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libavcodec/lpc.c

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00001 
00022 #include "libavutil/lls.h"
00023 
00024 #define LPC_USE_DOUBLE
00025 #include "lpc.h"
00026 
00027 
00031 static void lpc_apply_welch_window_c(const int32_t *data, int len,
00032                                      double *w_data)
00033 {
00034     int i, n2;
00035     double w;
00036     double c;
00037 
00038     /* The optimization in commit fa4ed8c does not support odd len.
00039      * If someone wants odd len extend that change. */
00040     assert(!(len & 1));
00041 
00042     n2 = (len >> 1);
00043     c = 2.0 / (len - 1.0);
00044 
00045     w_data+=n2;
00046       data+=n2;
00047     for(i=0; i<n2; i++) {
00048         w = c - n2 + i;
00049         w = 1.0 - (w * w);
00050         w_data[-i-1] = data[-i-1] * w;
00051         w_data[+i  ] = data[+i  ] * w;
00052     }
00053 }
00054 
00059 static void lpc_compute_autocorr_c(const double *data, int len, int lag,
00060                                    double *autoc)
00061 {
00062     int i, j;
00063 
00064     for(j=0; j<lag; j+=2){
00065         double sum0 = 1.0, sum1 = 1.0;
00066         for(i=j; i<len; i++){
00067             sum0 += data[i] * data[i-j];
00068             sum1 += data[i] * data[i-j-1];
00069         }
00070         autoc[j  ] = sum0;
00071         autoc[j+1] = sum1;
00072     }
00073 
00074     if(j==lag){
00075         double sum = 1.0;
00076         for(i=j-1; i<len; i+=2){
00077             sum += data[i  ] * data[i-j  ]
00078                  + data[i+1] * data[i-j+1];
00079         }
00080         autoc[j] = sum;
00081     }
00082 }
00083 
00087 static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
00088                                int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
00089 {
00090     int i;
00091     double cmax, error;
00092     int32_t qmax;
00093     int sh;
00094 
00095     /* define maximum levels */
00096     qmax = (1 << (precision - 1)) - 1;
00097 
00098     /* find maximum coefficient value */
00099     cmax = 0.0;
00100     for(i=0; i<order; i++) {
00101         cmax= FFMAX(cmax, fabs(lpc_in[i]));
00102     }
00103 
00104     /* if maximum value quantizes to zero, return all zeros */
00105     if(cmax * (1 << max_shift) < 1.0) {
00106         *shift = zero_shift;
00107         memset(lpc_out, 0, sizeof(int32_t) * order);
00108         return;
00109     }
00110 
00111     /* calculate level shift which scales max coeff to available bits */
00112     sh = max_shift;
00113     while((cmax * (1 << sh) > qmax) && (sh > 0)) {
00114         sh--;
00115     }
00116 
00117     /* since negative shift values are unsupported in decoder, scale down
00118        coefficients instead */
00119     if(sh == 0 && cmax > qmax) {
00120         double scale = ((double)qmax) / cmax;
00121         for(i=0; i<order; i++) {
00122             lpc_in[i] *= scale;
00123         }
00124     }
00125 
00126     /* output quantized coefficients and level shift */
00127     error=0;
00128     for(i=0; i<order; i++) {
00129         error -= lpc_in[i] * (1 << sh);
00130         lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
00131         error -= lpc_out[i];
00132     }
00133     *shift = sh;
00134 }
00135 
00136 static int estimate_best_order(double *ref, int min_order, int max_order)
00137 {
00138     int i, est;
00139 
00140     est = min_order;
00141     for(i=max_order-1; i>=min_order-1; i--) {
00142         if(ref[i] > 0.10) {
00143             est = i+1;
00144             break;
00145         }
00146     }
00147     return est;
00148 }
00149 
00156 int ff_lpc_calc_coefs(LPCContext *s,
00157                       const int32_t *samples, int blocksize, int min_order,
00158                       int max_order, int precision,
00159                       int32_t coefs[][MAX_LPC_ORDER], int *shift,
00160                       enum FFLPCType lpc_type, int lpc_passes,
00161                       int omethod, int max_shift, int zero_shift)
00162 {
