[FFmpeg-cvslog] r9749 - trunk/libavcodec/ac3dec.c
jbr
subversion
Thu Jul 19 04:04:05 CEST 2007
Author: jbr
Date: Thu Jul 19 04:04:05 2007
New Revision: 9749
Log:
new implementation of exponent decoding
Modified:
trunk/libavcodec/ac3dec.c
Modified: trunk/libavcodec/ac3dec.c
==============================================================================
--- trunk/libavcodec/ac3dec.c (original)
+++ trunk/libavcodec/ac3dec.c Thu Jul 19 04:04:05 2007
@@ -46,9 +46,8 @@ static const int nfchans_tbl[8] = { 2, 1
*/
static float scale_factors[25];
-static int8_t exp_1[128];
-static int8_t exp_2[128];
-static int8_t exp_3[128];
+/** table for grouping exponents */
+static uint8_t exp_ungroup_tbl[128][3];
static int16_t l3_quantizers_1[32];
static int16_t l3_quantizers_2[32];
@@ -267,30 +266,7 @@ static void generate_quantizers_table_3(
*/
static void ac3_tables_init(void)
{
- int i, j, v;
-
- /* Exponent Decoding Tables */
- for (i = 0; i < 5; i++) {
- v = i - 2;
- for (j = 0; j < 25; j++)
- exp_1[i * 25 + j] = v;
- }
-
- for (i = 0; i < 25; i++) {
- v = (i % 5) - 2;
- for (j = 0; j < 5; j++)
- exp_2[i * 5 + j] = v;
- }
-
- for (i = 0; i < 25; i++) {
- v = -2;
- for (j = 0; j < 5; j++)
- exp_3[i * 5 + j] = v++;
- }
-
- for (i = 125; i < 128; i++)
- exp_1[i] = exp_2[i] = exp_3[i] = 25;
- /* End Exponent Decoding Tables */
+ int i;
/* Quantizer ungrouping tables. */
// for level-3 quantizers
@@ -317,6 +293,14 @@ static void ac3_tables_init(void)
//generate scale factors
for (i = 0; i < 25; i++)
scale_factors[i] = pow(2.0, -(i + 15));
+
+ /* generate exponent tables
+ reference: Section 7.1.3 Exponent Decoding */
+ for(i=0; i<128; i++) {
+ exp_ungroup_tbl[i][0] = i / 25;
+ exp_ungroup_tbl[i][1] = (i % 25) / 5;
+ exp_ungroup_tbl[i][2] = (i % 25) % 5;
+ }
}
@@ -472,60 +456,30 @@ static void ac3_parse_bsi(AC3DecodeConte
* @param dexps Decoded exponents are stored in dexps
* @return Returns 0 if exponents are decoded successfully, -1 if error occurs
*/
-static int decode_exponents(GetBitContext *gb, int expstr, int ngrps, uint8_t absexp, uint8_t *dexps)
+static void decode_exponents(GetBitContext *gb, int expstr, int ngrps,
+ uint8_t absexp, uint8_t *dexps)
{
- int exps;
-
- while (ngrps--) {
- exps = get_bits(gb, 7);
-
- absexp += exp_1[exps];
- if (absexp > 24) {
- av_log(NULL, AV_LOG_ERROR, "Absolute Exponent > 24, ngrp = %d\n", ngrps);
- return -ngrps;
- }
- switch (expstr) {
- case EXP_D45:
- *(dexps++) = absexp;
- *(dexps++) = absexp;
- case EXP_D25:
- *(dexps++) = absexp;
- case EXP_D15:
- *(dexps++) = absexp;
- }
+ int i, j, grp, grpsize;
+ int dexp[256];
+ int expacc, prevexp;
- absexp += exp_2[exps];
- if (absexp > 24) {
- av_log(NULL, AV_LOG_ERROR, "Absolute Exponent > 24, ngrp = %d\n", ngrps);
- return -ngrps;
- }
- switch (expstr) {
- case EXP_D45:
- *(dexps++) = absexp;
- *(dexps++) = absexp;
- case EXP_D25:
- *(dexps++) = absexp;
- case EXP_D15:
- *(dexps++) = absexp;
- }
+ /* unpack groups */
+ grpsize = expstr + (expstr == EXP_D45);
+ for(grp=0,i=0; grp<ngrps; grp++) {
+ expacc = get_bits(gb, 7);
+ dexp[i++] = exp_ungroup_tbl[expacc][0];
+ dexp[i++] = exp_ungroup_tbl[expacc][1];
+ dexp[i++] = exp_ungroup_tbl[expacc][2];
+ }
- absexp += exp_3[exps];
- if (absexp > 24) {
- av_log(NULL, AV_LOG_ERROR, "Absolute Exponent > 24, ngrp = %d\n", ngrps);
- return -ngrps;
- }
- switch (expstr) {
- case EXP_D45:
- *(dexps++) = absexp;
- *(dexps++) = absexp;
- case EXP_D25:
- *(dexps++) = absexp;
- case EXP_D15:
- *(dexps++) = absexp;
+ /* convert to absolute exps and expand groups */
+ prevexp = absexp;
+ for(i=0; i<ngrps*3; i++) {
+ prevexp = av_clip(prevexp + dexp[i]-2, 0, 24);
+ for(j=0; j<grpsize; j++) {
+ dexps[(i*grpsize)+j] = prevexp;
}
}
-
- return 0;
}
/* Performs bit allocation.
@@ -1536,10 +1490,7 @@ static int ac3_parse_audio_block(AC3Deco
bit_alloc_flags = 64;
cplabsexp = get_bits(gb, 4) << 1;
ngrps = (ctx->cplendmant - ctx->cplstrtmant) / (3 << (ctx->cplexpstr - 1));
- if (decode_exponents(gb, ctx->cplexpstr, ngrps, cplabsexp, ctx->dcplexps + ctx->cplstrtmant)) {
- av_log(NULL, AV_LOG_ERROR, "error decoding coupling exponents\n");
- return -1;
- }
+ decode_exponents(gb, ctx->cplexpstr, ngrps, cplabsexp, ctx->dcplexps + ctx->cplstrtmant);
}
for (i = 0; i < nfchans; i++) /* fbw channel exponents */
@@ -1549,20 +1500,14 @@ static int ac3_parse_audio_block(AC3Deco
ngrps = (ctx->endmant[i] + grpsize - 4) / grpsize;
dexps = ctx->dexps[i];
dexps[0] = get_bits(gb, 4);
- if (decode_exponents(gb, ctx->chexpstr[i], ngrps, dexps[0], dexps + 1)) {
- av_log(NULL, AV_LOG_ERROR, "error decoding channel %d exponents\n", i);
- return -1;
- }
+ decode_exponents(gb, ctx->chexpstr[i], ngrps, dexps[0], dexps + 1);
skip_bits(gb, 2); /* skip gainrng */
}
if (ctx->lfeexpstr != EXP_REUSE) { /* lfe exponents */
bit_alloc_flags |= 32;
ctx->dlfeexps[0] = get_bits(gb, 4);
- if (decode_exponents(gb, ctx->lfeexpstr, 2, ctx->dlfeexps[0], ctx->dlfeexps + 1)) {
- av_log(NULL, AV_LOG_ERROR, "error decoding lfe exponents\n");
- return -1;
- }
+ decode_exponents(gb, ctx->lfeexpstr, 2, ctx->dlfeexps[0], ctx->dlfeexps + 1);
}
if (get_bits1(gb)) { /* bit allocation information */
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