2 * Common code between AC3 encoder and decoder
3 * Copyright (c) 2000 Fabrice Bellard.
5 * This file is part of FFmpeg.
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.
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.
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
24 * Common code between AC3 encoder and decoder.
31 static inline int calc_lowcomp1(int a, int b0, int b1, int c)
33 if ((b0 + 256) == b1) {
41 static inline int calc_lowcomp(int a, int b0, int b1, int bin)
44 return calc_lowcomp1(a, b0, b1, 384);
45 } else if (bin < 20) {
46 return calc_lowcomp1(a, b0, b1, 320);
48 return FFMAX(a - 128, 0);
52 /* AC3 bit allocation. The algorithm is the one described in the AC3
54 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
55 int8_t *exp, int start, int end,
56 int snroffset, int fgain, int is_lfe,
57 int deltbae,int deltnseg,
58 uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba)
60 int bin,i,j,k,end1,v,bndstrt,bndend,lowcomp,begin;
61 int fastleak,slowleak,address,tmp;
62 int16_t psd[256]; /* scaled exponents */
63 int16_t bndpsd[50]; /* interpolated exponents */
64 int16_t excite[50]; /* excitation */
65 int16_t mask[50]; /* masking value */
67 /* exponent mapping to PSD */
68 for(bin=start;bin<end;bin++) {
69 psd[bin]=(3072 - (exp[bin] << 7));
78 end1 = FFMIN(bndtab[k+1], end);
81 int adr = FFMIN(FFABS(v - psd[j]) >> 1, 255);
82 v = FFMAX(v, psd[j]) + latab[adr];
87 } while (end > bndtab[k]);
89 /* excitation function */
90 bndstrt = masktab[start];
91 bndend = masktab[end-1] + 1;
95 lowcomp = calc_lowcomp1(lowcomp, bndpsd[0], bndpsd[1], 384);
96 excite[0] = bndpsd[0] - fgain - lowcomp;
97 lowcomp = calc_lowcomp1(lowcomp, bndpsd[1], bndpsd[2], 384);
98 excite[1] = bndpsd[1] - fgain - lowcomp;
100 for (bin = 2; bin < 7; bin++) {
101 if (!(is_lfe && bin == 6))
102 lowcomp = calc_lowcomp1(lowcomp, bndpsd[bin], bndpsd[bin+1], 384);
103 fastleak = bndpsd[bin] - fgain;
104 slowleak = bndpsd[bin] - s->sgain;
105 excite[bin] = fastleak - lowcomp;
106 if (!(is_lfe && bin == 6)) {
107 if (bndpsd[bin] <= bndpsd[bin+1]) {
115 if (end1 > 22) end1=22;
117 for (bin = begin; bin < end1; bin++) {
118 if (!(is_lfe && bin == 6))
119 lowcomp = calc_lowcomp(lowcomp, bndpsd[bin], bndpsd[bin+1], bin);
121 fastleak = FFMAX(fastleak - s->fdecay, bndpsd[bin] - fgain);
122 slowleak = FFMAX(slowleak - s->sdecay, bndpsd[bin] - s->sgain);
123 excite[bin] = FFMAX(fastleak - lowcomp, slowleak);
127 /* coupling channel */
130 fastleak = (s->cplfleak << 8) + 768;
131 slowleak = (s->cplsleak << 8) + 768;
134 for (bin = begin; bin < bndend; bin++) {
135 fastleak = FFMAX(fastleak - s->fdecay, bndpsd[bin] - fgain);
136 slowleak = FFMAX(slowleak - s->sdecay, bndpsd[bin] - s->sgain);
137 excite[bin] = FFMAX(fastleak, slowleak);
140 /* compute masking curve */
142 for (bin = bndstrt; bin < bndend; bin++) {
143 tmp = s->dbknee - bndpsd[bin];
145 excite[bin] += tmp >> 2;
147 mask[bin] = FFMAX(hth[bin >> s->halfratecod][s->fscod], excite[bin]);
150 /* delta bit allocation */
152 if (deltbae == 0 || deltbae == 1) {
153 int band, seg, delta;
155 for (seg = 0; seg < deltnseg; seg++) {
156 band += deltoffst[seg];
157 if (deltba[seg] >= 4) {
158 delta = (deltba[seg] - 3) << 7;
160 delta = (deltba[seg] - 4) << 7;
162 for (k = 0; k < deltlen[seg]; k++) {
169 /* compute bit allocation */
174 v = (FFMAX(mask[j] - snroffset - s->floor, 0) & 0x1FE0) + s->floor;
175 end1 = FFMIN(bndtab[j] + bndsz[j], end);
176 for (k = i; k < end1; k++) {
177 address = av_clip((psd[i] - v) >> 5, 0, 63);
178 bap[i] = baptab[address];
181 } while (end > bndtab[j++]);
184 void ac3_common_init(void)
187 /* compute bndtab and masktab from bandsz */
193 for(j=0;j<v;j++) masktab[k++]=i;