git.distorted.org.uk Git - u/mdw/catacomb/blob - grand.c

   1 /* -*-c-*-
   2  *
   3  * $Id: grand.c,v 1.3 2004/04/08 01:36:15 mdw Exp $
   4  *
   5  * Generic interface to random number generators
   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 /*----- Header files ------------------------------------------------------*/
  31
  32 #include <stddef.h>
  33
  34 #include <mLib/bits.h>
  35
  36 #include "grand.h"
  37
  38 /*----- Main code ---------------------------------------------------------*/
  39
  40 /* --- @grand_byte@ --- *
  41  *
  42  * Arguments:   @grand *r@ = pointet to generic generator
  43  *
  44  * Returns:     A uniformly-distributed pseudorandom integer in the interval
  45  *              %$[0, 256)$%.
  46  */
  47
  48 octet grand_byte(grand *r)
  49 {
  50   if (r->ops->byte != grand_byte)
  51     return (r->ops->byte(r));
  52   else if (r->ops->word != grand_word)
  53     return (r->ops->word(r) & 0xff);
  54   else if (r->ops->fill != grand_fill) {
  55     octet o;
  56     r->ops->fill(r, &o, 1);
  57     return (o);
  58   } else
  59     return (grand_range(r, 256));
  60 }
  61
  62 /* --- @grand_word@ --- *
  63  *
  64  * Arguments:   @grand *r@ = pointet to generic generator
  65  *
  66  * Returns:     A uniformly-distributed pseudorandom integer in the interval
  67  *              %$[0, 2^{32})$%.
  68  */
  69
  70 uint32 grand_word(grand *r)
  71 {
  72   if (r->ops->word != grand_word)
  73     return (r->ops->word(r));
  74   else {
  75     octet b[4];
  76     grand_fill(r, b, sizeof(b));
  77     return (LOAD32(b));
  78   }
  79 }
  80
  81 /* --- @grand_range@ --- *
  82  *
  83  * Arguments:   @grand *r@ = pointet to generic generator
  84  *              @uint32 l@ = limit for acceptable results
  85  *
  86  * Returns:     A uniformly-distributed pseudorandom integer in the interval
  87  *              %$[0, l)$%.
  88  */
  89
  90 uint32 grand_range(grand *r, uint32 l)
  91 {
  92   if (r->ops->range != grand_range)
  93     return (r->ops->range(r, l));
  94   else {
  95     uint32 m, z;
  96     uint32 (*w)(grand */*r*/);
  97     uint32 x;
  98
  99     /* --- Decide where to get data from --- *
 100      *
 101      * The choice of %$2^{32} - 1$% as a limit when using @grand_word@ isn't
 102      * wonderful, but working with %$2^{32}$% is awkward and the loss of a
 103      * few return values isn't significant.  The algorithm below still
 104      * successfully returns uniformly distributed results.
 105      */
 106
 107     if (r->ops->max) {
 108       w = r->ops->raw;
 109       m = r->ops->max;
 110     } else {
 111       w = grand_word;
 112       m = 0xffffffff;
 113     }
 114
 115     /* --- Work out maximum acceptable return value --- *
 116      *
 117      * This will be the highest multiple of @l@ less than @m@.
 118      */
 119
 120     z = m - (m % l);
 121
 122     /* --- Generate numbers until something acceptable is found --- *
 123      *
 124      * This will require an expected number of attempts less than 2.
 125      */
 126
 127     do x = w(r); while (x >= z);
 128     return (x % l);
 129   }
 130 }
 131
 132 /* --- @grand_fill@ --- *
 133  *
 134  * Arguments:   @grand *r@ = pointet to generic generator
 135  *              @void *p@ = pointer to a buffer
 136  *              @size_t sz@ = size of the buffer
 137  *
 138  * Returns:     ---
 139  *
 140  * Use:         Fills a buffer with uniformly distributed pseudorandom bytes
 141  *              (see @grand_byte@).
 142  */
 143
 144 void grand_fill(grand *r, void *p, size_t sz)
 145 {
 146   if (r->ops->fill != grand_fill)
 147     r->ops->fill(r, p, sz);
 148   else {
 149     octet *q = p;
 150     while (sz) {
 151       *q++ = r->ops->byte(r);
 152       sz--;
 153     }
 154   }
 155 }
 156
 157 /*----- That's all, folks -------------------------------------------------*/