/* random.c - Z-machine random number generator
 *	Copyright (c) 1995-1997 Stefan Jokisch
 *
 * This file is part of Frotz.
 *
 * Frotz 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; either version 2 of the License, or
 * (at your option) any later version.
 *
 * Frotz is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 */

#include "frotz.h"

static long A = 1;

static int interval = 0;
static int counter = 0;

/*
 * seed_random
 *
 * Set the seed value for the random number generator.
 *
 */

void seed_random (int value)
{

    if (value == 0) {		/* ask interface for seed value */
	A = os_random_seed ();
	interval = 0;
    } else if (value < 1000) {	/* special seed value */
	counter = 0;
	interval = value;
    } else {			/* standard seed value */
	A = value;
	interval = 0;
    }

}/* seed_random */

/*
 * z_random, store a random number or set the random number seed.
 *
 *	zargs[0] = range (positive) or seed value (negative)
 *
 */

void z_random ()
{

    if ((short) zargs[0] <= 0) {	/* set random seed */

	seed_random (- (short) zargs[0]);
	store (0);

    } else {				/* generate random number */

	zword result;

	if (interval != 0) {		/* ...in special mode */
	    result = counter++;
	    if (counter == interval) counter = 0;
	} else {			/* ...in standard mode */
	    A = 0x015a4e35L * A + 1;
	    result = (A >> 16) & 0x7fff;
	}

	store ((zword) (result % zargs[0] + 1));

    }

}/* z_random */
