// file: $SPEECH_HOMEWORK4/hw4/class/snr_ratio/v1.0/snr_lp_1.cc
//

// isip include files
//
#include <string.h>
#include <math.h>
#include "signal_noise_ratio.h"
#include "signal_noise_ratio_constants.h"
#include <integral.h>
#include <integral_constants.h>

// method: calculate_lp_pred_cc
//
// arguments:
//
// return: a logical_1 indicating status
//
logical_1 Signal::calculate_lp_pred_cc(float_4**& lp_pred_a,
				       float_4** auto_corr_values_a,
				       float_4*& lp_gain_a) {

  // define variables to store reflection and the previous predictor
  // coefficients
  //
  float_4* reflect = new float_4[lp_order_d + 1];
  float_4* prev = new float_4[lp_order_d + 1];
  float_4 lp_error;

  // loop over each channel
  //
  for (int_4 i=0; i<num_chans_d; i++) {

    // reset buffers
    //
    memset(reflect, 0, sizeof(float_4) * (lp_order_d + 1));
    memset(prev, 0, sizeof(float_4) * (lp_order_d + 1));
    lp_error = auto_corr_values_a[i][0];

    for (int_4 j=1; j<=lp_order_d; j++) {

      reflect[j] = 0;

      for (int_4 k=1; k<j; k++) 
	reflect[j] -= prev[k] * auto_corr_values_a[i][j-k];

      reflect[j] -= auto_corr_values_a[i][j];
      reflect[j] /= lp_error;

      // update lp_pred_a
      //
      lp_pred_a[i][j] = reflect[j];
      for (int_4 k=1; k<j; k++)
	lp_pred_a[i][k] = prev[k] + reflect[j] * prev[j-k];

      // update lp_error
      //
      lp_error *= (float_4)1.0 - reflect[j] * reflect[j];
      
      // update prev
      //
      for (int_4 k=1; k<=j; k++)
	prev[k] = lp_pred_a[i][k];
    }

    // invert the lp_pred
    //
    for (int_4 j=1; j<= lp_order_d; j++) {
      lp_pred_a[i][j] *= -1;
    }

    // update the gain value
    //
    lp_gain_a[i] = lp_error;
  }

  if (debug_level_d > 1) {
    for (int_4 i = 0; i < num_chans_d; i++) {
      for (int_4 j = 0; j <= lp_order_d; j++) {
        fprintf(stdout, "chan %ld :: lp_pred values [%ld] =  %.6f\n",
                i, j, lp_pred_a[i][j]);
      }
    }
    fprintf(stdout, "\n");
  }

  
  delete [] reflect;
  delete [] prev;

  // exit gracefully
  //
  return ISIP_TRUE;
  
}