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Use a LUT for number of exponent groups. This avoids recalculating it for

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every block and channel for every frame.

Originally committed as revision 26037 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2010-12-16 21:09:22 +00:00
parent 834550ea0d
commit e86ea34dad
1 changed files with 34 additions and 14 deletions
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48
libavcodec/ac3enc.c
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@ -76,7 +76,6 @@ typedef struct AC3Block {
int16_t **band_psd; ///< psd per critical band
int16_t **mask; ///< masking curve
uint16_t **qmant; ///< quantized mantissas
uint8_t num_exp_groups[AC3_MAX_CHANNELS]; ///< number of exponent groups
uint8_t exp_strategy[AC3_MAX_CHANNELS]; ///< exponent strategies
int8_t exp_shift[AC3_MAX_CHANNELS]; ///< exponent shift values
} AC3Block;
@ -151,6 +150,12 @@ static int16_t sintab[64];
static int16_t xcos1[128];
static int16_t xsin1[128];
/**
* LUT for number of exponent groups.
* exponent_group_tab[exponent strategy-1][number of coefficients]
*/
uint8_t exponent_group_tab[3][256];
/**
* Adjust the frame size to make the average bit rate match the target bit rate.
@ -483,6 +488,20 @@ static void apply_mdct(AC3EncodeContext *s)
}
/**
* Initialize exponent tables.
*/
static av_cold void exponent_init(AC3EncodeContext *s)
{
int i;
for (i = 73; i < 256; i++) {
exponent_group_tab[0][i] = (i - 1) / 3;
exponent_group_tab[1][i] = (i + 2) / 6;
exponent_group_tab[2][i] = (i + 8) / 12;
}
}
/**
* Extract exponents from the MDCT coefficients.
* This takes into account the normalization that was done to the input samples
@ -607,14 +626,11 @@ static void exponent_min(uint8_t *exp, uint8_t *exp1, int n)
* Update the exponents so that they are the ones the decoder will decode.
*/
static void encode_exponents_blk_ch(uint8_t *exp,
int nb_exps, int exp_strategy,
uint8_t *num_exp_groups)
int nb_exps, int exp_strategy)
{
int group_size, nb_groups, i, k;
int nb_groups, i, k;
group_size = exp_strategy + (exp_strategy == EXP_D45);
*num_exp_groups = (nb_exps + (group_size * 3) - 4) / (3 * group_size);
nb_groups = *num_exp_groups * 3;
nb_groups = exponent_group_tab[exp_strategy-1][nb_exps] * 3;
/* for each group, compute the minimum exponent */
switch(exp_strategy) {
@ -697,8 +713,7 @@ static void encode_exponents(AC3EncodeContext *s)
block1++;
}
encode_exponents_blk_ch(block->exp[ch], s->nb_coefs[ch],
block->exp_strategy[ch],
&block->num_exp_groups[ch]);
block->exp_strategy[ch]);
/* copy encoded exponents for reuse case */
block2 = block + 1;
for (blk2 = blk+1; blk2 < blk1; blk2++, block2++) {
@ -720,7 +735,7 @@ static void encode_exponents(AC3EncodeContext *s)
static void group_exponents(AC3EncodeContext *s)
{
int blk, ch, i;
int group_size, bit_count;
int group_size, nb_groups, bit_count;
uint8_t *p;
int delta0, delta1, delta2;
int exp0, exp1;
@ -730,11 +745,11 @@ static void group_exponents(AC3EncodeContext *s)
AC3Block *block = &s->blocks[blk];
for (ch = 0; ch < s->channels; ch++) {
if (block->exp_strategy[ch] == EXP_REUSE) {
block->num_exp_groups[ch] = 0;
continue;
}
group_size = block->exp_strategy[ch] + (block->exp_strategy[ch] == EXP_D45);
bit_count += 4 + (block->num_exp_groups[ch] * 7);
nb_groups = exponent_group_tab[block->exp_strategy[ch]-1][s->nb_coefs[ch]];
bit_count += 4 + (nb_groups * 7);
p = block->exp[ch];
/* DC exponent */
@ -742,7 +757,7 @@ static void group_exponents(AC3EncodeContext *s)
block->grouped_exp[ch][0] = exp1;
/* remaining exponents are delta encoded */
for (i = 1; i <= block->num_exp_groups[ch]; i++) {
for (i = 1; i <= nb_groups; i++) {
/* merge three delta in one code */
exp0 = exp1;
exp1 = p[0];
@ -1317,6 +1332,8 @@ static void output_audio_block(AC3EncodeContext *s,
/* exponents */
for (ch = 0; ch < s->channels; ch++) {
int nb_groups;
if (block->exp_strategy[ch] == EXP_REUSE)
continue;
@ -1324,7 +1341,8 @@ static void output_audio_block(AC3EncodeContext *s,
put_bits(&s->pb, 4, block->grouped_exp[ch][0]);
/* exponent groups */
for (i = 1; i <= block->num_exp_groups[ch]; i++)
nb_groups = exponent_group_tab[block->exp_strategy[ch]-1][s->nb_coefs[ch]];
for (i = 1; i <= nb_groups; i++)
put_bits(&s->pb, 7, block->grouped_exp[ch][i]);
/* gain range info */
@ -1757,6 +1775,8 @@ static av_cold int ac3_encode_init(AVCodecContext *avctx)
set_bandwidth(s, avctx->cutoff);
exponent_init(s);
bit_alloc_init(s);
s->mdct.avctx = avctx;