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281 lines
9.5 KiB
C
281 lines
9.5 KiB
C
/*
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* Common code between the AC-3 encoder and decoder
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* Copyright (c) 2000 Fabrice Bellard
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file libavcodec/ac3.c
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* Common code between the AC-3 encoder and decoder.
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*/
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#include "avcodec.h"
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#include "ac3.h"
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#include "get_bits.h"
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#if CONFIG_HARDCODED_TABLES
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/**
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* Starting frequency coefficient bin for each critical band.
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*/
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static const uint8_t band_start_tab[51] = {
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0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
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10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
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20, 21, 22, 23, 24, 25, 26, 27, 28, 31,
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34, 37, 40, 43, 46, 49, 55, 61, 67, 73,
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79, 85, 97, 109, 121, 133, 157, 181, 205, 229, 253
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};
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/**
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* Maps each frequency coefficient bin to the critical band that contains it.
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*/
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static const uint8_t bin_to_band_tab[253] = {
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0,
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1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
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13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
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25, 26, 27, 28, 28, 28, 29, 29, 29, 30, 30, 30,
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31, 31, 31, 32, 32, 32, 33, 33, 33, 34, 34, 34,
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35, 35, 35, 35, 35, 35, 36, 36, 36, 36, 36, 36,
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37, 37, 37, 37, 37, 37, 38, 38, 38, 38, 38, 38,
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39, 39, 39, 39, 39, 39, 40, 40, 40, 40, 40, 40,
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41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41,
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42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42,
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43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43, 43,
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44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44, 44,
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45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45,
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45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45,
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46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46,
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46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46,
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47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47,
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47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47,
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48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
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48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
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49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49,
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49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49, 49
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};
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#else /* CONFIG_HARDCODED_TABLES */
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static uint8_t band_start_tab[51];
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static uint8_t bin_to_band_tab[253];
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#endif
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static inline int calc_lowcomp1(int a, int b0, int b1, int c)
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{
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if ((b0 + 256) == b1) {
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a = c;
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} else if (b0 > b1) {
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a = FFMAX(a - 64, 0);
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}
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return a;
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}
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static inline int calc_lowcomp(int a, int b0, int b1, int bin)
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{
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if (bin < 7) {
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return calc_lowcomp1(a, b0, b1, 384);
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} else if (bin < 20) {
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return calc_lowcomp1(a, b0, b1, 320);
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} else {
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return FFMAX(a - 128, 0);
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}
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}
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void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
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int16_t *band_psd)
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{
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int bin, band;
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/* exponent mapping to PSD */
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for (bin = start; bin < end; bin++) {
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psd[bin]=(3072 - (exp[bin] << 7));
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}
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/* PSD integration */
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bin = start;
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band = bin_to_band_tab[start];
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do {
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int v = psd[bin++];
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int band_end = FFMIN(band_start_tab[band+1], end);
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for (; bin < band_end; bin++) {
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/* logadd */
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int adr = FFMIN(FFABS(v - psd[bin]) >> 1, 255);
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v = FFMAX(v, psd[bin]) + ff_ac3_log_add_tab[adr];
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}
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band_psd[band++] = v;
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} while (end > band_start_tab[band]);
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}
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int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,
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int start, int end, int fast_gain, int is_lfe,
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int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
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uint8_t *dba_lengths, uint8_t *dba_values,
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int16_t *mask)
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{
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int16_t excite[50]; /* excitation */
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int band;
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int band_start, band_end, begin, end1;
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int lowcomp, fastleak, slowleak;
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/* excitation function */
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band_start = bin_to_band_tab[start];
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band_end = bin_to_band_tab[end-1] + 1;
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if (band_start == 0) {
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lowcomp = 0;
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lowcomp = calc_lowcomp1(lowcomp, band_psd[0], band_psd[1], 384);
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excite[0] = band_psd[0] - fast_gain - lowcomp;
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lowcomp = calc_lowcomp1(lowcomp, band_psd[1], band_psd[2], 384);
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excite[1] = band_psd[1] - fast_gain - lowcomp;
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begin = 7;
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for (band = 2; band < 7; band++) {
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if (!(is_lfe && band == 6))
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lowcomp = calc_lowcomp1(lowcomp, band_psd[band], band_psd[band+1], 384);
