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optimize branchless C CABAC decoder

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Originally committed as revision 6607 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2006-10-09 20:44:11 +00:00
parent b420448e38
commit 2e1aee80f4
2 changed files with 12 additions and 3 deletions
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8
libavcodec/cabac.c
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@ -133,11 +133,19 @@ void ff_init_cabac_states(CABACContext *c, uint8_t const (*lps_range)[4],
c->mps_state[2*i+3]= 2*mps_state[i]+3;
if( i ){
#ifdef BRANCHLESS_CABAD
c->mps_state[-2*i-3]= 2*lps_state[i]+2; //FIXME yes this is not valid C but iam lazy, cleanup welcome
c->mps_state[-2*i-4]= 2*lps_state[i]+3;
}else{
c->mps_state[-2*i-3]= 3;
c->mps_state[-2*i-4]= 2;
#else
c->lps_state[2*i+2]= 2*lps_state[i]+2;
c->lps_state[2*i+3]= 2*lps_state[i]+3;
}else{
c->lps_state[2*i+2]= 3;
c->lps_state[2*i+3]= 2;
#endif
}
}
}

7
libavcodec/cabac.h
View File

@ -452,7 +452,7 @@ static int get_cabac(CABACContext *c, uint8_t * const state){
int bit, lps_mask attribute_unused;
c->range -= RangeLPS;
#if 1
#ifndef BRANCHLESS_CABAD
if(c->low < c->range){
bit= s&1;
*state= c->mps_state[s];
@ -475,8 +475,9 @@ static int get_cabac(CABACContext *c, uint8_t * const state){
c->low -= c->range & lps_mask;
c->range += (RangeLPS - c->range) & lps_mask;
bit= (s^lps_mask)&1;
*state= c->mps_state[s - (130&lps_mask)];
s^=lps_mask;
*state= c->mps_state[s];
bit= s&1;
lps_mask= ff_h264_norm_shift[c->range>>(CABAC_BITS+3)];
c->range<<= lps_mask;