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

   1 /* -*-c-*-
   2  *
   3  * Generic interface to random number generators
   4  *
   5  * (c) 1999 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Catacomb.
  11  *
  12  * Catacomb is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * Catacomb is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with Catacomb; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 /*----- Header files ------------------------------------------------------*/
  29
  30 #include <stddef.h>
  31
  32 #include <mLib/bits.h>
  33
  34 #include "grand.h"
  35
  36 /*----- Main code ---------------------------------------------------------*/
  37
  38 /* --- @grand_byte@ --- *
  39  *
  40  * Arguments:   @grand *r@ = pointet to generic generator
  41  *
  42  * Returns:     A uniformly-distributed pseudorandom integer in the interval
  43  *              %$[0, 256)$%.
  44  */
  45
  46 octet grand_byte(grand *r)
  47 {
  48   if (r->ops->byte != grand_byte)
  49     return (r->ops->byte(r));
  50   else if (r->ops->word != grand_word)
  51     return (r->ops->word(r) & 0xff);
  52   else if (r->ops->fill != grand_fill) {
  53     octet o;
  54     r->ops->fill(r, &o, 1);
  55     return (o);
  56   } else
  57     return (grand_range(r, 256));
  58 }
  59
  60 /* --- @grand_word@ --- *
  61  *
  62  * Arguments:   @grand *r@ = pointet to generic generator
  63  *
  64  * Returns:     A uniformly-distributed pseudorandom integer in the interval
  65  *              %$[0, 2^{32})$%.
  66  */
  67
  68 uint32 grand_word(grand *r)
  69 {
  70   if (r->ops->word != grand_word)
  71     return (r->ops->word(r));
  72   else {
  73     octet b[4];
  74     grand_fill(r, b, sizeof(b));
  75     return (LOAD32(b));
  76   }
  77 }
  78
  79 /* --- @grand_range@ --- *
  80  *
  81  * Arguments:   @grand *r@ = pointet to generic generator
  82  *              @uint32 l@ = limit for acceptable results
  83  *
  84  * Returns:     A uniformly-distributed pseudorandom integer in the interval
  85  *              %$[0, l)$%.
  86  */
  87
  88 uint32 grand_range(grand *r, uint32 l)
  89 {
  90   if (r->ops->range != grand_range)
  91     return (r->ops->range(r, l));
  92   else {
  93     uint32 m, z;
  94     uint32 (*w)(grand */*r*/);
  95     uint32 x;
  96
  97     /* --- Decide where to get data from --- *
  98      *
  99      * The choice of %$2^{32} - 1$% as a limit when using @grand_word@ isn't
 100      * wonderful, but working with %$2^{32}$% is awkward and the loss of a
 101      * few return values isn't significant.  The algorithm below still
 102      * successfully returns uniformly distributed results.
 103      */
 104
 105     if (r->ops->max) {
 106       w = r->ops->raw;
 107       m = r->ops->max;
 108     } else {
 109       w = grand_word;
 110       m = 0xffffffff;
 111     }
 112
 113     /* --- Work out maximum acceptable return value --- *
 114      *
 115      * This will be the highest multiple of @l@ less than @m@.
 116      */
 117
 118     z = m - (m % l);
 119
 120     /* --- Generate numbers until something acceptable is found --- *
 121      *
 122      * This will require an expected number of attempts less than 2.
 123      */
 124
 125     do x = w(r); while (x >= z);
 126     return (x % l);
 127   }
 128 }
 129
 130 /* --- @grand_fill@ --- *
 131  *
 132  * Arguments:   @grand *r@ = pointet to generic generator
 133  *              @void *p@ = pointer to a buffer
 134  *              @size_t sz@ = size of the buffer
 135  *
 136  * Returns:     ---
 137  *
 138  * Use:         Fills a buffer with uniformly distributed pseudorandom bytes
 139  *              (see @grand_byte@).
 140  */
 141
 142 void grand_fill(grand *r, void *p, size_t sz)
 143 {
 144   if (r->ops->fill != grand_fill)
 145     r->ops->fill(r, p, sz);
 146   else {
 147     octet *q = p;
 148     while (sz) {
 149       *q++ = r->ops->byte(r);
 150       sz--;
 151     }
 152   }
 153 }
 154
 155 /*----- That's all, folks -------------------------------------------------*/