: Luca Barbato <lu_z...@gentoo.org>
Date: Sat Jul 8 21:04:44 2017 +0200
bitstream: Avoid undefined behavior in bitstream_skip()
Do not use skip_remaining() to fully wipe the cache, as this could do
a 64-bit shift of a 64-bit variable which is undefined behavior in C.
Instead set the related variables to zero directly.
Thanks to Uoti for pointing out the problem.
CC: libav-sta...@libav.org
---
libavcodec/bitstream.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/libavcodec/bitstream.h b/libavcodec/bitstream.h
index d6dd2b9..1b23cb2 100644
--- a/libavcodec/bitstream.h
+++ b/libavcodec/bitstream.h
@@ -239,11 +239,13 @@ static inline void skip_remaining(BitstreamContext *bc,
unsigned n)
/* Skip n bits in the buffer. */
static inline void bitstream_skip(BitstreamContext *bc, unsigned n)
{
- if (n <= bc->bits_left)
+ if (n < bc->bits_left)
skip_remaining(bc, n);
else {
n -= bc->bits_left;
- skip_remaining(bc, bc->bits_left);
+ bc->bits = 0;
+ bc->bits_left = 0;
+
if (n >= 64) {
unsigned skip = n / 8;
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