Traneptora/FFmpeg
1
Fork 0
forked from FFmpeg/FFmpeg
Code Pull requests Activity

Use a state machine to reduce branching logic in decode_cabac_residual.

Browse source 
Patch by Jason Garrett-Glaser (darkshikari gmail com)

Originally committed as revision 13060 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Jason Garrett-Glaser 2008-05-04 22:39:12 +00:00 • committed by Alexander Strange
parent e3e0d99332
commit 144783887c
1 changed files with 19 additions and 9 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

28
libavcodec/h264.c
View file

@ -5394,14 +5394,24 @@ static void decode_cabac_residual( H264Context *h, DCTELEM *block, int cat, int
9, 9,10,10, 8,11,12,11, 9, 9,10,10, 8,13,13, 9,
9,10,10, 8,13,13, 9, 9,10,10,14,14,14,14,14 }
};
/* node ctx: 0..3: abslevel1 (with abslevelgt1 == 0).
* 4..7: abslevelgt1 + 3 (and abslevel1 doesn't matter).
* map node ctx => cabac ctx for level=1 */
static const uint8_t coeff_abs_level1_ctx[8] = { 1, 2, 3, 4, 0, 0, 0, 0 };
/* map node ctx => cabac ctx for level>1 */
static const uint8_t coeff_abs_levelgt1_ctx[8] = { 5, 5, 5, 5, 6, 7, 8, 9 };
static const uint8_t coeff_abs_level_transition[2][8] = {
/* update node ctx after decoding a level=1 */
{ 1, 2, 3, 3, 4, 5, 6, 7 },
/* update node ctx after decoding a level>1 */
{ 4, 4, 4, 4, 5, 6, 7, 7 }
};
int index[64];
int av_unused last;
int coeff_count = 0;
int abslevel1 = 1;
int abslevelgt1 = 0;
int node_ctx = 0;
uint8_t *significant_coeff_ctx_base;
uint8_t *last_coeff_ctx_base;
@ -5495,20 +5505,22 @@ static void decode_cabac_residual( H264Context *h, DCTELEM *block, int cat, int
}
for( coeff_count--; coeff_count >= 0; coeff_count-- ) {
uint8_t *ctx = (abslevelgt1 != 0 ? 0 : FFMIN( 4, abslevel1 )) + abs_level_m1_ctx_base;
uint8_t *ctx = coeff_abs_level1_ctx[node_ctx] + abs_level_m1_ctx_base;
int j= scantable[index[coeff_count]];
if( get_cabac( CC, ctx ) == 0 ) {
node_ctx = coeff_abs_level_transition[0][node_ctx];
if( !qmul ) {
block[j] = get_cabac_bypass_sign( CC, -1);
}else{
block[j] = (get_cabac_bypass_sign( CC, -qmul[j]) + 32) >> 6;
}
abslevel1++;
} else {
int coeff_abs = 2;
ctx = 5 + FFMIN( 4, abslevelgt1 ) + abs_level_m1_ctx_base;
ctx = coeff_abs_levelgt1_ctx[node_ctx] + abs_level_m1_ctx_base;
node_ctx = coeff_abs_level_transition[1][node_ctx];
while( coeff_abs < 15 && get_cabac( CC, ctx ) ) {
coeff_abs++;
}
@ -5533,8 +5545,6 @@ static void decode_cabac_residual( H264Context *h, DCTELEM *block, int cat, int
if( get_cabac_bypass( CC ) ) block[j] = (-coeff_abs * qmul[j] + 32) >> 6;
else block[j] = ( coeff_abs * qmul[j] + 32) >> 6;
}
abslevelgt1++;
}
}
#ifdef CABAC_ON_STACK