Merge pull request 'optimize_real_DFT' (#4) from optimize_real_DFT into master

Reviewed-on: #4

src/fourierTransformation.c

@@ -6,8 +6,6 @@
  */
 
 #include <math.h>
-#include <complex.h>
-
 #include "fourierTransformation.h"
 #include "globals.h"
 
@@ -20,18 +18,13 @@ void DFT(double x[SIG_LEN], double Xre[SIG_LEN], double Xim[SIG_LEN],
 	 * X_real, X_imag 	DFT of x (real and imaginary parts)
 	 * P 				power spectrum of x
 	 */
+	const float two_pi = 2 * M_PI / SIG_LEN;
 
-	int n, k;
-	for (k = 0; k < SIG_LEN; ++k) {
-		// Real part of X[k]
-		Xre[k] = 0;
-		for (n = 0; n < SIG_LEN; ++n) {
-			Xre[k] += x[n] * cos(n * k * PI2 / SIG_LEN);
-		}
-		// Imaginary part of X[k]
-		Xim[k] = 0;
-		for (n = 0; n < SIG_LEN; ++n) {
-			Xim[k] -= x[n] * sin(n * k * PI2 / SIG_LEN);
+	for (int k = 0; k < SIG_LEN; k++) {
+		Xre[k] = Xim[k] = 0;
+		for (int n = 0; n < SIG_LEN; n++) {
+			Xre[k] += x[n] * cos(n * k * two_pi);
+			Xim[k] -= x[n] * sin(n * k * two_pi);
 		}
 		// Power at kth frequency bin
 		P[k] = Xre[k] * Xre[k] + Xim[k] * Xim[k];

src/globals.h

@@ -8,6 +8,10 @@
 #ifndef GLOBALS_H_
 #define GLOBALS_H_
 
+#ifndef M_PI
+    #define M_PI 3.14159265358979323846
+#endif
+
 
 #define PI2 6.2832 //2*pi
 #define SIG_LEN 128 //signal length