/*****************************************************************************/
/*random.c

Notes on usage :  

  1. In your main program add, 
	 extern  float rand1(void);
	 extern  float slete(float , float );

	
  2. From the main program call " slete(std, mean) "  where std, mean are the 
	 standard deviation, mean of the gaussian pdf respectively.

  3. The return value of slete(std, mean) is a gaussian random number.


/*****************************************************************************/
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#define PI      3.141592654


#define SEED1		29
#define SEED2		3191
#define SEED3		1987


static struct RandomNum
{
	int ix, iy, iz;
};

static struct RandomNum  random = { SEED1,SEED2,SEED3},*randptr = &random;

float rand1(void)
{
	int ixx, iyy, izz, itemp;
	float temp, uniform;

	ixx = randptr->ix/177;
	randptr->ix  = 171*(randptr->ix % 177) - 2*ixx;

	if ( randptr->ix < 0)
	{
		randptr->ix +=  30269;
	}
	iyy = randptr->iy/176;
	randptr->iy  = 172*(randptr->iy % 176) - 35*iyy;

	if ( randptr->iy < 0)
	{
		randptr->iy += 30307;
	}
	izz = randptr->iz/178;
	randptr->iz  = 170*(randptr->iz % 178) - 63*izz;

	if ( randptr->iz < 0)
	{
		randptr->iz += 30323;
	}

	temp = (float)randptr->ix/30269.0 + (float)randptr->iy/30307.0 +
				(float)randptr->iz/30323.0;
	itemp = (int)temp;

	uniform = temp - itemp;
	return(uniform);
}
/******************************************************************************/
	/* function slete() generates a gaussian random process by invoking
		rand1() and manipulating the sample returned by it. */
/******************************************************************************/
float slete(float std, float mean)
{
	float rand1(void);
	float gaussian, temp1, temp2;

	temp1 =  cos(2*PI*rand1());
	temp2 =  sqrt( -2.0 * log(rand1()));
	gaussian = mean +  std * temp1 * temp2;

	return(gaussian);
}
/***************************************************************************/