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Count grouped mantissas for each block all at once at the end of bit

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allocation for each block.
24% faster in function bit_alloc(). Approx. 10% faster overall encoding.

Originally committed as revision 26039 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2010-12-16 22:47:04 +00:00
parent e7536ac567
commit 126a29b871
1 changed files with 34 additions and 41 deletions
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75
libavcodec/ac3enc.c
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@ -915,56 +915,44 @@ static void count_frame_bits(AC3EncodeContext *s)
/**
* Calculate the number of bits needed to encode a set of mantissas.
*/
static int compute_mantissa_size(AC3EncodeContext *s, uint8_t *bap, int nb_coefs)
static int compute_mantissa_size(int mant_cnt[5], uint8_t *bap, int nb_coefs)
{
int bits, b, i;
bits = 0;
for (i = 0; i < nb_coefs; i++) {
b = bap[i];
switch (b) {
case 0:
/* bap=0 mantissas are not encoded */
break;
case 1:
/* 3 mantissas in 5 bits */
if (s->mant1_cnt == 0)
bits += 5;
if (++s->mant1_cnt == 3)
s->mant1_cnt = 0;
break;
case 2:
/* 3 mantissas in 7 bits */
if (s->mant2_cnt == 0)
bits += 7;
if (++s->mant2_cnt == 3)
s->mant2_cnt = 0;
break;
case 3:
bits += 3;
break;
case 4:
/* 2 mantissas in 7 bits */
if (s->mant4_cnt == 0)
bits += 7;
if (++s->mant4_cnt == 2)
s->mant4_cnt = 0;
break;
case 14:
bits += 14;
break;
case 15:
bits += 16;
break;
default:
if (b <= 4) {
// bap=1 to bap=4 will be counted in compute_mantissa_size_final
mant_cnt[b]++;
} else if (b <= 13) {
// bap=5 to bap=13 use (bap-1) bits
bits += b - 1;
break;
} else {
// bap=14 uses 14 bits and bap=15 uses 16 bits
bits += (b == 14) ? 14 : 16;
}
}
return bits;
}
/**
* Finalize the mantissa bit count by adding in the grouped mantissas.
*/
static int compute_mantissa_size_final(int mant_cnt[5])
{
// bap=1 : 3 mantissas in 5 bits
int bits = (mant_cnt[1] / 3) * 5;
// bap=2 : 3 mantissas in 7 bits
// bap=4 : 2 mantissas in 7 bits
bits += ((mant_cnt[2] / 3) + (mant_cnt[4] >> 1)) * 7;
// bap=3 : each mantissa is 3 bits
bits += mant_cnt[3] * 3;
return bits;
}
/**
* Calculate masking curve based on the final exponents.
* Also calculate the power spectral densities to use in future calculations.
@ -1025,6 +1013,7 @@ static int bit_alloc(AC3EncodeContext *s,
{
int blk, ch;
int mantissa_bits;
int mant_cnt[5];
snr_offset = (snr_offset - 240) << 2;
@ -1032,16 +1021,20 @@ static int bit_alloc(AC3EncodeContext *s,
mantissa_bits = 0;
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk];
s->mant1_cnt = 0;
s->mant2_cnt = 0;
s->mant4_cnt = 0;
// initialize grouped mantissa counts. these are set so that they are
// padded to the next whole group size when bits are counted in
// compute_mantissa_size_final
mant_cnt[0] = mant_cnt[3] = 0;
mant_cnt[1] = mant_cnt[2] = 2;
mant_cnt[4] = 1;
for (ch = 0; ch < s->channels; ch++) {
ff_ac3_bit_alloc_calc_bap(block->mask[ch], block->psd[ch], 0,
s->nb_coefs[ch], snr_offset,
s->bit_alloc.floor, ff_ac3_bap_tab,
block->bap[ch]);
mantissa_bits += compute_mantissa_size(s, block->bap[ch], s->nb_coefs[ch]);
mantissa_bits += compute_mantissa_size(mant_cnt, block->bap[ch], s->nb_coefs[ch]);
}
mantissa_bits += compute_mantissa_size_final(mant_cnt);
}
return mantissa_bits;
}