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branchless renormalization (1% faster get_cabac) old branchless renormalization wasnt faster because gcc was scared of the shift variable (missusing bit variable now) 

Originally committed as revision 6587 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2006-10-08 13:20:22 +00:00
parent 99ce10873d
commit 260ceb6322
2 changed files with 20 additions and 19 deletions
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18
libavcodec/cabac.c
View File

@ -73,22 +73,22 @@ const uint8_t ff_h264_lps_state[64]= {
}; };
const uint8_t ff_h264_norm_shift[256]= { const uint8_t ff_h264_norm_shift[256]= {
8,7,6,6,5,5,5,5,4,4,4,4,4,4,4,4, 9,8,7,7,6,6,6,6,5,5,5,5,5,5,5,5,
4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3, 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
}; };
/** /**

21
libavcodec/cabac.h
View File

@ -266,16 +266,16 @@ static void refill(CABACContext *c){
c->bytestream+= CABAC_BITS/8; c->bytestream+= CABAC_BITS/8;
} }
#if 0 /* all use commented */ #if 1 /* all use commented */
static void refill2(CABACContext *c){ static void refill2(CABACContext *c){
int i, x; int i, x;
x= c->low ^ (c->low-1); x= c->low ^ (c->low-1);
i= 8 - ff_h264_norm_shift[x>>(CABAC_BITS+1)]; i= 9 - ff_h264_norm_shift[x>>(CABAC_BITS+1)];
x= -CABAC_MASK; x= -CABAC_MASK;
if(c->bytestream < c->bytestream_end) if(c->bytestream <= c->bytestream_end)
#if CABAC_BITS == 16 #if CABAC_BITS == 16
x+= (c->bytestream[0]<<9) + (c->bytestream[1]<<1); x+= (c->bytestream[0]<<9) + (c->bytestream[1]<<1);
#else #else
@ -395,17 +395,18 @@ asm(
#endif #endif
renorm_cabac_decoder_once(c); renorm_cabac_decoder_once(c);
}else{ }else{
// int shift= ff_h264_norm_shift[RangeLPS>>17]; bit= ff_h264_norm_shift[RangeLPS>>17];
bit= (s&1)^1;
c->low -= c->range; c->low -= c->range;
*state= c->lps_state[s]; *state= c->lps_state[s];
c->range = RangeLPS; // c->range = RangeLPS;
renorm_cabac_decoder(c); // renorm_cabac_decoder(c);
/* c->range = RangeLPS<<shift; c->range = RangeLPS<<bit;
c->low <<= shift; c->low <<= bit;
bit= (s&1)^1;
if(!(c->low & 0xFFFF)){ if(!(c->low & 0xFFFF)){
refill2(c); refill2(c);
}*/ }
} }
#else #else
lps_mask= (c->range - c->low)>>31; lps_mask= (c->range - c->low)>>31;