From e86ea34daddbc46ae06c1d4868eeb2750c0ad1b9 Mon Sep 17 00:00:00 2001 From: Justin Ruggles Date: Thu, 16 Dec 2010 21:09:22 +0000 Subject: [PATCH] Use a LUT for number of exponent groups. This avoids recalculating it for every block and channel for every frame. Originally committed as revision 26037 to svn://svn.ffmpeg.org/ffmpeg/trunk --- libavcodec/ac3enc.c | 48 ++++++++++++++++++++++++++++++++++-------------- 1 file changed, 34 insertions(+), 14 deletions(-) diff --git a/libavcodec/ac3enc.c b/libavcodec/ac3enc.c index 4a464a1c3..5d00dfdf6 100644 --- a/libavcodec/ac3enc.c +++ b/libavcodec/ac3enc.c @@ -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. @@ -484,6 +489,20 @@ 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 * by adjusting the exponents by the exponent shift values. @@ -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; -- 2.11.0