rand.c

/*  Sarien - A Sierra AGI resource interpreter engine
 *  Copyright (C) 1999-2001 Stuart George and Claudio Matsuoka
 *  
 *  $Id: rand.c,v 1.9 2002/03/31 18:46:24 cmatsuoka Exp $
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; see docs/COPYING for further details.
 */

#ifndef PALMOS
#include <time.h>
#else
#define time(x) (x)
#endif

#include "sarien.h"
#include "rand.h"

#define RNG_M	2147483647L
#define RNG_A	48271L
#define RNG_Q	127773L
#define RNG_R	2836L


SINT32 rnd_seed;

static void set_xrnd_seed(SINT32 seedval)
{
	rnd_seed = (seedval % (RNG_M-1)) + 1;
}

static SINT32 xrnd(void)
{
	SINT32 low, high, test;

	high = rnd_seed / RNG_Q;
	low = rnd_seed % RNG_Q;
	test = RNG_A * low - RNG_R * high;

	return rnd_seed = test > 0 ? test : test + RNG_M;
}

/*
 * Public functions
 */

/**
 * Set the random number generator seed.
 */
void set_rnd_seed ()
{
	set_xrnd_seed(time(NULL));
}

/**
 * Read the random number generator seed.
 */
SINT32 get_rnd_seed ()
{
	return rnd_seed;
}

/**
 * Return random number.
 * This function returns a random value lesser than the specified value.
 */
SINT32 rnd (SINT32 maxrnd)
{
	return maxrnd ? xrnd() % maxrnd : xrnd();
}

/* end: rand.c */