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2x faster ff_h264_init_cabac_states(), 4k cpu cycles less.

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Sadly this is just per slice so the speedup with normal files should be negligible.

Originally committed as revision 21859 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2010-02-16 23:43:08 +00:00
parent fc78b0cb7e
commit 59f733d1b1
1 changed files with 10 additions and 9 deletions
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19
libavcodec/h264_cabac.c
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@ -688,19 +688,20 @@ static const int8_t cabac_context_init_PB[3][460][2] =
void ff_h264_init_cabac_states(H264Context *h) {
MpegEncContext * const s = &h->s;
int i;
const int8_t (*tab)[2];
if( h->slice_type_nos == FF_I_TYPE ) tab = cabac_context_init_I;
else tab = cabac_context_init_PB[h->cabac_init_idc];
/* calculate pre-state */
for( i= 0; i < 460; i++ ) {
int pre;
if( h->slice_type_nos == FF_I_TYPE )
pre = av_clip( ((cabac_context_init_I[i][0] * s->qscale) >>4 ) + cabac_context_init_I[i][1], 1, 126 );
else
pre = av_clip( ((cabac_context_init_PB[h->cabac_init_idc][i][0] * s->qscale) >>4 ) + cabac_context_init_PB[h->cabac_init_idc][i][1], 1, 126 );
int pre = 2*(((tab[i][0] * s->qscale) >>4 ) + tab[i][1]) - 127;
if( pre <= 63 )
h->cabac_state[i] = 2 * ( 63 - pre ) + 0;
else
h->cabac_state[i] = 2 * ( pre - 64 ) + 1;
pre^= pre>>31;
if(pre > 124)
pre= 124 + (pre&1);
h->cabac_state[i] = pre;
}
}