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avcodec/mpeg12dec: Revert Change to mpeg2_fast_decode_block_non_intra

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This fixes the speed regression from 20626f53e9
and still checks sufficiently to prevent out of allocated memory accesses
due to the index

Before:
1823 decicycles in mpeg2_fast_decode_block_non_intra, 8388493 runs, 115 skips
After:
1808 decicycles in mpeg2_fast_decode_block_non_intra, 8388494 runs, 114 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 6a92598e14
commit 7667afffb8
1 changed files with 1 additions and 3 deletions
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4
libavcodec/mpeg12dec.c
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@ -474,7 +474,6 @@ static inline int mpeg2_fast_decode_block_non_intra(MpegEncContext *s,
if (level != 0) {
i += run;
check_scantable_index(s, i);
j = scantable[i];
level = ((level * 2 + 1) * qscale) >> 1;
level = (level ^ SHOW_SBITS(re, &s->gb, 1)) - SHOW_SBITS(re, &s->gb, 1);
@ -486,7 +485,6 @@ static inline int mpeg2_fast_decode_block_non_intra(MpegEncContext *s,
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 * 2 + 1) * qscale) >> 1;
@ -497,7 +495,7 @@ static inline int mpeg2_fast_decode_block_non_intra(MpegEncContext *s,
}
block[j] = level;
if (((int32_t)GET_CACHE(re, &s->gb)) <= (int32_t)0xBFFFFFFF)
if (((int32_t)GET_CACHE(re, &s->gb)) <= (int32_t)0xBFFFFFFF || i > 63)
break;
UPDATE_CACHE(re, &s->gb);