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fastleak = band_psd[band] - fast_gain;
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slowleak = band_psd[band] - s->slow_gain;
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excite[band] = fastleak - lowcomp;
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if (!(is_lfe && band == 6)) {
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if (band_psd[band] <= band_psd[band+1]) {
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begin = band + 1;
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break;
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}
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}
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}
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end1 = FFMIN(band_end, 22);
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for (band = begin; band < end1; band++) {
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if (!(is_lfe && band == 6))
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lowcomp = calc_lowcomp(lowcomp, band_psd[band], band_psd[band+1], band);
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fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
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slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
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excite[band] = FFMAX(fastleak - lowcomp, slowleak);
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}
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begin = 22;
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} else {
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/* coupling channel */
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begin = band_start;
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fastleak = (s->cpl_fast_leak << 8) + 768;
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slowleak = (s->cpl_slow_leak << 8) + 768;
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}
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for (band = begin; band < band_end; band++) {
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fastleak = FFMAX(fastleak - s->fast_decay, band_psd[band] - fast_gain);
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slowleak = FFMAX(slowleak - s->slow_decay, band_psd[band] - s->slow_gain);
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excite[band] = FFMAX(fastleak, slowleak);
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}
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/* compute masking curve */
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for (band = band_start; band < band_end; band++) {
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int tmp = s->db_per_bit - band_psd[band];
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if (tmp > 0) {
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excite[band] += tmp >> 2;
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}
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mask[band] = FFMAX(ff_ac3_hearing_threshold_tab[band >> s->sr_shift][s->sr_code], excite[band]);
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}
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/* delta bit allocation */
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if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) {
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int i, seg, delta;
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if (dba_nsegs >= 8)
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return -1;
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band = 0;
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for (seg = 0; seg < dba_nsegs; seg++) {
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band += dba_offsets[seg];
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if (band >= 50 || dba_lengths[seg] > 50-band)
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return -1;
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if (dba_values[seg] >= 4) {
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delta = (dba_values[seg] - 3) << 7;
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} else {
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delta = (dba_values[seg] - 4) << 7;
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}
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for (i = 0; i < dba_lengths[seg]; i++) {
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mask[band++] += delta;
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}
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}
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}
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return 0;
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}
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void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
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int snr_offset, int floor,
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const uint8_t *bap_tab, uint8_t *bap)
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{
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int bin, band;
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/* special case, if snr offset is -960, set all bap's to zero */
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if (snr_offset == -960) {
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memset(bap, 0, 256);
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return;
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}
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bin = start;
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band = bin_to_band_tab[start];
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do {
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int m = (FFMAX(mask[band] - snr_offset - floor, 0) & 0x1FE0) + floor;
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int band_end = FFMIN(band_start_tab[band+1], end);
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for (; bin < band_end; bin++) {
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int address = av_clip((psd[bin] - m) >> 5, 0, 63);
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bap[bin] = bap_tab[address];
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}
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} while (end > band_start_tab[band++]);
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}
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/* AC-3 bit allocation. The algorithm is the one described in the AC-3
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spec. */
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void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
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int8_t *exp, int start, int end,
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int snr_offset, int fast_gain, int is_lfe,
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int dba_mode, int dba_nsegs,
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uint8_t *dba_offsets, uint8_t *dba_lengths,
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uint8_t *dba_values)
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{
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int16_t psd[256]; /* scaled exponents */
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int16_t band_psd[50]; /* interpolated exponents */
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int16_t mask[50]; /* masking value */
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ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, band_psd);
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ff_ac3_bit_alloc_calc_mask(s, band_psd, start, end, fast_gain, is_lfe,
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dba_mode, dba_nsegs, dba_offsets, dba_lengths,
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dba_values, mask);
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ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snr_offset, s->floor,
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ff_ac3_bap_tab, bap);
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}
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/**
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* Initializes some tables.
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* note: This function must remain thread safe because it is called by the
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* AVParser init code.
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*/
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av_cold void ac3_common_init(void)
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{
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#if !CONFIG_HARDCODED_TABLES
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/* compute bndtab and masktab from bandsz */
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int bin = 0, band;
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for (band = 0; band < 50; band++) {
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int band_end = bin + ff_ac3_critical_band_size_tab[band];
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band_start_tab[band] = bin;
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while (bin < band_end)
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bin_to_band_tab[bin++] = band;
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}
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band_start_tab[50] = bin;
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#endif /* !CONFIG_HARDCODED_TABLES */
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}
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