1/*
2 * Common code between the AC-3 encoder and decoder
3 * Copyright (c) 2000 Fabrice Bellard
4 *
5 * This file is part of FFmpeg.
6 *
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22/**
23 * @file libavcodec/ac3.c
24 * Common code between the AC-3 encoder and decoder.
25 */
26
27#include "avcodec.h"
28#include "ac3.h"
29#include "bitstream.h"
30
31static uint8_t band_start_tab[51];
32static uint8_t bin_to_band_tab[253];
33
34static inline int calc_lowcomp1(int a, int b0, int b1, int c)
35{
36    if ((b0 + 256) == b1) {
37        a = c;
38    } else if (b0 > b1) {
39        a = FFMAX(a - 64, 0);
40    }
41    return a;
42}
43
44static inline int calc_lowcomp(int a, int b0, int b1, int bin)
45{
46    if (bin < 7) {
47        return calc_lowcomp1(a, b0, b1, 384);
48    } else if (bin < 20) {
49        return calc_lowcomp1(a, b0, b1, 320);
50    } else {
51        return FFMAX(a - 128, 0);
52    }
53}
54
55void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
56                               int16_t *band_psd)
57{
58    int bin, i, j, k, end1, v;
59
60    /* exponent mapping to PSD */
61    for(bin=start;bin<end;bin++) {
62        psd[bin]=(3072 - (exp[bin] << 7));
63    }
64
65    /* PSD integration */
66    j=start;
67    k=bin_to_band_tab[start];
68    do {
69        v=psd[j];
70        j++;
71        end1 = FFMIN(band_start_tab[k+1], end);
72        for(i=j;i<end1;i++) {
73            /* logadd */
74            int adr = FFMIN(FFABS(v - psd[j]) >> 1, 255);
75            v = FFMAX(v, psd[j]) + ff_ac3_log_add_tab[adr];
76            j++;
77        }
78        band_psd[k]=v;
79        k++;
80    } while (end > band_start_tab[k]);
81}
82
83int ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *band_psd,
84                               int start, int end, int fast_gain, int is_lfe,
85                               int dba_mode, int dba_nsegs, uint8_t *dba_offsets,
86                               uint8_t *dba_lengths, uint8_t *dba_values,
87                               int16_t *mask)
88{
89    int16_t excite[50]; /* excitation */
90    int bin, k;
91    int bndstrt, bndend, begin, end1, tmp;
92    int lowcomp, fastleak, slowleak;
93
94    /* excitation function */
95    bndstrt = bin_to_band_tab[start];
96    bndend = bin_to_band_tab[end-1] + 1;
97
98    if (bndstrt == 0) {
99        lowcomp = 0;
100        lowcomp = calc_lowcomp1(lowcomp, band_psd[0], band_psd[1], 384);
101        excite[0] = band_psd[0] - fast_gain - lowcomp;
102        lowcomp = calc_lowcomp1(lowcomp, band_psd[1], band_psd[2], 384);
103        excite[1] = band_psd[1] - fast_gain - lowcomp;
104        begin = 7;
105        for (bin = 2; bin < 7; bin++) {
106            if (!(is_lfe && bin == 6))
107                lowcomp = calc_lowcomp1(lowcomp, band_psd[bin], band_psd[bin+1], 384);
108            fastleak = band_psd[bin] - fast_gain;
109            slowleak = band_psd[bin] - s->slow_gain;
110            excite[bin] = fastleak - lowcomp;
111            if (!(is_lfe && bin == 6)) {
112                if (band_psd[bin] <= band_psd[bin+1]) {
113                    begin = bin + 1;
114                    break;
115                }
116            }
117        }
118
119        end1=bndend;
120        if (end1 > 22) end1=22;
121
122        for (bin = begin; bin < end1; bin++) {
123            if (!(is_lfe && bin == 6))
124                lowcomp = calc_lowcomp(lowcomp, band_psd[bin], band_psd[bin+1], bin);
125
126            fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain);
127            slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain);
128            excite[bin] = FFMAX(fastleak - lowcomp, slowleak);
129        }
130        begin = 22;
131    } else {
132        /* coupling channel */
133        begin = bndstrt;
134
135        fastleak = (s->cpl_fast_leak << 8) + 768;
136        slowleak = (s->cpl_slow_leak << 8) + 768;
137    }
