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bitstream: Avoid undefined behavior in bitstream_skip()

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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-stable@libav.org
This commit is contained in:
Luca Barbato 2017-07-08 21:04:44 +02:00
parent fd92dafaff
commit 79f64f7ebc
1 changed files with 4 additions and 2 deletions
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6
libavcodec/bitstream.h
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@ -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;