83 lines
1.9 KiB
C
83 lines
1.9 KiB
C
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/* random.c - Z-machine random number generator
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* Copyright (c) 1995-1997 Stefan Jokisch
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*
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* This file is part of Frotz.
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*
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* Frotz is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* Frotz is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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#include "frotz.h"
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static long A = 1;
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static int interval = 0;
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static int counter = 0;
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/*
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* seed_random
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*
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* Set the seed value for the random number generator.
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*
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*/
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void seed_random (int value)
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{
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if (value == 0) { /* ask interface for seed value */
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A = os_random_seed ();
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interval = 0;
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} else if (value < 1000) { /* special seed value */
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counter = 0;
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interval = value;
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} else { /* standard seed value */
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A = value;
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interval = 0;
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}
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}/* seed_random */
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/*
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* z_random, store a random number or set the random number seed.
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*
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* zargs[0] = range (positive) or seed value (negative)
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*
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*/
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void z_random ()
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{
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if ((short) zargs[0] <= 0) { /* set random seed */
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seed_random (- (short) zargs[0]);
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store (0);
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} else { /* generate random number */
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zword result;
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if (interval != 0) { /* ...in special mode */
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result = counter++;
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if (counter == interval) counter = 0;
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} else { /* ...in standard mode */
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A = 0x015a4e35L * A + 1;
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result = (A >> 16) & 0x7fff;
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}
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store ((zword) (result % zargs[0] + 1));
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}
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}/* z_random */
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