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use table for converting dynamic range codes to scale factors

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Originally committed as revision 9889 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2007-08-04 03:27:05 +00:00
parent 5aefe3ebef
commit 3357ff338b
1 changed files with 13 additions and 5 deletions
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18
libavcodec/ac3dec.c
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@ -69,6 +69,9 @@ static const uint8_t qntztab[16] = {
5, 6, 7, 8, 9, 10, 11, 12, 14, 16 5, 6, 7, 8, 9, 10, 11, 12, 14, 16
}; };
/** dynamic range table. converts codes to scale factors. */
static float dynrng_tbl[256];
/* Adjustmens in dB gain */ /* Adjustmens in dB gain */
#define LEVEL_MINUS_3DB 0.7071067811865476 #define LEVEL_MINUS_3DB 0.7071067811865476
#define LEVEL_MINUS_4POINT5DB 0.5946035575013605 #define LEVEL_MINUS_4POINT5DB 0.5946035575013605
@ -235,6 +238,13 @@ static void ac3_tables_init(void)
b5_mantissas[i] = symmetric_dequant(i, 15); b5_mantissas[i] = symmetric_dequant(i, 15);
} }
/* generate dynamic range table
reference: Section 7.7.1 Dynamic Range Control */
for(i=0; i<256; i++) {
int v = (i >> 5) - ((i >> 7) << 3) - 5;
dynrng_tbl[i] = powf(2.0f, v) * ((i & 0x1F) | 0x20);
}
//generate scale factors //generate scale factors
for (i = 0; i < 25; i++) for (i = 0; i < 25; i++)
scale_factors[i] = pow(2.0, -i); scale_factors[i] = pow(2.0, -i);
@ -692,7 +702,7 @@ static int ac3_parse_audio_block(AC3DecodeContext *ctx, int blk)
int bit_alloc_flags = 0; int bit_alloc_flags = 0;
int8_t *dexps; int8_t *dexps;
int mstrcplco, cplcoexp, cplcomant; int mstrcplco, cplcoexp, cplcomant;
int dynrng, chbwcod, ngrps, cplabsexp, skipl; int chbwcod, ngrps, cplabsexp, skipl;
for (i = 0; i < nfchans; i++) /*block switch flag */ for (i = 0; i < nfchans; i++) /*block switch flag */
ctx->blksw[i] = get_bits1(gb); ctx->blksw[i] = get_bits1(gb);
@ -705,16 +715,14 @@ static int ac3_parse_audio_block(AC3DecodeContext *ctx, int blk)
} }
if (get_bits1(gb)) { /* dynamic range */ if (get_bits1(gb)) { /* dynamic range */
dynrng = get_sbits(gb, 8); ctx->dynrng = dynrng_tbl[get_bits(gb, 8)];
ctx->dynrng = (((dynrng & 0x1f) | 0x20) << 13) * pow(2.0, -(18 - (dynrng >> 5)));
} else if(blk == 0) { } else if(blk == 0) {
ctx->dynrng = 1.0; ctx->dynrng = 1.0;
} }
if(acmod == AC3_ACMOD_DUALMONO) { /* dynamic range 1+1 mode */ if(acmod == AC3_ACMOD_DUALMONO) { /* dynamic range 1+1 mode */
if(get_bits1(gb)) { if(get_bits1(gb)) {
dynrng = get_sbits(gb, 8); ctx->dynrng2 = dynrng_tbl[get_bits(gb, 8)];
ctx->dynrng2 = (((dynrng & 0x1f) | 0x20) << 13) * pow(2.0, -(18 - (dynrng >> 5)));
} else if(blk == 0) { } else if(blk == 0) {
ctx->dynrng2 = 1.0; ctx->dynrng2 = 1.0;
} }