lpc.c
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1 
22 #include "libavutil/lls.h"
23 
24 #define LPC_USE_DOUBLE
25 #include "lpc.h"
26 
27 
31 static 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 
59 static 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 
87 static 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 
136 static 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 
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 
242 av_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 
260 
261  if (HAVE_MMX)
262  ff_lpc_init_x86(s);
263 
264  return 0;
265 }
266 
268 {
270 }