/*
 * rand.c: randomize(), urand(), irand(), erand(), grand()
 *
 * urand: returns uniform pseudo-random double in the range [0.0, 1.0)
 * irand: returns uniform pseudo-random integer in the range [1, n]
 * erand: returns exponentially distributed pseudo-random double with mean 1
 * grand: returns gaussian distributed double with mean 0 and variance 1
 *
 * Before the first call to any of these routines, the random seed should
 * be initialized directly using srand() or randomly using randomize().
 */

#include <stdio.h>
#include <time.h>
#include <math.h>
#include <stdlib.h>

/*
 * RAN macro returns pseudo-random double in the range [0.0, 1.0)
 */
#ifdef RAND_MAX
# define RAN  (rand()/( (double) RAND_MAX + 1))
#else
# define RAN  (rand()/2147483648.0)		/*  / 2**31  */
#endif

/*
 * randomize: initialize seed from time-of-day
 */
void randomize( void)
{
    srand( (unsigned) time( (time_t *) NULL) );
}

/*
 * urand: returns uniform pseudo-random double in the range [0.0, 1.0)
 */
double urand( void)
{
    return RAN;
}

/*
 * irand: returns uniform pseudo-random integer in the range [1, n]
 */
int irand( int n)
{
    return 1 + (int) (n * RAN);
}

/*
 * erand: returns exponentially distributed pseudo-random double with mean 1
 */
double erand( void)
{
    return  -log(1.0 - RAN);
}

/*
 * grand: returns gaussian distributed pseudo-random double
 *	  with mean 0 and variance 1
 */
double grand( void)
{
    int i;
    double r = -6.0;

    for( i = 0; i < 12; ++i)
	r += RAN;

    return r;
}