avcodec/startcode: Avoid unaligned accesses

Up until now, ff_startcode_find_candidate_c() simply casts
an uint8_t* to uint64_t*/uint32_t* to read 64/32 bits at a time
in case HAVE_FAST_UNALIGNED is true. Yet this ignores the
alignment requirement of these types as well as effective type
rules of the C standard. This commit therefore replaces these
direct accesses with AV_RN64/32; this also improves
readability.

UBSan reported these unaligned accesses which happened in 233
FATE-tests involving H.264 and VC-1 (this has also been reported
in tickets #8138 and #8485); these tests are fixed by this commit.

The output of GCC with -O3 is unchanged for aarch64, loongarch,
ppc and x64 (as well as for arches like alpha for which
HAVE_FAST_UNALIGNED is never true in the first place).
There was only a slight difference for mips and arm.
I don't know about the speed impact of them.

Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

0 files changed, 0 insertions, 0 deletions