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  #ifdef HAVE_CONFIG_H
  #include "config.h"
  #endif
  
  #include "define.h"
  #include "main_FLP.h"
  #include "tuning_parameters.h"
  
  /* LPC analysis */
  void silk_find_LPC_FLP(
      silk_encoder_state              *psEncC,                            /* I/O  Encoder state                               */
      opus_int16                      NLSF_Q15[],                         /* O    NLSFs                                       */
      const silk_float                x[],                                /* I    Input signal                                */
      const silk_float                minInvGain                          /* I    Inverse of max prediction gain              */
  )
  {
      opus_int    k, subfr_length;
      silk_float  a[ MAX_LPC_ORDER ];
  
      /* Used only for NLSF interpolation */
      silk_float  res_nrg, res_nrg_2nd, res_nrg_interp;
      opus_int16  NLSF0_Q15[ MAX_LPC_ORDER ];
      silk_float  a_tmp[ MAX_LPC_ORDER ];
      silk_float  LPC_res[ MAX_FRAME_LENGTH + MAX_NB_SUBFR * MAX_LPC_ORDER ];
  
      subfr_length = psEncC->subfr_length + psEncC->predictLPCOrder;
  
      /* Default: No interpolation */
      psEncC->indices.NLSFInterpCoef_Q2 = 4;
  
      /* Burg AR analysis for the full frame */
      res_nrg = silk_burg_modified_FLP( a, x, minInvGain, subfr_length, psEncC->nb_subfr, psEncC->predictLPCOrder );
  
      if( psEncC->useInterpolatedNLSFs && !psEncC->first_frame_after_reset && psEncC->nb_subfr == MAX_NB_SUBFR ) {
          /* Optimal solution for last 10 ms; subtract residual energy here, as that's easier than        */
          /* adding it to the residual energy of the first 10 ms in each iteration of the search below    */
          res_nrg -= silk_burg_modified_FLP( a_tmp, x + ( MAX_NB_SUBFR / 2 ) * subfr_length, minInvGain, subfr_length, MAX_NB_SUBFR / 2, psEncC->predictLPCOrder );
  
          /* Convert to NLSFs */
          silk_A2NLSF_FLP( NLSF_Q15, a_tmp, psEncC->predictLPCOrder );
  
          /* Search over interpolation indices to find the one with lowest residual energy */
          res_nrg_2nd = silk_float_MAX;
          for( k = 3; k >= 0; k-- ) {
              /* Interpolate NLSFs for first half */
              silk_interpolate( NLSF0_Q15, psEncC->prev_NLSFq_Q15, NLSF_Q15, k, psEncC->predictLPCOrder );
  
              /* Convert to LPC for residual energy evaluation */
              silk_NLSF2A_FLP( a_tmp, NLSF0_Q15, psEncC->predictLPCOrder );
  
              /* Calculate residual energy with LSF interpolation */
              silk_LPC_analysis_filter_FLP( LPC_res, a_tmp, x, 2 * subfr_length, psEncC->predictLPCOrder );
              res_nrg_interp = (silk_float)(
                  silk_energy_FLP( LPC_res + psEncC->predictLPCOrder,                subfr_length - psEncC->predictLPCOrder ) +
                  silk_energy_FLP( LPC_res + psEncC->predictLPCOrder + subfr_length, subfr_length - psEncC->predictLPCOrder ) );
  
              /* Determine whether current interpolated NLSFs are best so far */
              if( res_nrg_interp < res_nrg ) {
                  /* Interpolation has lower residual energy */
                  res_nrg = res_nrg_interp;
                  psEncC->indices.NLSFInterpCoef_Q2 = (opus_int8)k;
              } else if( res_nrg_interp > res_nrg_2nd ) {
                  /* No reason to continue iterating - residual energies will continue to climb */
                  break;
              }
              res_nrg_2nd = res_nrg_interp;
          }
      }
  
      if( psEncC->indices.NLSFInterpCoef_Q2 == 4 ) {
          /* NLSF interpolation is currently inactive, calculate NLSFs from full frame AR coefficients */
          silk_A2NLSF_FLP( NLSF_Q15, a, psEncC->predictLPCOrder );
      }
  
      silk_assert( psEncC->indices.NLSFInterpCoef_Q2 == 4 || 
          ( psEncC->useInterpolatedNLSFs && !psEncC->first_frame_after_reset && psEncC->nb_subfr == MAX_NB_SUBFR ) );
  }
  