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  #ifdef OPUS_HAVE_CONFIG_H
  #include "opus_config.h"
  #endif
  
  #include "SigProc_FLP.h"
  #include "tuning_parameters.h"
  #include "define.h"
  
  #define MAX_FRAME_SIZE              384 /* subfr_length * nb_subfr = ( 0.005 * 16000 + 16 ) * 4 = 384*/
  
  /* Compute reflection coefficients from input signal */
  silk_float silk_burg_modified_FLP(          /* O    returns residual energy                                     */
      silk_float          A[],                /* O    prediction coefficients (length order)                      */
      const silk_float    x[],                /* I    input signal, length: nb_subfr*(D+L_sub)                    */
      const silk_float    minInvGain,         /* I    minimum inverse prediction gain                             */
      const opus_int      subfr_length,       /* I    input signal subframe length (incl. D preceding samples)    */
      const opus_int      nb_subfr,           /* I    number of subframes stacked in x                            */
      const opus_int      D                   /* I    order                                                       */
  )
  {
      opus_int         k, n, s, reached_max_gain;
      double           C0, invGain, num, nrg_f, nrg_b, rc, Atmp, tmp1, tmp2;
      const silk_float *x_ptr;
      double           C_first_row[ SILK_MAX_ORDER_LPC ], C_last_row[ SILK_MAX_ORDER_LPC ];
      double           CAf[ SILK_MAX_ORDER_LPC + 1 ], CAb[ SILK_MAX_ORDER_LPC + 1 ];
      double           Af[ SILK_MAX_ORDER_LPC ];
  
      silk_assert( subfr_length * nb_subfr <= MAX_FRAME_SIZE );
  
      /* Compute autocorrelations, added over subframes */
      C0 = silk_energy_FLP( x, nb_subfr * subfr_length );
      silk_memset( C_first_row, 0, SILK_MAX_ORDER_LPC * sizeof( double ) );
      for( s = 0; s < nb_subfr; s++ ) {
          x_ptr = x + s * subfr_length;
          for( n = 1; n < D + 1; n++ ) {
              C_first_row[ n - 1 ] += silk_inner_product_FLP( x_ptr, x_ptr + n, subfr_length - n );
          }
      }
      silk_memcpy( C_last_row, C_first_row, SILK_MAX_ORDER_LPC * sizeof( double ) );
  
      /* Initialize */
      CAb[ 0 ] = CAf[ 0 ] = C0 + FIND_LPC_COND_FAC * C0 + 1e-9f;
      invGain = 1.0f;
      reached_max_gain = 0;
      for( n = 0; n < D; n++ ) {
          /* Update first row of correlation matrix (without first element) */
          /* Update last row of correlation matrix (without last element, stored in reversed order) */
          /* Update C * Af */
          /* Update C * flipud(Af) (stored in reversed order) */
          for( s = 0; s < nb_subfr; s++ ) {
              x_ptr = x + s * subfr_length;
              tmp1 = x_ptr[ n ];
              tmp2 = x_ptr[ subfr_length - n - 1 ];
              for( k = 0; k < n; k++ ) {
                  C_first_row[ k ] -= x_ptr[ n ] * x_ptr[ n - k - 1 ];
                  C_last_row[ k ]  -= x_ptr[ subfr_length - n - 1 ] * x_ptr[ subfr_length - n + k ];
                  Atmp = Af[ k ];
                  tmp1 += x_ptr[ n - k - 1 ] * Atmp;
                  tmp2 += x_ptr[ subfr_length - n + k ] * Atmp;
              }
              for( k = 0; k <= n; k++ ) {
                  CAf[ k ] -= tmp1 * x_ptr[ n - k ];
                  CAb[ k ] -= tmp2 * x_ptr[ subfr_length - n + k - 1 ];
              }
          }
          tmp1 = C_first_row[ n ];
          tmp2 = C_last_row[ n ];
          for( k = 0; k < n; k++ ) {
              Atmp = Af[ k ];
              tmp1 += C_last_row[  n - k - 1 ] * Atmp;
              tmp2 += C_first_row[ n - k - 1 ] * Atmp;
          }
          CAf[ n + 1 ] = tmp1;
          CAb[ n + 1 ] = tmp2;
  
          /* Calculate nominator and denominator for the next order reflection (parcor) coefficient */
          num = CAb[ n + 1 ];
          nrg_b = CAb[ 0 ];
          nrg_f = CAf[ 0 ];
          for( k = 0; k < n; k++ ) {
              Atmp = Af[ k ];
              num   += CAb[ n - k ] * Atmp;
              nrg_b += CAb[ k + 1 ] * Atmp;
              nrg_f += CAf[ k + 1 ] * Atmp;
          }
          silk_assert( nrg_f > 0.0 );
          silk_assert( nrg_b > 0.0 );
  
          /* Calculate the next order reflection (parcor) coefficient */
          rc = -2.0 * num / ( nrg_f + nrg_b );
          silk_assert( rc > -1.0 && rc < 1.0 );
  
          /* Update inverse prediction gain */
          tmp1 = invGain * ( 1.0 - rc * rc );
          if( tmp1 <= minInvGain ) {
              /* Max prediction gain exceeded; set reflection coefficient such that max prediction gain is exactly hit */
              rc = sqrt( 1.0 - minInvGain / invGain );
              if( num > 0 ) {
                  /* Ensure adjusted reflection coefficients has the original sign */
                  rc = -rc;
              }
              invGain = minInvGain;
              reached_max_gain = 1;
          } else {
              invGain = tmp1;
          }
  
          /* Update the AR coefficients */
          for( k = 0; k < (n + 1) >> 1; k++ ) {
              tmp1 = Af[ k ];
              tmp2 = Af[ n - k - 1 ];
              Af[ k ]         = tmp1 + rc * tmp2;
              Af[ n - k - 1 ] = tmp2 + rc * tmp1;
          }
          Af[ n ] = rc;
  
          if( reached_max_gain ) {
              /* Reached max prediction gain; set remaining coefficients to zero and exit loop */
              for( k = n + 1; k < D; k++ ) {
                  Af[ k ] = 0.0;
              }
              break;
          }
  
          /* Update C * Af and C * Ab */
          for( k = 0; k <= n + 1; k++ ) {
              tmp1 = CAf[ k ];
              CAf[ k ]          += rc * CAb[ n - k + 1 ];
              CAb[ n - k + 1  ] += rc * tmp1;
          }
      }
  
      if( reached_max_gain ) {
          /* Convert to silk_float */
          for( k = 0; k < D; k++ ) {
              A[ k ] = (silk_float)( -Af[ k ] );
          }
          /* Subtract energy of preceding samples from C0 */
          for( s = 0; s < nb_subfr; s++ ) {
              C0 -= silk_energy_FLP( x + s * subfr_length, D );
          }
          /* Approximate residual energy */
          nrg_f = C0 * invGain;
      } else {
          /* Compute residual energy and store coefficients as silk_float */
          nrg_f = CAf[ 0 ];
          tmp1 = 1.0;
          for( k = 0; k < D; k++ ) {
              Atmp = Af[ k ];
              nrg_f += CAf[ k + 1 ] * Atmp;
              tmp1  += Atmp * Atmp;
              A[ k ] = (silk_float)(-Atmp);
          }
          nrg_f -= FIND_LPC_COND_FAC * C0 * tmp1;
      }
  
      /* Return residual energy */
      return (silk_float)nrg_f;
  }
  