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use the same table for ungrouping exponents and bap=2 mantissas

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Originally committed as revision 14525 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2008-08-03 19:24:04 +00:00
parent 2288834f87
commit 7417120b6f
1 changed files with 19 additions and 16 deletions
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35
libavcodec/ac3dec.c
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@ -44,8 +44,11 @@
/** Maximum possible frame size when the specification limit is ignored */ /** Maximum possible frame size when the specification limit is ignored */
#define AC3_MAX_FRAME_SIZE 21695 #define AC3_MAX_FRAME_SIZE 21695
/** table for grouping exponents */ /**
static uint8_t exp_ungroup_tab[128][3]; * table for ungrouping 3 values in 7 bits.
* used for exponents and bap=2 mantissas
*/
static uint8_t ungroup_3_in_7_bits_tab[128][3];
/** tables for ungrouping mantissas */ /** tables for ungrouping mantissas */
@ -135,6 +138,14 @@ static av_cold void ac3_tables_init(void)
{ {
int i; int i;
/* generate table for ungrouping 3 values in 7 bits
reference: Section 7.1.3 Exponent Decoding */
for(i=0; i<128; i++) {
ungroup_3_in_7_bits_tab[i][0] = i / 25;
ungroup_3_in_7_bits_tab[i][1] = (i % 25) / 5;
ungroup_3_in_7_bits_tab[i][2] = (i % 25) % 5;
}
/* generate grouped mantissa tables /* generate grouped mantissa tables
reference: Section 7.3.5 Ungrouping of Mantissas */ reference: Section 7.3.5 Ungrouping of Mantissas */
for(i=0; i<32; i++) { for(i=0; i<32; i++) {
@ -145,9 +156,9 @@ static av_cold void ac3_tables_init(void)
} }
for(i=0; i<128; i++) { for(i=0; i<128; i++) {
/* bap=2 mantissas */ /* bap=2 mantissas */
b2_mantissas[i][0] = symmetric_dequant( i / 25 , 5); b2_mantissas[i][0] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][0], 5);
b2_mantissas[i][1] = symmetric_dequant((i % 25) / 5, 5); b2_mantissas[i][1] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][1], 5);
b2_mantissas[i][2] = symmetric_dequant((i % 25) % 5, 5); b2_mantissas[i][2] = symmetric_dequant(ungroup_3_in_7_bits_tab[i][2], 5);
/* bap=4 mantissas */ /* bap=4 mantissas */
b4_mantissas[i][0] = symmetric_dequant(i / 11, 11); b4_mantissas[i][0] = symmetric_dequant(i / 11, 11);
@ -170,14 +181,6 @@ static av_cold void ac3_tables_init(void)
int v = (i >> 5) - ((i >> 7) << 3) - 5; int v = (i >> 5) - ((i >> 7) << 3) - 5;
dynamic_range_tab[i] = powf(2.0f, v) * ((i & 0x1F) | 0x20); dynamic_range_tab[i] = powf(2.0f, v) * ((i & 0x1F) | 0x20);
} }
/* generate exponent tables
reference: Section 7.1.3 Exponent Decoding */
for(i=0; i<128; i++) {
exp_ungroup_tab[i][0] = i / 25;
exp_ungroup_tab[i][1] = (i % 25) / 5;
exp_ungroup_tab[i][2] = (i % 25) % 5;
}
} }
@ -361,9 +364,9 @@ static void decode_exponents(GetBitContext *gbc, int exp_strategy, int ngrps,
group_size = exp_strategy + (exp_strategy == EXP_D45); group_size = exp_strategy + (exp_strategy == EXP_D45);
for(grp=0,i=0; grp<ngrps; grp++) { for(grp=0,i=0; grp<ngrps; grp++) {
expacc = get_bits(gbc, 7); expacc = get_bits(gbc, 7);
dexp[i++] = exp_ungroup_tab[expacc][0]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][0];
dexp[i++] = exp_ungroup_tab[expacc][1]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][1];
dexp[i++] = exp_ungroup_tab[expacc][2]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][2];
} }
/* convert to absolute exps and expand groups */ /* convert to absolute exps and expand groups */