random.c

介绍了ldpc编码相关的设计与实现

#include "random.h"

long s1,s2;

/*Generate a uniform random number between 0 and 1.*/
double random_source()
{
	long z,k;
	k = s1 / 53668L;
	s1 = 40014L * (s1 - k * 53668L) - k * 12211L;
	if(s1 < 0)
		s1 = s1 + 2147483563L;
	k = s2 / 52774;
	s2 = 40692L * (s2 - k * 52774L) - k * 3791L;
	if(s2 < 0)
		s2 = s2 + 2147483399L;
	z = s1 - s2;
	if(z < 1)
		z = z + 2147483562L;
	
	return (double) z / (double) 2147483563.0;
}

/*Generate a uniform random number between -1 and 1. */
double generate_random_source()
{
	double sign;
	if(random_source() >= 0.5)
		sign = -1.0;
	else
		sign = 1.0;
	return sign * random_source();
}

/*Generate a random number 0 and 1 with p0=p1=0.5.*/
short generate_binary_source()
{
	if(random_source() < 0.5)
		return 0;
	else
		return 1;
}

/*Generate a gaussian random with 0 mean sigma2 variance. */
double generate_gaussian_source(double sigma2)
{
	static int iset = 0;	/* It save the last value. */
	static double gset;
	double fac,r,v1,v2;
	
	if(iset == 0)
	{
		do
		{
			v1 = generate_random_source();
			v2 = generate_random_source();
			r = v1 * v1 + v2 * v2;
		}while(r >= 1.0 || r == 0.0);
		fac = sqrt(-2.0 * sigma2 * log(r) / r);
		gset = v1 * fac;
		iset = 1;
		return (double)(v2 * fac);
	}
	else
	{
		iset = 0;
		return (double)(gset);
	}
}