apps/plugins/frotz/random.c

   1 /* random.c - Z-machine random number generator
   2  *      Copyright (c) 1995-1997 Stefan Jokisch
   3  *
   4  * This file is part of Frotz.
   5  *
   6  * Frotz is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * Frotz is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  19  */
  20
  21 #include "frotz.h"
  22
  23 static long A = 1;
  24
  25 static int interval = 0;
  26 static int counter = 0;
  27
  28 /*
  29  * seed_random
  30  *
  31  * Set the seed value for the random number generator.
  32  *
  33  */
  34
  35 void seed_random (int value)
  36 {
  37
  38     if (value == 0) {           /* ask interface for seed value */
  39         A = os_random_seed ();
  40         interval = 0;
  41     } else if (value < 1000) {  /* special seed value */
  42         counter = 0;
  43         interval = value;
  44     } else {                    /* standard seed value */
  45         A = value;
  46         interval = 0;
  47     }
  48
  49 }/* seed_random */
  50
  51 /*
  52  * z_random, store a random number or set the random number seed.
  53  *
  54  *      zargs[0] = range (positive) or seed value (negative)
  55  *
  56  */
  57
  58 void z_random ()
  59 {
  60
  61     if ((short) zargs[0] <= 0) {        /* set random seed */
  62
  63         seed_random (- (short) zargs[0]);
  64         store (0);
  65
  66     } else {                            /* generate random number */
  67
  68         zword result;
  69
  70         if (interval != 0) {            /* ...in special mode */
  71             result = counter++;
  72             if (counter == interval) counter = 0;
  73         } else {                        /* ...in standard mode */
  74             A = 0x015a4e35L * A + 1;
  75             result = (A >> 16) & 0x7fff;
  76         }
  77
  78         store ((zword) (result % zargs[0] + 1));
  79
  80     }
  81
  82 }/* z_random */