diff options
| author | foo86 <foobaz86@gmail.com> | 2017-07-10 17:11:39 +0300 |
|---|---|---|
| committer | James Almer <jamrial@gmail.com> | 2017-07-18 21:04:58 -0300 |
| commit | 902cd30e9b72d3ad5dfe01b27e3dd0928ad88562 (patch) | |
| tree | 09e7aa2db7abd730cebbf2115199267c95bd078f /libavcodec | |
| parent | 07a7f08b1e4b4679a3f9a60ecc45cae5078bc414 (diff) | |
| download | ffmpeg-902cd30e9b72d3ad5dfe01b27e3dd0928ad88562.tar.gz | |
avcodec/dca_core: probe extension headers directly
Avoid using bitstream reader in a non-standard way by directly accessing
index. Use bit shifting/masking operations instead.
Signed-off-by: James Almer <jamrial@gmail.com>
Diffstat (limited to 'libavcodec')
| -rw-r--r-- | libavcodec/dca_core.c | 31 |
1 files changed, 16 insertions, 15 deletions
diff --git a/libavcodec/dca_core.c b/libavcodec/dca_core.c index 090191dfa9..4a7ea4e3f3 100644 --- a/libavcodec/dca_core.c +++ b/libavcodec/dca_core.c @@ -1704,6 +1704,7 @@ static int parse_optional_info(DCACoreDecoder *s) int sync_pos = FFMIN(s->frame_size / 4, s->gb.size_in_bits / 32) - 1; int last_pos = get_bits_count(&s->gb) / 32; int size, dist; + uint32_t w1, w2 = 0; // Search for extension sync words aligned on 4-byte boundary. Search // must be done backwards from the end of core frame to work around @@ -1718,15 +1719,15 @@ static int parse_optional_info(DCACoreDecoder *s) // compatibility with legacy bitstreams. Minimum XCH frame size is // 96 bytes. AMODE and PCHS are further checked to reduce // probability of alias sync detection. - for (; sync_pos >= last_pos; sync_pos--) { - if (AV_RB32(s->gb.buffer + sync_pos * 4) == DCA_SYNCWORD_XCH) { - s->gb.index = (sync_pos + 1) * 32; - size = get_bits(&s->gb, 10) + 1; + for (; sync_pos >= last_pos; sync_pos--, w2 = w1) { + w1 = AV_RB32(s->gb.buffer + sync_pos * 4); + if (w1 == DCA_SYNCWORD_XCH) { + size = (w2 >> 22) + 1; dist = s->frame_size - sync_pos * 4; if (size >= 96 && (size == dist || size - 1 == dist) - && get_bits(&s->gb, 7) == 0x08) { - s->xch_pos = get_bits_count(&s->gb); + && (w2 >> 15 & 0x7f) == 0x08) { + s->xch_pos = sync_pos * 32 + 49; break; } } @@ -1743,13 +1744,13 @@ static int parse_optional_info(DCACoreDecoder *s) // The distance between X96 sync word and end of the core frame // must be equal to X96 frame size. Minimum X96 frame size is 96 // bytes. - for (; sync_pos >= last_pos; sync_pos--) { - if (AV_RB32(s->gb.buffer + sync_pos * 4) == DCA_SYNCWORD_X96) { - s->gb.index = (sync_pos + 1) * 32; - size = get_bits(&s->gb, 12) + 1; + for (; sync_pos >= last_pos; sync_pos--, w2 = w1) { + w1 = AV_RB32(s->gb.buffer + sync_pos * 4); + if (w1 == DCA_SYNCWORD_X96) { + size = (w2 >> 20) + 1; dist = s->frame_size - sync_pos * 4; if (size >= 96 && size == dist) { - s->x96_pos = get_bits_count(&s->gb); + s->x96_pos = sync_pos * 32 + 44; break; } } @@ -1768,10 +1769,10 @@ static int parse_optional_info(DCACoreDecoder *s) // XXCH frame header CRC must be valid. Minimum XXCH frame header // size is 11 bytes. - for (; sync_pos >= last_pos; sync_pos--) { - if (AV_RB32(s->gb.buffer + sync_pos * 4) == DCA_SYNCWORD_XXCH) { - s->gb.index = (sync_pos + 1) * 32; - size = get_bits(&s->gb, 6) + 1; + for (; sync_pos >= last_pos; sync_pos--, w2 = w1) { + w1 = AV_RB32(s->gb.buffer + sync_pos * 4); + if (w1 == DCA_SYNCWORD_XXCH) { + size = (w2 >> 26) + 1; dist = s->gb.size_in_bits / 8 - sync_pos * 4; if (size >= 11 && size <= dist && !av_crc(dca->crctab, 0xffff, s->gb.buffer + |