/* 
 * Simple dft
 * Nick Gamroth
 * May 2007
 */

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

#define PI 3.14159265

/* Returns n samples of a sine wave with f=1 */
double* sinegen(int n)
{
  int i;
  double *rval;
  double s;
  double d = 0.0;

  rval = malloc(n * sizeof(double));

  for(i = 0 ; i < n ; i++) {
    d = ((double)i) * PI / 180;
    rval[i] = sin(d);
  }
  return rval;
}

double* dft(int N, double* x)
{
  double Wk;
  int k, n;
  double *rval;

  rval = malloc(N * sizeof(double));

  for(k = 0 ; k < N - 1 ; k++) {
    Wk = (2 * PI * k) / N;
    for(n = 0 ; n < N - 1 ; n++) {
      rval[k] += x[n] * -1 * cos(n * Wk);
    }
  }

  return rval;
}

int main(int argc, char* argv)
{
  int n = 360;
  int N = 16;
  int i;
  double *signal, *freq;
  FILE *sig, *result;

  sig = fopen("signal.txt", "w");
  result = fopen("results.txt", "w");

  signal = sinegen(n);
  freq = dft(N, signal);
  for(i = 0 ; i < N ; i++) {
    //printf("%f\n", freq[i]);
    fprintf(result, "%f\n", freq[i]);
  }  
  for(i = 0 ; i < n ; i++) {
    fprintf(sig, "%f\n", signal[i]);
  }

  free(signal);
  fclose(result);
  fclose(sig);

  return 0;
}