init commit

sim.c

@@ -0,0 +1,43 @@
+#include <math.h>
+#include <stdlib.h>
+#include "fec.h"
+
+#define	MAX_RANDOM	0x7fffffff
+
+/* Generate gaussian random double with specified mean and std_dev */
+double normal_rand(double mean, double std_dev)
+{
+  double fac,rsq,v1,v2;
+  static double gset;
+  static int iset;
+
+  if(iset){
+    /* Already got one */
+    iset = 0;
+    return mean + std_dev*gset;
+  }
+  /* Generate two evenly distributed numbers between -1 and +1
+   * that are inside the unit circle
+   */
+  do {
+    v1 = 2.0 * (double)random() / MAX_RANDOM - 1;
+    v2 = 2.0 * (double)random() / MAX_RANDOM - 1;
+    rsq = v1*v1 + v2*v2;
+  } while(rsq >= 1.0 || rsq == 0.0);
+  fac = sqrt(-2.0*log(rsq)/rsq);
+  gset = v1*fac;
+  iset++;
+  return mean + std_dev*v2*fac;
+}
+
+unsigned char addnoise(int sym,double amp,double gain,double offset,int clip){
+  int sample;
+    
+  sample = offset + gain*normal_rand(sym?amp:-amp,1.0);
+  /* Clip to 8-bit offset range */
+  if(sample < 0)
+    sample = 0;
+  else if(sample > clip)
+    sample = clip;
+  return sample;
+}