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avcodec/mpeg12dec: Redesign index checks for mpeg2_fast_decode_block_intra

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This fixes the speed regression from 20626f53e9f41cb3db82329ed3db7d773cfa3a8f
and still checks sufficiently to prevent out of allocated memory accesses
due to the index

Before:
1681 decicycles in mpeg2_fast_decode_block_intra, 4194238 runs, 66 skips
After:
1658 decicycles in mpeg2_fast_decode_block_intra, 4194248 runs, 56 skips

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Michael Niedermayer 2014-01-26 02:53:17 +01:00
parent 20626f53e9
commit 6a92598e14
1 changed files with 1 additions and 3 deletions
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4
libavcodec/mpeg12dec.c
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@ -628,11 +628,10 @@ static inline int mpeg2_fast_decode_block_intra(MpegEncContext *s, int16_t *bloc
UPDATE_CACHE(re, &s->gb);
GET_RL_VLC(level, run, re, &s->gb, rl->rl_vlc[0], TEX_VLC_BITS, 2, 0);
if (level >= 64) {
if (level >= 64 || i > 63) {
break;
} else if (level != 0) {
i += run;
check_scantable_index(s, i);
j = scantable[i];
level = (level * qscale * quant_matrix[j]) >> 4;
level = (level ^ SHOW_SBITS(re, &s->gb, 1)) - SHOW_SBITS(re, &s->gb, 1);
@ -643,7 +642,6 @@ static inline int mpeg2_fast_decode_block_intra(MpegEncContext *s, int16_t *bloc
UPDATE_CACHE(re, &s->gb);
level = SHOW_SBITS(re, &s->gb, 12); SKIP_BITS(re, &s->gb, 12);
i += run;
check_scantable_index(s, i);
j = scantable[i];
if (level < 0) {
level = (-level * qscale * quant_matrix[j]) >> 4;