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https://github.com/FFmpeg/FFmpeg.git
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240 lines
7.5 KiB
C
240 lines
7.5 KiB
C
/*
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* Common code between AC3 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 ac3.c
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* Common code between AC3 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 "bitstream.h"
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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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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, i, j, k, end1, v;
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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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j=start;
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k=bin_to_band_tab[start];
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do {
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v=psd[j];
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j++;
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end1 = FFMIN(band_start_tab[k+1], end);
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for(i=j;i<end1;i++) {
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/* logadd */
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int adr = FFMIN(FFABS(v - psd[j]) >> 1, 255);
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v = FFMAX(v, psd[j]) + ff_ac3_log_add_tab[adr];
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j++;
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}
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band_psd[k]=v;
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k++;
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} while (end > band_start_tab[k]);
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}
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void 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 bin, k;
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int bndstrt, bndend, begin, end1, tmp;
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int lowcomp, fastleak, slowleak;
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/* excitation function */
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bndstrt = bin_to_band_tab[start];
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bndend = bin_to_band_tab[end-1] + 1;
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if (bndstrt == 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 (bin = 2; bin < 7; bin++) {
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if (!(is_lfe && bin == 6))
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lowcomp = calc_lowcomp1(lowcomp, band_psd[bin], band_psd[bin+1], 384);
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fastleak = band_psd[bin] - fast_gain;
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slowleak = band_psd[bin] - s->slow_gain;
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excite[bin] = fastleak - lowcomp;
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if (!(is_lfe && bin == 6)) {
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if (band_psd[bin] <= band_psd[bin+1]) {
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begin = bin + 1;
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break;
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}
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}
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}
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end1=bndend;
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if (end1 > 22) end1=22;
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for (bin = begin; bin < end1; bin++) {
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if (!(is_lfe && bin == 6))
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lowcomp = calc_lowcomp(lowcomp, band_psd[bin], band_psd[bin+1], bin);
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fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain);
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slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain);
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excite[bin] = 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 = bndstrt;
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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 (bin = begin; bin < bndend; bin++) {
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fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain);
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slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain);
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excite[bin] = FFMAX(fastleak, slowleak);
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}
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/* compute masking curve */
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for (bin = bndstrt; bin < bndend; bin++) {
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tmp = s->db_per_bit - band_psd[bin];
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if (tmp > 0) {
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excite[bin] += tmp >> 2;
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}
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mask[bin] = FFMAX(ff_ac3_hearing_threshold_tab[bin >> s->sr_shift][s->sr_code], excite[bin]);
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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 band, seg, delta;
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band = 0;
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for (seg = 0; seg < FFMIN(8, dba_nsegs); seg++) {
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band = FFMIN(49, band + dba_offsets[seg]);
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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 (k = 0; k < dba_lengths[seg]; k++) {
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mask[band] += delta;
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band++;
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}
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}
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}
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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, uint8_t *bap)
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{
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int i, j, k, end1, v, address;
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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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i = start;
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j = bin_to_band_tab[start];
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do {
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v = (FFMAX(mask[j] - snr_offset - floor, 0) & 0x1FE0) + floor;
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end1 = FFMIN(band_start_tab[j] + ff_ac3_critical_band_size_tab[j], end);
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for (k = i; k < end1; k++) {
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address = av_clip((psd[i] - v) >> 5, 0, 63);
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bap[i] = ff_ac3_bap_tab[address];
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i++;
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}
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} while (end > band_start_tab[j++]);
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}
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/* AC3 bit allocation. The algorithm is the one described in the AC3
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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, dba_values,
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mask);
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ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snr_offset, s->floor, 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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int i, j, k, l, v;
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/* compute bndtab and masktab from bandsz */
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k = 0;
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l = 0;
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for(i=0;i<50;i++) {
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band_start_tab[i] = l;
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v = ff_ac3_critical_band_size_tab[i];
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for(j=0;j<v;j++) bin_to_band_tab[k++]=i;
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l += v;
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}
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band_start_tab[50] = l;
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}
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