// file: $ECE_8993/util/calculate_lpc/v1.0/clpc_comp_7.cc
//
// computes the lp predictor spectrum from the predictor coefficients
//

// system include files
//
#include <string.h>

// isip include files
//
#include <integral.h>
#include <integral_constants.h>

// local include files
//
#include "calculate_lpc.h"

#include "calculate_lpc_constants.h"

// function: compute_lp_spect_cc
//
// arguments:
//
//  float_4* pred_coeffs: (output) predictor coefficients
//  float_4* spect_coeffs: (output) spectrum coefficients
//  int_4 lp_order: (input) order of the lp model
//  int_4 num_samples: (input) number of samples
//  float_4 gain: (input) gain of the lp model to estimate the signal spectrum
//  
// return value: a logical_1 indicating status
//
// this function computes the spectrum given a set of  lp predictor
// and a gain value coefficients
//
logical_1 compute_lp_spect_cc(float_4* pred_coeffs_a, float_4* spect_coeffs_a,
			      int_4 lp_order_a, int_4 num_samples_a,
			      float_4 gain_a) {

  // loop over all spectrum components
  //
  for (int_4 i = (int_4)0; i < num_samples_a; i++) {

    // initialize the real and imaginary portions of the spectrum
    //
    float_4 real_part = (float_4)1.0;
    float_4 imag_part = (float_4)0.0;

    // loop over each of the predictor values
    //
    for (int_4 j = 1; j <= lp_order_a; j++) {

      real_part -= pred_coeffs_a[j] * cos((ISIP_TWOPI /
					   (float_4) num_samples_a) *
					  (float_4)((i * j) % num_samples_a));
      imag_part += pred_coeffs_a[j] * sin((ISIP_TWOPI /
					   (float_4) num_samples_a) *
					  (float_4)((i * j) % num_samples_a));
    }

    // save the magnitude of the spectrum
    //
    spect_coeffs_a[i] = sqrt(gain_a / ((real_part * real_part) +
				       (imag_part * imag_part)));

 } 

  // exit gracefully
  //
  return ISIP_TRUE;
}