text: /**
   * LPC utility code
   * Copyright (c) 2006  Justin Ruggles <justin.ruggles@gmail.com>
   *
   * This file is part of Libav.
   *
   * Libav is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * Libav is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with Libav; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
   */
  
  #include "libavutil/lls.h"
  
  #define LPC_USE_DOUBLE
  #include "lpc.h"
  
  
  /**
   * Apply Welch window function to audio block
   */
  static void lpc_apply_welch_window_c(const int32_t *data, int len,
                                       double *w_data)
  {
      int i, n2;
      double w;
      double c;
  
      /* The optimization in commit fa4ed8c does not support odd len.
       * If someone wants odd len extend that change. */
      assert(!(len & 1));
  
      n2 = (len >> 1);
      c = 2.0 / (len - 1.0);
  
      w_data+=n2;
        data+=n2;
      for(i=0; i<n2; i++) {
          w = c - n2 + i;
          w = 1.0 - (w * w);
          w_data[-i-1] = data[-i-1] * w;
          w_data[+i  ] = data[+i  ] * w;
      }
  }
  
  /**
   * Calculate autocorrelation data from audio samples
   * A Welch window function is applied before calculation.
   */
  static void lpc_compute_autocorr_c(const double *data, int len, int lag,
                                     double *autoc)
  {
      int i, j;
  
      for(j=0; j<lag; j+=2){
          double sum0 = 1.0, sum1 = 1.0;
          for(i=j; i<len; i++){
              sum0 += data[i] * data[i-j];
              sum1 += data[i] * data[i-j-1];
          }
          autoc[j  ] = sum0;
          autoc[j+1] = sum1;
      }
  
      if(j==lag){
          double sum = 1.0;
          for(i=j-1; i<len; i+=2){
              sum += data[i  ] * data[i-j  ]
                   + data[i+1] * data[i-j+1];
          }
          autoc[j] = sum;
      }
  }
  
  /**
   * Quantize LPC coefficients
   */
  static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
                                 int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
  {
      int i;
      double cmax, error;
      int32_t qmax;
      int sh;
  
      /* define maximum levels */
      qmax = (1 << (precision - 1)) - 1;
  
      /* find maximum coefficient value */
      cmax = 0.0;
      for(i=0; i<order; i++) {
          cmax= FFMAX(cmax, fabs(lpc_in[i]));
      }
  
      /* if maximum value quantizes to zero, return all zeros */
      if(cmax * (1 << max_shift) < 1.0) {
          *shift = zero_shift;
          memset(lpc_out, 0, sizeof(int32_t) * order);
          return;
      }
  
      /* calculate level shift which scales max coeff to available bits */
      sh = max_shift;
      while((cmax * (1 << sh) > qmax) && (sh > 0)) {
          sh--;
      }
  
      /* since negative shift values are unsupported in decoder, scale down
         coefficients instead */
      if(sh == 0 && cmax > qmax) {
          double scale = ((double)qmax) / cmax;
          for(i=0; i<order; i++) {
              lpc_in[i] *= scale;
          }
      }
  
      /* output quantized coefficients and level shift */
      error=0;
      for(i=0; i<order; i++) {
          error -= lpc_in[i] * (1 << sh);
          lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
          error -= lpc_out[i];
      }
      *shift = sh;
  }
  
  static int estimate_best_order(double *ref, int min_order, int max_order)
  {
      int i, est;
  
      est = min_order;
      for(i=max_order-1; i>=min_order-1; i--) {
          if(ref[i] > 0.10) {
              est = i+1;
              break;
          }
      }
      return est;
  }
  
  /**
   * Calculate LPC coefficients for multiple orders
   *
   * @param lpc_type LPC method for determining coefficients,
   *                 see #FFLPCType for details
   */
  int ff_lpc_calc_coefs(LPCContext *s,
                        const int32_t *samples, int blocksize, int min_order,
                        int max_order, int precision,
                        int32_t coefs[][MAX_LPC_ORDER], int *shift,
                        enum FFLPCType lpc_type, int lpc_passes,
                        int omethod, int max_shift, int zero_shift)
  {
      double autoc[MAX_LPC_ORDER+1];
      double ref[MAX_LPC_ORDER];
      double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
      int i, j, pass;
      int opt_order;
  
      assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER &&
             lpc_type > FF_LPC_TYPE_FIXED);
  
      /* reinit LPC context if parameters have changed */
      if (blocksize != s->blocksize || max_order != s->max_order ||
          lpc_type  != s->lpc_type) {
          ff_lpc_end(s);
          ff_lpc_init(s, blocksize, max_order, lpc_type);
      }
  
      if (lpc_type == FF_LPC_TYPE_LEVINSON) {
          double *windowed_samples = s->windowed_samples + max_order;
  
          s->lpc_apply_welch_window(samples, blocksize, windowed_samples);
  
          s->lpc_compute_autocorr(windowed_samples, blocksize, max_order, autoc);
  
          compute_lpc_coefs(autoc, max_order, &lpc[0][0], MAX_LPC_ORDER, 0, 1);
  
          for(i=0; i<max_order; i++)
              ref[i] = fabs(lpc[i][i]);
      } else if (lpc_type == FF_LPC_TYPE_CHOLESKY) {
          LLSModel m[2];
          double var[MAX_LPC_ORDER+1], av_uninit(weight);
  
          for(pass=0; pass<lpc_passes; pass++){
              av_init_lls(&m[pass&1], max_order);
  
              weight=0;
              for(i=max_order; i<blocksize; i++){
                  for(j=0; j<=max_order; j++)
                      var[j]= samples[i-j];
  
                  if(pass){
                      double eval, inv, rinv;
                      eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
                      eval= (512>>pass) + fabs(eval - var[0]);
                      inv = 1/eval;
                      rinv = sqrt(inv);
                      for(j=0; j<=max_order; j++)
                          var[j] *= rinv;
                      weight += inv;
                  }else
                      weight++;
  
                  av_update_lls(&m[pass&1], var, 1.0);
              }
              av_solve_lls(&m[pass&1], 0.001, 0);
          }
  
          for(i=0; i<max_order; i++){
              for(j=0; j<max_order; j++)
                  lpc[i][j]=-m[(pass-1)&1].coeff[i][j];
              ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
          }
          for(i=max_order-1; i>0; i--)
              ref[i] = ref[i-1] - ref[i];
      }
      opt_order = max_order;
  
      if(omethod == ORDER_METHOD_EST) {
          opt_order = estimate_best_order(ref, min_order, max_order);
          i = opt_order-1;
          quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
      } else {
          for(i=min_order-1; i<max_order; i++) {
              quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
          }
      }
  
      return opt_order;
  }
  
  av_cold int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
                          enum FFLPCType lpc_type)
  {
      s->blocksize = blocksize;
      s->max_order = max_order;
      s->lpc_type  = lpc_type;
  
      if (lpc_type == FF_LPC_TYPE_LEVINSON) {
          s->windowed_samples = av_mallocz((blocksize + max_order + 2) *
                                           sizeof(*s->windowed_samples));
          if (!s->windowed_samples)
              return AVERROR(ENOMEM);
      } else {
          s->windowed_samples = NULL;
      }
  
      s->lpc_apply_welch_window = lpc_apply_welch_window_c;
      s->lpc_compute_autocorr   = lpc_compute_autocorr_c;
  
      if (HAVE_MMX)
          ff_lpc_init_x86(s);
  
      return 0;
  }
  
  av_cold void ff_lpc_end(LPCContext *s)
  {
      av_freep(&s->windowed_samples);
  }
  