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

   1 /* -*-c-*-
   2  *
   3  * $Id$
   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 AUTHORS 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.c,v $
  53  * Revision 1.2  2000/07/02 15:21:20  mdw
  54  * Fix licence text.
  55  *
  56  * Revision 1.1  2000/05/21 11:28:30  mdw
  57  * Initial check-in.
  58  *
  59  * --- Past lives (Catacomb) --- *
  60  *
  61  * Revision 1.1  1999/12/10 23:15:27  mdw
  62  * Noncryptographic random number generator.
  63  *
  64  */
  65
  66 /*----- Header files ------------------------------------------------------*/
  67
  68 #include <stdio.h>
  69 #include <stdlib.h>
  70 #include <string.h>
  71
  72 #include "bits.h"
  73 #include "fibrand.h"
  74 #include "lcrand.h"
  75
  76 /*----- Main code ---------------------------------------------------------*/
  77
  78 /* --- @fibrand_step@ --- *
  79  *
  80  * Arguments:   @fibrand *f@ = pointer to Fibonacci generator context
  81  *
  82  * Returns:     Next output from generator.
  83  *
  84  * Use:         Steps the generator.  Returns
  85  *              %$x_{i - 24} + x_{i - 55} \bmod 2^{32}$%.
  86  */
  87
  88 uint32 fibrand_step(fibrand *f)
  89 {
  90   unsigned i = f->i;
  91   unsigned j = i + (FIB_SZ - FIB_TAP);
  92   uint32 x;
  93   if (j >= FIB_SZ)
  94     j -= FIB_SZ;
  95   x = f->x[i] = U32(f->x[i] + f->x[j]);
  96   i++;
  97   if (i >= FIB_SZ)
  98     i = 0;
  99   f->i = i;
 100   return (x);
 101 }
 102
 103 /* --- @fibrand_lcseed@ --- *
 104  *
 105  * Arguments:   @fibrand *f@ = pointer to Fibonacci generator context
 106  *              @uint32 seed@ = seed value
 107  *
 108  * Returns:     ---
 109  *
 110  * Use:         Initializes a Fibonacci generator using outputs from the
 111  *              @lcrand@ generator seeded from @seed@.  This is faster than
 112  *              using a generic @lcrand@-based generator and @fibrand_rseed@
 113  *              because it uses raw outputs rather than uniformly distributed
 114  *              32-bit words.
 115  */
 116
 117 void fibrand_lcseed(fibrand *f, uint32 seed)
 118 {
 119   int i;
 120   unsigned p = 0;
 121
 122   for (i = 0; i < FIB_SZ; i++)
 123     p |= f->x[i] = seed = lcrand(seed);
 124   if (!(p & 1)) {
 125     i = lcrand_range(&seed, FIB_SZ);
 126     f->x[i] |= 1;
 127   }
 128   f->i = 0;
 129 }
 130
 131 /* --- @fibrand_range@ --- *
 132  *
 133  * Arguments:   @fibrand *f@ = pointer to Fibonacci generator context
 134  *              @uint32 m@ = limit
 135  *
 136  * Returns:     A uniformly distributed pseudorandom integer in the interval
 137  *              %$[0, m)$%.
 138  */
 139
 140 uint32 fibrand_range(fibrand *f, uint32 m)
 141 {
 142   uint32 r = 0xffffffff - (0xffffffff % m);
 143   uint x;
 144
 145   /* --- Now generate numbers until a good one comes along --- */
 146
 147   do x = fibrand_step(f); while (x >= r);
 148   return (x / (r / m));
 149 }
 150
 151 /*----- That's all, folks -------------------------------------------------*/