1 #include <math.h>
2 #include <stdlib.h>
3 #include "fec.h"
4
5 #define MAX_RANDOM 0x7fffffff
6
7 /* Generate gaussian random double with specified mean and std_dev */
normal_rand(double mean,double std_dev)8 double normal_rand(double mean, double std_dev)
9 {
10 double fac,rsq,v1,v2;
11 static double gset;
12 static int iset;
13
14 if(iset){
15 /* Already got one */
16 iset = 0;
17 return mean + std_dev*gset;
18 }
19 /* Generate two evenly distributed numbers between -1 and +1
20 * that are inside the unit circle
21 */
22 do {
23 v1 = 2.0 * (double)random() / MAX_RANDOM - 1;
24 v2 = 2.0 * (double)random() / MAX_RANDOM - 1;
25 rsq = v1*v1 + v2*v2;
26 } while(rsq >= 1.0 || rsq == 0.0);
27 fac = sqrt(-2.0*log(rsq)/rsq);
28 gset = v1*fac;
29 iset++;
30 return mean + std_dev*v2*fac;
31 }
32
addnoise(int sym,double amp,double gain,double offset,int clip)33 unsigned char addnoise(int sym,double amp,double gain,double offset,int clip){
34 int sample;
35
36 sample = offset + gain*normal_rand(sym?amp:-amp,1.0);
37 /* Clip to 8-bit offset range */
38 if(sample < 0)
39 sample = 0;
40 else if(sample > clip)
41 sample = clip;
42 return sample;
43 }
44