138
139    for (bin = begin; bin < bndend; bin++) {
140        fastleak = FFMAX(fastleak - s->fast_decay, band_psd[bin] - fast_gain);
141        slowleak = FFMAX(slowleak - s->slow_decay, band_psd[bin] - s->slow_gain);
142        excite[bin] = FFMAX(fastleak, slowleak);
143    }
144
145    /* compute masking curve */
146
147    for (bin = bndstrt; bin < bndend; bin++) {
148        tmp = s->db_per_bit - band_psd[bin];
149        if (tmp > 0) {
150            excite[bin] += tmp >> 2;
151        }
152        mask[bin] = FFMAX(ff_ac3_hearing_threshold_tab[bin >> s->sr_shift][s->sr_code], excite[bin]);
153    }
154
155    /* delta bit allocation */
156
157    if (dba_mode == DBA_REUSE || dba_mode == DBA_NEW) {
158        int band, seg, delta;
159        if (dba_nsegs >= 8)
160            return -1;
161        band = 0;
162        for (seg = 0; seg < dba_nsegs; seg++) {
163            band += dba_offsets[seg];
164            if (band >= 50 || dba_lengths[seg] > 50-band)
165                return -1;
166            if (dba_values[seg] >= 4) {
167                delta = (dba_values[seg] - 3) << 7;
168            } else {
169                delta = (dba_values[seg] - 4) << 7;
170            }
171            for (k = 0; k < dba_lengths[seg]; k++) {
172                mask[band] += delta;
173                band++;
174            }
175        }
176    }
177    return 0;
178}
179
180void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
181                               int snr_offset, int floor,
182                               const uint8_t *bap_tab, uint8_t *bap)
183{
184    int i, j, k, end1, v, address;
185
186    /* special case, if snr offset is -960, set all bap's to zero */
187    if(snr_offset == -960) {
188        memset(bap, 0, 256);
189        return;
190    }
191
192    i = start;
193    j = bin_to_band_tab[start];
194    do {
195        v = (FFMAX(mask[j] - snr_offset - floor, 0) & 0x1FE0) + floor;
196        end1 = FFMIN(band_start_tab[j] + ff_ac3_critical_band_size_tab[j], end);
197        for (k = i; k < end1; k++) {
198            address = av_clip((psd[i] - v) >> 5, 0, 63);
199            bap[i] = bap_tab[address];
200            i++;
201        }
202    } while (end > band_start_tab[j++]);
203}
204
205/* AC-3 bit allocation. The algorithm is the one described in the AC-3
206   spec. */
207void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
208                                   int8_t *exp, int start, int end,
209                                   int snr_offset, int fast_gain, int is_lfe,
210                                   int dba_mode, int dba_nsegs,
211                                   uint8_t *dba_offsets, uint8_t *dba_lengths,
212                                   uint8_t *dba_values)
213{
214    int16_t psd[256];   /* scaled exponents */
215    int16_t band_psd[50]; /* interpolated exponents */
216    int16_t mask[50];   /* masking value */
217
218    ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, band_psd);
219
220    ff_ac3_bit_alloc_calc_mask(s, band_psd, start, end, fast_gain, is_lfe,
221                               dba_mode, dba_nsegs, dba_offsets, dba_lengths, dba_values,
222                               mask);
223
224    ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snr_offset, s->floor,
225                              ff_ac3_bap_tab, bap);
226}
227
228/**
229 * Initializes some tables.
230 * note: This function must remain thread safe because it is called by the
231 *       AVParser init code.
232 */
233av_cold void ac3_common_init(void)
234{
235    int i, j, k, l, v;
236    /* compute bndtab and masktab from bandsz */
237    k = 0;
238    l = 0;
239    for(i=0;i<50;i++) {
240        band_start_tab[i] = l;
241        v = ff_ac3_critical_band_size_tab[i];
242        for(j=0;j<v;j++) bin_to_band_tab[k++]=i;
243        l += v;
244    }
245    band_start_tab[50] = l;
246}
247