/* * Common code between AC3 encoder and decoder * Copyright (c) 2000 Fabrice Bellard. * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA *//** * @file ac3.c * Common code between AC3 encoder and decoder. */#include "avcodec.h"#include "ac3.h"#include "bitstream.h"static uint8_t band_start_tab[51];static uint8_t bin_to_band_tab[253];static inline int calc_lowcomp1(int a, int b0, int b1, int c){    if ((b0 + 256) == b1) {        a = c;    } else if (b0 > b1) {        a = FFMAX(a - 64, 0);    }    return a;}static inline int calc_lowcomp(int a, int b0, int b1, int bin){    if (bin < 7) {        return calc_lowcomp1(a, b0, b1, 384);    } else if (bin < 20) {        return calc_lowcomp1(a, b0, b1, 320);    } else {        return FFMAX(a - 128, 0);    }}void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,                               int16_t *band_psd){    int bin, i, j, k, end1, v;    /* exponent mapping to PSD */    for(bin=start;bin<end;bin++) {        psd[bin]=(3072 - (exp[bin] << 7));    }    /* PSD integration */    j=start;    k=bin_to_band_tab[start];    do {        v=psd[j];        j++;        end1 = FFMIN(band_start_tab[k+1], end);        for(i=j;i<end1;i++) {            /* logadd */            int adr = FFMIN(FFABS(v - psd[j]) >> 1, 255);            v = FFMAX(v, psd[j]) + ff_ac3_log_add_tab[adr];            j++;        }        band_psd[k]=v;        k++;    } while (end > band_start_tab[k]);}void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,                                int start, int end, int fast_gain, int is_lfe,                                int dba_mode, int dba_nsegs, uint8_t *dba_offsets,                                uint8_t *dba_lengths, uint8_t *dba_values,                                int16_t *mask){    int16_t excite[50]; /* excitation */    int bin, k;    int bndstrt, bndend, begin, end1, tmp;    int lowcomp, fastleak, slowleak;    /* excitation function */    bndstrt = bin_to_band_tab[start];    bndend = bin_to_band_tab[end-1] + 1;    if (bndstrt == 0) {        lowcomp = 0;        lowcomp = calc_lowcomp1(lowcomp, band_psd[0], band_psd[1], 384);        excite[0] = band_psd[0] - fast_gain - lowcomp;        lowcomp = calc_lowcomp1(lowcomp, band_psd[1], band_psd[2], 384);        excite[1] = band_psd[1] - fast_gain - lowcomp;        begin = 7;        for (bin = 2; bin < 7; bin++) {            if (!(is_lfe && bin == 6))                lowcomp = calc_lowcomp1(lowcomp, band_psd[bin], band_psd[bin+1], 384);            fastleak = band_psd[bin] - fast_gain;            slowleak = band_psd[bin] - s->slow_gain;            excite[bin] = fastleak - lowcomp;            if (!(is_lfe && bin == 6)) {                if (band_psd[bin] <= band_psd[bin+1]) {                    begin = bin + 1;                    break;                }            }        }        end1=bndend;        if (end1 > 22) end1=22;        for (bin = begin; bin < end1; bin++) {            if (!(is_lfe && bin == 6))                lowcomp = calc_lowcomp(lowcomp, band_psd[bin], band_psd[bin+1], bin);            fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain);            slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain);            excite[bin] = FFMAX(fastleak - lowcomp, slowleak);        }        begin = 22;    } else {        /* coupling channel */        begin = bndstrt;        fastleak = (s->cpl_fast_leak << 8) + 768;        slowleak = (s->cpl_slow_leak << 8) + 768;    }    for (bin = begin; bin < bndend; bin++) {        fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain);        slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain);        excite[bin] = FFMAX(fastleak, slowleak);    }    /* compute masking curve */    for (bin = bndstrt; bin < bndend; bin++) {        tmp = s->db_per_bit - band_psd[bin];        if (tmp > 0) {            excite[bin] += tmp >> 2;        }        mask[bin] = FFMAX(ff_ac3_hearing_threshold_tab[bin >> s->sr_shift][s->sr_code], excite[bin]);    }    /* delta bit allocation */    if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) {        int band, seg, delta;        band = 0;        for (seg = 0; seg < FFMIN(8, dba_nsegs); seg++) {            band = FFMIN(49, band + dba_offsets[seg]);            if (dba_values[seg] >= 4) {                delta = (dba_values[seg] - 3) << 7;            } else {                delta = (dba_values[seg] - 4) << 7;            }            for (k = 0; k < dba_lengths[seg]; k++) {                mask[band] += delta;                band++;            }        }    }}void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,                               int snr_offset, int floor,                               const uint8_t *bap_tab, uint8_t *bap){    int i, j, k, end1, v, address;    /* special case, if snr offset is -960, set all bap's to zero */    if(snr_offset == -960) {        memset(bap, 0, 256);        return;    }    i = start;    j = bin_to_band_tab[start];    do {        v = (FFMAX(mask[j] - snr_offset - floor, 0) & 0x1FE0) + floor;        end1 = FFMIN(band_start_tab[j] + ff_ac3_critical_band_size_tab[j], end);        for (k = i; k < end1; k++) {            address = av_clip((psd[i] - v) >> 5, 0, 63);            bap[i] = bap_tab[address];            i++;        }    } while (end > band_start_tab[j++]);}/* AC3 bit allocation. The algorithm is the one described in the AC3   spec. */void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,                                   int8_t *exp, int start, int end,                                   int snr_offset, int fast_gain, int is_lfe,                                   int dba_mode, int dba_nsegs,                                   uint8_t *dba_offsets, uint8_t *dba_lengths,                                   uint8_t *dba_values){    int16_t psd[256];   /* scaled exponents */    int16_t band_psd[50]; /* interpolated exponents */    int16_t mask[50];   /* masking value */    ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, band_psd);    ff_ac3_bit_alloc_calc_mask(s, band_psd, start, end, fast_gain, is_lfe,                               dba_mode, dba_nsegs, dba_offsets, dba_lengths, dba_values,                               mask);    ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snr_offset, s->floor,                              ff_ac3_bap_tab, bap);}/** * Initializes some tables. * note: This function must remain thread safe because it is called by the *       AVParser init code. */av_cold void ac3_common_init(void){    int i, j, k, l, v;    /* compute bndtab and masktab from bandsz */    k = 0;    l = 0;    for(i=0;i<50;i++) {        band_start_tab[i] = l;        v = ff_ac3_critical_band_size_tab[i];        for(j=0;j<v;j++) bin_to_band_tab[k++]=i;        l += v;    }    band_start_tab[50] = l;}