// file: clpc_cal_5.cc
//
// this function computes the dft coefficients of a signal
//

// system include file
//
#include <stdio.h>
#include <math.h>

// local include file
//
#include "global_constants.h"
#include "calculate_lpc_constants.h"
#include "calculate_lpc.h"

// function: calculate_dft_cc
//
// arguments:
//    float**& dft_spect_coeffs_a: (output) buffer contains the dft of
//                                 the signal
//    float* signal_window_a: (input) buffer of signal
//    int samples_per_win_a: (input) number of samples per window
//    int num_chans_a: (input) number of channels
//    int dft_order_a: (input) type of window
//    int debug_mode_a: (input) debug level
//
// return: an int to indicate status
//
// this function calculates the dft of a signal using the equation below:
//   x(k) = sum ( x(n) * exp (-j * 2 * pi * k * n / N) ) n = 0 .. N-1
//
// where k is the current sample ranging from 0 .. N-1
// and N is the order of the DFT
//
//
int calculate_dft_cc (float**& dft_spect_coeffs_a, float* signal_window_a,
		      int samples_per_win_a, int num_chans_a, int dft_order_a,
		      int debug_mode_a) {

  int dft_samples = dft_order_a * num_chans_a;
  int signal_samples = samples_per_win_a * num_chans_a;
  
  float* temp_window = new float[dft_samples];

  // pad signal with 0s if dft order is larger than window
  //
  for (int sample = 0; sample < dft_samples; sample++) {
    if (sample < signal_samples) {
      temp_window[sample] = signal_window_a[sample];
    }
    else {
      temp_window[sample] = 0;
    }
  }
  
  for (int chan = 0; chan < num_chans_a; chan++) {
    for (int index = 0; index < dft_order_a; index++) {
      float twiddle_factor_rl = 0;
      float twiddle_factor_img = 0;
      int samp = 0;
      for (int sample = chan; sample < dft_samples; sample += num_chans_a) {
	float expn = 2.0 * M_PI * samp * index / dft_order_a;
	twiddle_factor_rl += temp_window[sample] * cos(expn);
	twiddle_factor_img -= temp_window[sample] * sin(expn);
	samp++;
      }
      dft_spect_coeffs_a[chan][index] = sqrt((twiddle_factor_rl *
	   twiddle_factor_rl) + (twiddle_factor_img * twiddle_factor_img));
    }
  }
  
  if (debug_mode_a > DEBUG_FULL) {
    for (int chan = 0; chan < num_chans_a; chan++) {
      for (int index = 0; index < dft_order_a; index++) {
	fprintf(stdout, "chan %d :: dft coeff [%d] =  %.6f\n",
		chan, index, dft_spect_coeffs_a[chan][index]);
      }
    }
    fprintf(stdout, "\n");
  }

  // delete scratch space
  //
  if (temp_window != (float*)NULL) {
    delete [] temp_window;
    temp_window = (float*)NULL;
  }
  
  // exit gracefully
  //
  return TRUE;
}