src/mesa/drivers/dri/dri_client/xf86drmRandom.c

   1 /* xf86drmRandom.c -- "Minimal Standard" PRNG Implementation
   2  * Created: Mon Apr 19 08:28:13 1999 by faith@precisioninsight.com
   3  *
   4  * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
   5  * All Rights Reserved.
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a
   8  * copy of this software and associated documentation files (the "Software"),
   9  * to deal in the Software without restriction, including without limitation
  10  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  11  * and/or sell copies of the Software, and to permit persons to whom the
  12  * Software is furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice (including the next
  15  * paragraph) shall be included in all copies or substantial portions of the
  16  * Software.
  17  *
  18  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  19  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  20  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  21  * PRECISION INSIGHT AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
  22  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  23  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  24  * DEALINGS IN THE SOFTWARE.
  25  *
  26  * Authors: Rickard E. (Rik) Faith <faith@valinux.com>
  27  *
  28  * $XFree86: xc/programs/Xserver/hw/xfree86/os-support/linux/drm/xf86drmRandom.c,v 1.4 2000/06/17 00:03:34 martin Exp $
  29  *
  30  * DESCRIPTION
  31  *
  32  * This file contains a simple, straightforward implementation of the Park
  33  * & Miller "Minimal Standard" PRNG [PM88, PMS93], which is a Lehmer
  34  * multiplicative linear congruential generator (MLCG) with a period of
  35  * 2^31-1.
  36  *
  37  * This implementation is intended to provide a reliable, portable PRNG
  38  * that is suitable for testing a hash table implementation and for
  39  * implementing skip lists.
  40  *
  41  * FUTURE ENHANCEMENTS
  42  *
  43  * If initial seeds are not selected randomly, two instances of the PRNG
  44  * can be correlated.  [Knuth81, pp. 32-33] describes a shuffling technique
  45  * that can eliminate this problem.
  46  *
  47  * If PRNGs are used for simulation, the period of the current
  48  * implementation may be too short.  [LE88] discusses methods of combining
  49  * MLCGs to produce much longer periods, and suggests some alternative
  50  * values for A and M.  [LE90 and Sch92] also provide information on
  51  * long-period PRNGs.
  52  *
  53  * REFERENCES
  54  *
  55  * [Knuth81] Donald E. Knuth. The Art of Computer Programming.  Volume 2:
  56  * Seminumerical Algorithms.  Reading, Massachusetts: Addison-Wesley, 1981.
  57  *
  58  * [LE88] Pierre L'Ecuyer. "Efficient and Portable Combined Random Number
  59  * Generators".  CACM 31(6), June 1988, pp. 742-774.
  60  *
  61  * [LE90] Pierre L'Ecuyer. "Random Numbers for Simulation". CACM 33(10,
  62  * October 1990, pp. 85-97.
  63  *
  64  * [PM88] Stephen K. Park and Keith W. Miller. "Random Number Generators:
  65  * Good Ones are Hard to Find". CACM 31(10), October 1988, pp. 1192-1201.
  66  *
  67  * [Sch92] Bruce Schneier. "Pseudo-Ransom Sequence Generator for 32-Bit
  68  * CPUs".  Dr. Dobb's Journal 17(2), February 1992, pp. 34, 37-38, 40.
  69  *
  70  * [PMS93] Stephen K. Park, Keith W. Miller, and Paul K. Stockmeyer.  In
  71  * "Technical Correspondence: Remarks on Choosing and Implementing Random
  72  * Number Generators". CACM 36(7), July 1993, pp. 105-110.