00163     double autoc[MAX_LPC_ORDER+1];
00164     double ref[MAX_LPC_ORDER];
00165     double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
00166     int i, j, pass;
00167     int opt_order;
00168 
00169     assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER &&
00170            lpc_type > FF_LPC_TYPE_FIXED);
00171 
00172     /* reinit LPC context if parameters have changed */
00173     if (blocksize != s->blocksize || max_order != s->max_order ||
00174         lpc_type  != s->lpc_type) {
00175         ff_lpc_end(s);
00176         ff_lpc_init(s, blocksize, max_order, lpc_type);
00177     }
00178 
00179     if (lpc_type == FF_LPC_TYPE_LEVINSON) {
00180         double *windowed_samples = s->windowed_samples + max_order;
00181 
00182         s->lpc_apply_welch_window(samples, blocksize, windowed_samples);
00183 
00184         s->lpc_compute_autocorr(windowed_samples, blocksize, max_order, autoc);
00185 
00186         compute_lpc_coefs(autoc, max_order, &lpc[0][0], MAX_LPC_ORDER, 0, 1);
00187 
00188         for(i=0; i<max_order; i++)
00189             ref[i] = fabs(lpc[i][i]);
00190     } else if (lpc_type == FF_LPC_TYPE_CHOLESKY) {
00191         LLSModel m[2];
00192         double var[MAX_LPC_ORDER+1], av_uninit(weight);
00193 
00194         for(pass=0; pass<lpc_passes; pass++){
00195             av_init_lls(&m[pass&1], max_order);
00196 
00197             weight=0;
00198             for(i=max_order; i<blocksize; i++){
00199                 for(j=0; j<=max_order; j++)
00200                     var[j]= samples[i-j];
00201 
00202                 if(pass){
00203                     double eval, inv, rinv;
00204                     eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
00205                     eval= (512>>pass) + fabs(eval - var[0]);
00206                     inv = 1/eval;
00207                     rinv = sqrt(inv);
00208                     for(j=0; j<=max_order; j++)
00209                         var[j] *= rinv;
00210                     weight += inv;
00211                 }else
00212                     weight++;
00213 
00214                 av_update_lls(&m[pass&1], var, 1.0);
00215             }
00216             av_solve_lls(&m[pass&1], 0.001, 0);
00217         }
00218 
00219         for(i=0; i<max_order; i++){
00220             for(j=0; j<max_order; j++)
00221                 lpc[i][j]=-m[(pass-1)&1].coeff[i][j];
00222             ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
00223         }
00224         for(i=max_order-1; i>0; i--)
00225             ref[i] = ref[i-1] - ref[i];
00226     }
00227     opt_order = max_order;
00228 
00229     if(omethod == ORDER_METHOD_EST) {
00230         opt_order = estimate_best_order(ref, min_order, max_order);
00231         i = opt_order-1;
00232         quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
00233     } else {
00234         for(i=min_order-1; i<max_order; i++) {
00235             quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
00236         }
00237     }
00238 
00239     return opt_order;
00240 }
00241 
00242 av_cold int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
00243                         enum FFLPCType lpc_type)
00244 {
00245     s->blocksize = blocksize;
00246     s->max_order = max_order;
00247     s->lpc_type  = lpc_type;
00248 
00249     if (lpc_type == FF_LPC_TYPE_LEVINSON) {
00250         s->windowed_samples = av_mallocz((blocksize + max_order + 2) *
00251                                          sizeof(*s->windowed_samples));
00252         if (!s->windowed_samples)
00253             return AVERROR(ENOMEM);
00254     } else {
00255         s->windowed_samples = NULL;
00256     }
00257 
00258     s->lpc_apply_welch_window = lpc_apply_welch_window_c;
00259     s->lpc_compute_autocorr   = lpc_compute_autocorr_c;
00260 
00261     if (HAVE_MMX)
00262         ff_lpc_init_x86(s);
00263 
00264     return 0;
00265 }
00266 
00267 av_cold void ff_lpc_end(LPCContext *s)
00268 {
00269     av_freep(&s->windowed_samples);
00270 }
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