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   1 /* -*-c-*-
   2  *
   3  * $Id: lcrand.h,v 1.2 2000/06/17 11:28:51 mdw Exp $
   4  *
   5  * Simple linear congruential generator
   6  *
   7  * (c) 1999 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of Catacomb.
  13  *
  14  * Catacomb is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU Library General Public License as
  16  * published by the Free Software Foundation; either version 2 of the
  17  * License, or (at your option) any later version.
  18  *
  19  * Catacomb is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU Library General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU Library General Public
  25  * License along with Catacomb; if not, write to the Free
  26  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  27  * MA 02111-1307, USA.
  28  */
  29
  30 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: lcrand.h,v $
  33  * Revision 1.2  2000/06/17 11:28:51  mdw
  34  * Amend the notes slightly.
  35  *
  36  * Revision 1.1  1999/12/10 23:15:27  mdw
  37  * Noncryptographic random number generator.
  38  *
  39  */
  40
  41 /*----- Notes on the linear congruential generator ------------------------*
  42  *
  43  * This pseudorandom number generator is simple, but has absolutely no
  44  * cryptographic strength whatever.  It may be used whenever random numbers
  45  * are required but cryptographic strength is not, for example when
  46  * generating numbers for use in primality tests.  To be honest, it's not
  47  * even particularly fast, although a certain amount of effort has been
  48  * expended on making it better than awfully slow.  To put things in
  49  * perspective, it can't quite spit bytes out as fast as OFB DES.  (Then
  50  * again, bytes aren't its natural output format.)  Its main use is probably
  51  * seeding a Fibonacci generator.
  52  *
  53  * There exists a fixed-point input @LCRAND_FIXEDPT@ -- when fed to the
  54  * generator it comes straight back out again.  All other inputs less than
  55  * the modulus are part of the same sequence of period %$p - 1$%.
  56  *
  57  * The generator has been tested for its statistical properties.  George
  58  * Marsaglia's Diehard tests give it a reasonably clean bill of health.
  59  *
  60  * The modulus %$p$% is chosen as the largest prime number less than
  61  * %$2^{32}$%.  The multiplier %$a$% and additive constant %$c$% are based on
  62  * the decimal expansions of %$\pi$% and %$e$%, with the additional
  63  * restriction that the multiplier must be a primitive element modulo %$p$%.
  64  * The fixed point value is determined as %$c / (1 - a) \bmod p$%.
  65  */
  66
  67 #ifndef CATACOMB_LCRAND_H
  68 #define CATACOMB_LCRAND_H
  69
  70 #ifdef __cplusplus
  71   extern "C" {
  72 #endif
  73
  74 /*----- Header files ------------------------------------------------------*/
  75
  76 #include <mLib/bits.h>
  77
  78 #ifndef CATACOMB_GRAND_H
  79 #  include "grand.h"
  80 #endif
  81
  82 /*----- Constants ---------------------------------------------------------*/
  83
  84 #define LCRAND_P 4294967291u            /* Modulus for the generator */
  85 #define LCRAND_A 314159265u             /* Multiplier (primitive mod @p@) */
  86 #define LCRAND_C 271828183u             /* Additive constant */
  87
  88 #define LCRAND_FIXEDPT 3223959250u      /* Fixed point (only bad input) */
  89
  90 /*----- Functions provided ------------------------------------------------*/
  91
  92 /* --- @lcrand@ --- *
  93  *
  94  * Arguments:   @uint32 x@ = seed value
  95  *
  96  * Returns:     New state of the generator.
  97  *
  98  * Use:         Steps the generator.  Returns %$ax + c \bmod p$%.
  99  */
 100
 101 extern uint32 lcrand(uint32 /*x*/);
 102
 103 /* --- @lcrand_range@ --- *
 104  *
 105  * Arguments:   @uint32 *x@ = pointer to seed value (updated)
 106  *              @uint32 m@ = limit allowable
 107  *
 108  * Returns:     A uniformly distributed pseudorandom integer in the interval
 109  *              %$[0, m)$%.
 110  */
 111
 112 extern uint32 lcrand_range(uint32 */*x*/, uint32 /*m*/);
 113
 114 /* --- @lcrand_create@ --- *
 115  *
 116  * Arguments:   @uint32 x@ = initial seed
 117  *
 118  * Returns:     Pointer to a generic generator.
 119  *
 120  * Use:         Constructs a generic generator interface over a linear
 121  *              congruential generator.
 122  */
 123
 124 extern grand *lcrand_create(uint32 /*x*/);
 125
 126 /*----- That's all, folks -------------------------------------------------*/
 127
 128 #ifdef __cplusplus
 129   }
 130 #endif
 131
 132 #endif