  73  *
  74  */
  75
  76 #define RANDOM_MAIN 0
  77
  78 #if RANDOM_MAIN
  79 # include <stdio.h>
  80 # include <stdlib.h>
  81 #else
  82 # include "xf86drm.h"
  83 # ifdef XFree86LOADER
  84 #  include "xf86.h"
  85 #  include "xf86_ansic.h"
  86 # else
  87 #  include <stdio.h>
  88 #  include <stdlib.h>
  89 # endif
  90 #endif
  91
  92 #define RANDOM_MAGIC 0xfeedbeef
  93 #define RANDOM_DEBUG 0
  94
  95 #if RANDOM_MAIN
  96 #define RANDOM_ALLOC malloc
  97 #define RANDOM_FREE  free
  98 #else
  99 #define RANDOM_ALLOC drmMalloc
 100 #define RANDOM_FREE  drmFree
 101 #endif
 102
 103 typedef struct RandomState {
 104     unsigned long magic;
 105     unsigned long a;
 106     unsigned long m;
 107     unsigned long q;            /* m div a */
 108     unsigned long r;            /* m mod a */
 109     unsigned long check;
 110     long          seed;
 111 } RandomState;
 112
 113 #if RANDOM_MAIN
 114 extern void          *drmRandomCreate(unsigned long seed);
 115 extern int           drmRandomDestroy(void *state);
 116 extern unsigned long drmRandom(void *state);
 117 extern double        drmRandomDouble(void *state);
 118 #endif
 119
 120 void *drmRandomCreate(unsigned long seed)
 121 {
 122     RandomState  *state;
 123
 124     state           = RANDOM_ALLOC(sizeof(*state));
 125     if (!state) return NULL;
 126     state->magic    = RANDOM_MAGIC;
 127 #if 0
 128                                 /* Park & Miller, October 1988 */
 129     state->a        = 16807;
 130     state->m        = 2147483647;
 131     state->check    = 1043618065; /* After 10000 iterations */
 132 #else
 133                                 /* Park, Miller, and Stockmeyer, July 1993 */
 134     state->a        = 48271;
 135     state->m        = 2147483647;
 136     state->check    = 399268537; /* After 10000 iterations */
 137 #endif
 138     state->q        = state->m / state->a;
 139     state->r        = state->m % state->a;
 140
 141     state->seed     = seed;
 142                                 /* Check for illegal boundary conditions,
 143                                    and choose closest legal value. */
 144     if (state->seed <= 0)        state->seed = 1;
 145     if (state->seed >= state->m) state->seed = state->m - 1;
 146
 147     return state;
 148 }
 149
 150 int drmRandomDestroy(void *state)
 151 {
 152     RANDOM_FREE(state);
 153     return 0;
 154 }
 155
 156 unsigned long drmRandom(void *state)
 157 {
 158     RandomState   *s = (RandomState *)state;
 159     long          hi;
 160     long          lo;
 161
 162     hi      = s->seed / s->q;
 163     lo      = s->seed % s->q;
 164     s->seed = s->a * lo - s->r * hi;
 165     if (s->seed <= 0) s->seed += s->m;
 166
 167     return s->seed;
 168 }
 169
 170 double drmRandomDouble(void *state)
 171 {
 172     RandomState *s = (RandomState *)state;
 173
 174     return (double)drmRandom(state)/(double)s->m;
 175 }
 176
 177 #if RANDOM_MAIN
 178 static void check_period(long seed)
 179 {
 180     unsigned long count = 0;
 181     unsigned long initial;
 182     void          *state;
 183
 184     state = drmRandomCreate(seed);
 185     initial = drmRandom(state);
 186     ++count;
 187     while (initial != drmRandom(state)) {
 188         if (!++count) break;
 189     }
 190     printf("With seed of %10ld, period = %10lu (0x%08lx)\n",
 191            seed, count, count);
 192     drmRandomDestroy(state);
 193 }
 194
 195 int main(void)
 196 {
 197     RandomState   *state;
 198     int           i;
 199     unsigned long rand;
 200
 201     state = drmRandomCreate(1);
 202     for (i = 0; i < 10000; i++) {
 203         rand = drmRandom(state);
 204     }
 205     printf("After 10000 iterations: %lu (%lu expected): %s\n",
 206            rand, state->check,
 207            rand - state->check ? "*INCORRECT*" : "CORRECT");
 208     drmRandomDestroy(state);
 209
 210     printf("Checking periods...\n");
 211     check_period(1);
 212     check_period(2);
 213     check_period(31415926);
 214
 215     return 0;
 216 }
 217 #endif