mdw@git.distorted.org.uk Git - storin/blob - fibrand.h

   1 /* -*-c-*-
   2  *
   3  * $Id: fibrand.h,v 1.1 2000/05/21 11:28:30 mdw Exp $
   4  *
   5  * Fibonacci generator
   6  *
   7  * (c) 1999 Straylight/Edgeware
   8  * (c) 2000 Mark Wooding
   9  */
  10
  11 /*----- Licensing notice --------------------------------------------------*
  12  *
  13  * Copyright (c) 2000 Mark Wooding
  14  * All rights reserved.
  15  *
  16  * Redistribution and use in source and binary forms, with or without
  17  * modification, are permitted provided that the following conditions are
  18  * met:
  19  *
  20  * 1. Redistributions of source code must retain the above copyright
  21  *    notice, this list of conditions and the following disclaimer.
  22  *
  23  * 2, Redistributions in binary form must reproduce the above copyright
  24  *    notice, this list of conditions and the following disclaimer in the
  25  *    documentation and/or other materials provided with the distribution.
  26  *
  27  * 3. The name of the authors may not be used to endorse or promote
  28  *    products derived from this software without specific prior written
  29  *    permission.
  30  *
  31  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
  32  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  33  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN
  34  * NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
  35  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  36  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  37  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  38  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  39  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  40  * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  41  * POSSIBILITY OF SUCH DAMAGE.
  42  *
  43  * Instead of accepting the above terms, you may redistribute and/or modify
  44  * this software under the terms of either the GNU General Public License,
  45  * or the GNU Library General Public License, published by the Free
  46  * Software Foundation; either version 2 of the License, or (at your
  47  * option) any later version.
  48  */
  49
  50 /*----- Revision history --------------------------------------------------*
  51  *
  52  * $Log: fibrand.h,v $
  53  * Revision 1.1  2000/05/21 11:28:30  mdw
  54  * Initial check-in.
  55  *
  56  * --- Past lives (Catacomb) --- *
  57  *
  58  * Revision 1.1  1999/12/10 23:15:27  mdw
  59  * Noncryptographic random number generator.
  60  *
  61  */
  62
  63 /*----- Notes on the Fibonacci generator ----------------------------------*
  64  *
  65  * The generator was originally suggested by G. J. Mitchell and D. P. Moore
  66  * in 1957, and publicized by D. E. Knuth as Algorithm 3.2.2A in volume 2 of
  67  * his work `The Art of Computer Programming'.  The generator is simple: at
  68  * each stage it emits %$x_n = (x_{n - 55} + x_{n - 24}) \bmod 2^{32}$%.  The
  69  * period is proven to be greater than %$2^{55}$%, and statistical properties
  70  * appear to be good.
  71  */
  72
  73 #ifndef FIBRAND_H
  74 #define FIBRAND_H
  75
  76 #ifdef __cplusplus
  77   extern "C" {
  78 #endif
  79
  80 /*----- Header files ------------------------------------------------------*/
  81
  82 #ifndef BITS_H
  83 #  include "bits.h"
  84 #endif
  85
  86 /*----- Magic constants ---------------------------------------------------*/
  87
  88 #define FIB_SZ 55
  89 #define FIB_TAP 24
  90
  91 /*----- Data structures ---------------------------------------------------*/
  92
  93 typedef struct fibrand {
  94   unsigned i;
  95   uint32 x[FIB_SZ];
  96 } fibrand;
  97
  98 /*----- Functions provided ------------------------------------------------*/
  99
 100 /* --- @fibrand_step@ --- *
 101  *
 102  * Arguments:   @fibrand *f@ = pointer to Fibonacci generator context
 103  *
 104  * Returns:     Next output from generator.
 105  *
 106  * Use:         Steps the generator.  Returns
 107  *              %$x_{i - 24} + x_{i - 55} \bmod 2^{32}$%.
 108  */
 109
 110 extern uint32 fibrand_step(fibrand */*f*/);
 111
 112 /* --- @fibrand_lcseed@ --- *
 113  *
 114  * Arguments:   @fibrand *f@ = pointer to Fibonacci generator context
 115  *              @uint32 seed@ = seed value
 116  *
 117  * Returns:     ---
 118  *
 119  * Use:         Initializes a Fibonacci generator using outputs from the
 120  *              @lcrand@ generator seeded from @seed@.  This is faster than
 121  *              using a generic @lcrand@-based generator and @fibrand_rseed@
 122  *              because it uses raw outputs rather than uniformly distributed
 123  *              32-bit words.
 124  */
 125
 126 extern void fibrand_lcseed(fibrand */*f*/, uint32 /*seed*/);
 127
 128 /* --- @fibrand_range@ --- *
 129  *
 130  * Arguments:   @fibrand *f@ = pointer to Fibonacci generator context
 131  *              @uint32 m@ = limit
 132  *
 133  * Returns:     A uniformly distributed pseudorandom integer in the interval
 134  *              %$[0, m)$%.
 135  */
 136
 137 extern uint32 fibrand_range(fibrand */*f*/, uint32 /*m*/);
 138
 139 /*----- That's all, folks -------------------------------------------------*/
 140
 141 #ifdef __cplusplus
 142   }
 143 #endif
 144
 145 #endif