1 /*
2  * Common code between AC3 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 ac3.c
24  * Common code between AC3 encoder and decoder.
25  */
26 
27 #include "avcodec.h"
28 #include "ac3.h"
29 #include "bitstream.h"
30 
31 static uint8_t band_start_tab[51];
32 static uint8_t bin_to_band_tab[253];
33 
calc_lowcomp1(int a,int b0,int b1,int c)34 static 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 
calc_lowcomp(int a,int b0,int b1,int bin)44 static 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 
ff_ac3_bit_alloc_calc_psd(int8_t * exp,int start,int end,int16_t * psd,int16_t * band_psd)55 void 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 
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)83 void 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         band = 0;
160         for (seg = 0; seg < dba_nsegs; seg++) {
161             band += dba_offsets[seg];
162             if (dba_values[seg] >= 4) {
163                 delta = (dba_values[seg] - 3) << 7;
164             } else {
165                 delta = (dba_values[seg] - 4) << 7;
166             }
167             for (k = 0; k < dba_lengths[seg]; k++) {
168                 mask[band] += delta;
169                 band++;
170             }
171         }
172     }
173 }
174 
ff_ac3_bit_alloc_calc_bap(int16_t * mask,int16_t * psd,int start,int end,int snr_offset,int floor,uint8_t * bap)175 void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
176                                int snr_offset, int floor, uint8_t *bap)
177 {
178     int i, j, k, end1, v, address;
179 
180     /* special case, if snr offset is -960, set all bap's to zero */
181     if(snr_offset == -960) {
182         memset(bap, 0, 256);
183         return;
184     }
185 
186     i = start;
187     j = bin_to_band_tab[start];
188     do {
189         v = (FFMAX(mask[j] - snr_offset - floor, 0) & 0x1FE0) + floor;
190         end1 = FFMIN(band_start_tab[j] + ff_ac3_critical_band_size_tab[j], end);
191         for (k = i; k < end1; k++) {
192             address = av_clip((psd[i] - v) >> 5, 0, 63);
193             bap[i] = ff_ac3_bap_tab[address];
194             i++;
195         }
196     } while (end > band_start_tab[j++]);
197 }
198 
199 /* AC3 bit allocation. The algorithm is the one described in the AC3
200    spec. */
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)201 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
202                                    int8_t *exp, int start, int end,
203                                    int snr_offset, int fast_gain, int is_lfe,
204                                    int dba_mode, int dba_nsegs,
205                                    uint8_t *dba_offsets, uint8_t *dba_lengths,
206                                    uint8_t *dba_values)
207 {
208     int16_t psd[256];   /* scaled exponents */
209     int16_t band_psd[50]; /* interpolated exponents */
210     int16_t mask[50];   /* masking value */
211 
212     ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, band_psd);
213 
214     ff_ac3_bit_alloc_calc_mask(s, band_psd, start, end, fast_gain, is_lfe,
215                                dba_mode, dba_nsegs, dba_offsets, dba_lengths, dba_values,
216                                mask);
217 
218     ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snr_offset, s->floor, bap);
219 }
220 
221 /**
222  * Initializes some tables.
223  * note: This function must remain thread safe because it is called by the
224  *       AVParser init code.
225  */
ac3_common_init(void)226 av_cold void ac3_common_init(void)
227 {
228     int i, j, k, l, v;
229     /* compute bndtab and masktab from bandsz */
230     k = 0;
231     l = 0;
232     for(i=0;i<50;i++) {
233         band_start_tab[i] = l;
234         v = ff_ac3_critical_band_size_tab[i];
235         for(j=0;j<v;j++) bin_to_band_tab[k++]=i;
236         l += v;
237     }
238     band_start_tab[50] = l;
239 }
240