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/* 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, 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 */
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