mdw@git.distorted.org.uk Git - newkind/blob - random.c

   1 /*
   2  * Elite - The New Kind.
   3  *
   4  * Reverse engineered from the BBC disk version of Elite.
   5  * Additional material by C.J.Pinder.
   6  *
   7  * The original Elite code is (C) I.Bell & D.Braben 1984.
   8  * This version re-engineered in C by C.J.Pinder 1999-2001.
   9  *
  10  * email: <christian@newkind.co.uk>
  11  *
  12  *
  13  */
  14
  15 /*
  16  * random.c
  17  */
  18
  19
  20 #include <stdlib.h>
  21 #include "allegro.h"
  22
  23 #include "random.h"
  24
  25 static int rand_seed;
  26
  27 /*
  28  * Portable random number generator implementing the recursion:
  29  *     IX = 16807 * IX MOD (2**(31) - 1)
  30  * Using only 32 bits, including sign.
  31  *
  32  * Taken from "A Guide to Simulation" by Bratley, Fox and Schrage.
  33  */
  34
  35 int randint (void)
  36 {
  37         int k1;
  38         int ix = rand_seed;
  39
  40         k1 = ix / 127773;
  41         ix = 16807 * (ix - k1 * 127773) - k1 * 2836;
  42         if (ix < 0)
  43                 ix += 2147483647;
  44         rand_seed = ix;
  45
  46         return ix;
  47 }
  48
  49
  50 void set_rand_seed (int seed)
  51 {
  52         rand_seed = seed;
  53 }
  54
  55
  56 int get_rand_seed (void)
  57 {
  58         return rand_seed;
  59 }
  60
  61 int rand255 (void)
  62 {
  63         return (randint() & 255);
  64 }