1/**
2 * LPC utility code
3 * Copyright (c) 2006  Justin Ruggles <justin.ruggles@gmail.com>
4 *
5 * This file is part of Libav.
6 *
7 * Libav 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 * Libav 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 Libav; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22#include "libavutil/lls.h"
23
24#define LPC_USE_DOUBLE
25#include "lpc.h"
26
27
28/**
29 * Apply Welch window function to audio block
30 */
31static void lpc_apply_welch_window_c(const int32_t *data, int len,
32                                     double *w_data)
33{
34    int i, n2;
35    double w;
36    double c;
37
38    /* The optimization in commit fa4ed8c does not support odd len.
39     * If someone wants odd len extend that change. */
40    assert(!(len & 1));
41
42    n2 = (len >> 1);
43    c = 2.0 / (len - 1.0);
44
45    w_data+=n2;
46      data+=n2;
47    for(i=0; i<n2; i++) {
48        w = c - n2 + i;
49        w = 1.0 - (w * w);
50        w_data[-i-1] = data[-i-1] * w;
51        w_data[+i  ] = data[+i  ] * w;
52    }
53}
54
55/**
56 * Calculate autocorrelation data from audio samples
57 * A Welch window function is applied before calculation.
58 */
59static void lpc_compute_autocorr_c(const double *data, int len, int lag,
60                                   double *autoc)
61{
62    int i, j;
63
64    for(j=0; j<lag; j+=2){
65        double sum0 = 1.0, sum1 = 1.0;
66        for(i=j; i<len; i++){
67            sum0 += data[i] * data[i-j];
68            sum1 += data[i] * data[i-j-1];
69        }
70        autoc[j  ] = sum0;
71        autoc[j+1] = sum1;
72    }
73
74    if(j==lag){
75        double sum = 1.0;
76        for(i=j-1; i<len; i+=2){
77            sum += data[i  ] * data[i-j  ]
78                 + data[i+1] * data[i-j+1];
79        }
80        autoc[j] = sum;
81    }
82}
83
84/**
85 * Quantize LPC coefficients
86 */
87static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
88                               int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
89{
90    int i;
91    double cmax, error;
92    int32_t qmax;
93    int sh;
94
95    /* define maximum levels */
96    qmax = (1 << (precision - 1)) - 1;
97
98    /* find maximum coefficient value */
99    cmax = 0.0;
100    for(i=0; i<order; i++) {
101        cmax= FFMAX(cmax, fabs(lpc_in[i]));
102    }
103
104    /* if maximum value quantizes to zero, return all zeros */
105    if(cmax * (1 << max_shift) < 1.0) {
106        *shift = zero_shift;
107        memset(lpc_out, 0, sizeof(int32_t) * order);
108        return;
109    }
110
111    /* calculate level shift which scales max coeff to available bits */
112    sh = max_shift;
113    while((cmax * (1 << sh) > qmax) && (sh > 0)) {
114        sh--;
115    }
116
117    /* since negative shift values are unsupported in decoder, scale down
118       coefficients instead */
119    if(sh == 0 && cmax > qmax) {
120        double scale = ((double)qmax) / cmax;
121        for(i=0; i<order; i++) {
122            lpc_in[i] *= scale;
123        }
124    }
125
126    /* output quantized coefficients and level shift */
127    error=0;
128    for(i=0; i<order; i++) {
129        error -= lpc_in[i] * (1 << sh);
130        lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
131        error -= lpc_out[i];
132    }
133    *shift = sh;
134}
135
136static int estimate_best_order(double *ref, int min_order, int max_order)
137{
138    int i, est;
139
140    est = min_order;
141    for(i=max_order-1; i>=min_order-1; i--) {
142        if(ref[i] > 0.10) {
143            est = i+1;
144            break;
145        }
146    }
147    return est;
148}
149
150/**
151 * Calculate LPC coefficients for multiple orders
152 *
153 * @param lpc_type LPC method for determining coefficients,
154 *                 see #FFLPCType for details
155 */
156int ff_lpc_calc_coefs(LPCContext *s,
157                      const int32_t *samples, int blocksize, int min_order,
