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eac3dec: use 16-bit pre-mantissas instead of 24-bit in AHT decoding. it is

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simpler and also fixes a bug in GAQ dequantization.

Originally committed as revision 18860 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles
2009-05-17 06:53:24 +00:00
parent db2f209352
commit 9a7a71ed4c
4 changed files with 32 additions and 31 deletions
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38
libavcodec/eac3dec.c
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@@ -66,18 +66,18 @@ typedef enum {
#define EAC3_SR_CODE_REDUCED 3
/** lrint(M_SQRT2*cos(2*M_PI/12)*(1<<23)) */
#define COEFF_0 10273905LL
/** lrint(M_SQRT2*cos(2*M_PI/12)*(1<<15)) */
#define COEFF_0 40132
/** lrint(M_SQRT2*cos(0*M_PI/12)*(1<<23)) = lrint(M_SQRT2*(1<<23)) */
#define COEFF_1 11863283LL
/** lrint(M_SQRT2*cos(0*M_PI/12)*(1<<15)) = lrint(M_SQRT2*(1<<15)) */
#define COEFF_1 46341
/** lrint(M_SQRT2*cos(5*M_PI/12)*(1<<23)) */
#define COEFF_2 3070444LL
/** lrint(M_SQRT2*cos(5*M_PI/12)*(1<<15)) */
#define COEFF_2 11994
/**
* Calculate 6-point IDCT of the pre-mantissas.
* All calculations are 24-bit fixed-point.
* All calculations are 16-bit fixed-point.
*/
static void idct6(int pre_mant[6])
{
@@ -86,9 +86,9 @@ static void idct6(int pre_mant[6])
odd1 = pre_mant[1] - pre_mant[3] - pre_mant[5];
even2 = ( pre_mant[2] * COEFF_0) >> 23;
tmp = ( pre_mant[4] * COEFF_1) >> 23;
odd0 = ((pre_mant[1] + pre_mant[5]) * COEFF_2) >> 23;
even2 = ( pre_mant[2] * COEFF_0) >> 15;
tmp = ( pre_mant[4] * COEFF_1) >> 15;
odd0 = ((pre_mant[1] + pre_mant[5]) * COEFF_2) >> 15;
even0 = pre_mant[0] + (tmp >> 1);
even1 = pre_mant[0] - tmp;
@@ -155,13 +155,13 @@ void ff_eac3_decode_transform_coeffs_aht_ch(AC3DecodeContext *s, int ch)
if (!hebap) {
/* zero-mantissa dithering */
for (blk = 0; blk < 6; blk++) {
s->pre_mantissa[ch][bin][blk] = (av_lfg_get(&s->dith_state) & 0x7FFFFF) - 0x400000;
s->pre_mantissa[ch][bin][blk] = (av_lfg_get(&s->dith_state) & 0x7FFF) - 0x4000;
}
} else if (hebap < 8) {
/* Vector Quantization */
int v = get_bits(gbc, bits);
for (blk = 0; blk < 6; blk++) {
s->pre_mantissa[ch][bin][blk] = ff_eac3_mantissa_vq[hebap][v][blk] << 8;
s->pre_mantissa[ch][bin][blk] = ff_eac3_mantissa_vq[hebap][v][blk];
}
} else {
/* Gain Adaptive Quantization */
@@ -175,22 +175,24 @@ void ff_eac3_decode_transform_coeffs_aht_ch(AC3DecodeContext *s, int ch)
for (blk = 0; blk < 6; blk++) {
int mant = get_sbits(gbc, gbits);
if (mant == -(1 << (gbits-1))) {
if (log_gain > 0 && mant == -(1 << (gbits-1))) {
/* large mantissa */
int b;
mant = get_sbits(gbc, bits-2+log_gain) << (26-log_gain-bits);
int mbits = bits - (2 - log_gain);
mant = get_sbits(gbc, mbits);
mant <<= (15 - (mbits - 1));
/* remap mantissa value to correct for asymmetric quantization */
if (mant >= 0)
b = 32768 >> (log_gain+8);
b = 32768 >> log_gain;
else
b = ff_eac3_gaq_remap_2_4_b[hebap-8][log_gain-1];
mant += (ff_eac3_gaq_remap_2_4_a[hebap-8][log_gain-1] * (mant>>8) + b) >> 7;
mant += ((ff_eac3_gaq_remap_2_4_a[hebap-8][log_gain-1] * mant) >> 15) + b;
} else {
/* small mantissa, no GAQ, or Gk=1 */
mant <<= 24 - bits;
mant <<= 15 - (bits-1);
if (!log_gain) {
/* remap mantissa value for no GAQ or Gk=1 */
mant += (ff_eac3_gaq_remap_1[hebap-8] * (mant>>8)) >> 7;
mant += (ff_eac3_gaq_remap_1[hebap-8] * mant) >> 15;
}
}
s->pre_mantissa[ch][bin][blk] = mant;