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 */ 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 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