158                      int max_order, int precision,
159                      int32_t coefs[][MAX_LPC_ORDER], int *shift,
160                      enum FFLPCType lpc_type, int lpc_passes,
161                      int omethod, int max_shift, int zero_shift)
162{
163    double autoc[MAX_LPC_ORDER+1];
164    double ref[MAX_LPC_ORDER];
165    double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
166    int i, j, pass;
167    int opt_order;
168
169    assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER &&
170           lpc_type > FF_LPC_TYPE_FIXED);
171
172    /* reinit LPC context if parameters have changed */
173    if (blocksize != s->blocksize || max_order != s->max_order ||
174        lpc_type  != s->lpc_type) {
175        ff_lpc_end(s);
176        ff_lpc_init(s, blocksize, max_order, lpc_type);
177    }
178
179    if (lpc_type == FF_LPC_TYPE_LEVINSON) {
180        double *windowed_samples = s->windowed_samples + max_order;
181
182        s->lpc_apply_welch_window(samples, blocksize, windowed_samples);
183
184        s->lpc_compute_autocorr(windowed_samples, blocksize, max_order, autoc);
185
186        compute_lpc_coefs(autoc, max_order, &lpc[0][0], MAX_LPC_ORDER, 0, 1);
187
188        for(i=0; i<max_order; i++)
189            ref[i] = fabs(lpc[i][i]);
190    } else if (lpc_type == FF_LPC_TYPE_CHOLESKY) {
191        LLSModel m[2];
192        double var[MAX_LPC_ORDER+1], av_uninit(weight);
193
194        for(pass=0; pass<lpc_passes; pass++){
195            av_init_lls(&m[pass&1], max_order);
196
197            weight=0;
198            for(i=max_order; i<blocksize; i++){
199                for(j=0; j<=max_order; j++)
200                    var[j]= samples[i-j];
201
202                if(pass){
203                    double eval, inv, rinv;
204                    eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
205                    eval= (512>>pass) + fabs(eval - var[0]);
206                    inv = 1/eval;
207                    rinv = sqrt(inv);
208                    for(j=0; j<=max_order; j++)
209                        var[j] *= rinv;
210                    weight += inv;
211                }else
212                    weight++;
213
214                av_update_lls(&m[pass&1], var, 1.0);
215            }
216            av_solve_lls(&m[pass&1], 0.001, 0);
217        }
218
219        for(i=0; i<max_order; i++){
220            for(j=0; j<max_order; j++)
221                lpc[i][j]=-m[(pass-1)&1].coeff[i][j];
222            ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
223        }
224        for(i=max_order-1; i>0; i--)
225            ref[i] = ref[i-1] - ref[i];
226    }
227    opt_order = max_order;
228
229    if(omethod == ORDER_METHOD_EST) {
230        opt_order = estimate_best_order(ref, min_order, max_order);
231        i = opt_order-1;
232        quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
233    } else {
234        for(i=min_order-1; i<max_order; i++) {
235            quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
236        }
237    }
238
239    return opt_order;
240}
241
242av_cold int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
243                        enum FFLPCType lpc_type)
244{
245    s->blocksize = blocksize;
246    s->max_order = max_order;
247    s->lpc_type  = lpc_type;
248
249    if (lpc_type == FF_LPC_TYPE_LEVINSON) {
250        s->windowed_samples = av_mallocz((blocksize + max_order + 2) *
251                                         sizeof(*s->windowed_samples));
252        if (!s->windowed_samples)
253            return AVERROR(ENOMEM);
254    } else {
255        s->windowed_samples = NULL;
256    }
257
258    s->lpc_apply_welch_window = lpc_apply_welch_window_c;
259    s->lpc_compute_autocorr   = lpc_compute_autocorr_c;
260
261    if (HAVE_MMX)
262        ff_lpc_init_x86(s);
263
264    return 0;
265}
266
267av_cold void ff_lpc_end(LPCContext *s)
268{
269    av_freep(&s->windowed_samples);
270}
271