Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 1 | /* xf86drmRandom.c -- "Minimal Standard" PRNG Implementation |
| 2 | * Created: Mon Apr 19 08:28:13 1999 by faith@precisioninsight.com |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 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 | * |
Rik Faith | 1c8b2b5 | 2000-06-13 14:22:03 +0000 | [diff] [blame] | 26 | * Authors: Rickard E. (Rik) Faith <faith@valinux.com> |
| 27 | * |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 28 | * DESCRIPTION |
| 29 | * |
| 30 | * This file contains a simple, straightforward implementation of the Park |
| 31 | * & Miller "Minimal Standard" PRNG [PM88, PMS93], which is a Lehmer |
| 32 | * multiplicative linear congruential generator (MLCG) with a period of |
| 33 | * 2^31-1. |
| 34 | * |
| 35 | * This implementation is intended to provide a reliable, portable PRNG |
| 36 | * that is suitable for testing a hash table implementation and for |
| 37 | * implementing skip lists. |
| 38 | * |
| 39 | * FUTURE ENHANCEMENTS |
| 40 | * |
| 41 | * If initial seeds are not selected randomly, two instances of the PRNG |
| 42 | * can be correlated. [Knuth81, pp. 32-33] describes a shuffling technique |
| 43 | * that can eliminate this problem. |
| 44 | * |
| 45 | * If PRNGs are used for simulation, the period of the current |
| 46 | * implementation may be too short. [LE88] discusses methods of combining |
| 47 | * MLCGs to produce much longer periods, and suggests some alternative |
| 48 | * values for A and M. [LE90 and Sch92] also provide information on |
| 49 | * long-period PRNGs. |
| 50 | * |
| 51 | * REFERENCES |
| 52 | * |
| 53 | * [Knuth81] Donald E. Knuth. The Art of Computer Programming. Volume 2: |
| 54 | * Seminumerical Algorithms. Reading, Massachusetts: Addison-Wesley, 1981. |
| 55 | * |
| 56 | * [LE88] Pierre L'Ecuyer. "Efficient and Portable Combined Random Number |
| 57 | * Generators". CACM 31(6), June 1988, pp. 742-774. |
| 58 | * |
| 59 | * [LE90] Pierre L'Ecuyer. "Random Numbers for Simulation". CACM 33(10, |
| 60 | * October 1990, pp. 85-97. |
| 61 | * |
| 62 | * [PM88] Stephen K. Park and Keith W. Miller. "Random Number Generators: |
| 63 | * Good Ones are Hard to Find". CACM 31(10), October 1988, pp. 1192-1201. |
| 64 | * |
| 65 | * [Sch92] Bruce Schneier. "Pseudo-Ransom Sequence Generator for 32-Bit |
| 66 | * CPUs". Dr. Dobb's Journal 17(2), February 1992, pp. 34, 37-38, 40. |
| 67 | * |
| 68 | * [PMS93] Stephen K. Park, Keith W. Miller, and Paul K. Stockmeyer. In |
| 69 | * "Technical Correspondence: Remarks on Choosing and Implementing Random |
| 70 | * Number Generators". CACM 36(7), July 1993, pp. 105-110. |
| 71 | * |
| 72 | */ |
| 73 | |
George Sapountzis | b69b426 | 2007-04-26 14:15:55 +0300 | [diff] [blame] | 74 | #include <stdio.h> |
| 75 | #include <stdlib.h> |
Adam Jackson | f28dddb | 2005-11-30 03:51:46 +0000 | [diff] [blame] | 76 | |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 77 | #define RANDOM_MAIN 0 |
| 78 | |
George Sapountzis | b69b426 | 2007-04-26 14:15:55 +0300 | [diff] [blame] | 79 | #if !RANDOM_MAIN |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 80 | # include "xf86drm.h" |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 81 | #endif |
| 82 | |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 83 | #define RANDOM_MAGIC 0xfeedbeef |
| 84 | #define RANDOM_DEBUG 0 |
| 85 | |
| 86 | #if RANDOM_MAIN |
| 87 | #define RANDOM_ALLOC malloc |
| 88 | #define RANDOM_FREE free |
| 89 | #else |
| 90 | #define RANDOM_ALLOC drmMalloc |
| 91 | #define RANDOM_FREE drmFree |
| 92 | #endif |
| 93 | |
| 94 | typedef struct RandomState { |
| 95 | unsigned long magic; |
| 96 | unsigned long a; |
| 97 | unsigned long m; |
| 98 | unsigned long q; /* m div a */ |
| 99 | unsigned long r; /* m mod a */ |
| 100 | unsigned long check; |
| 101 | long seed; |
| 102 | } RandomState; |
| 103 | |
| 104 | #if RANDOM_MAIN |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 105 | extern void *drmRandomCreate(unsigned long seed); |
| 106 | extern int drmRandomDestroy(void *state); |
| 107 | extern unsigned long drmRandom(void *state); |
| 108 | extern double drmRandomDouble(void *state); |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 109 | #endif |
| 110 | |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 111 | void *drmRandomCreate(unsigned long seed) |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 112 | { |
| 113 | RandomState *state; |
| 114 | |
| 115 | state = RANDOM_ALLOC(sizeof(*state)); |
| 116 | if (!state) return NULL; |
| 117 | state->magic = RANDOM_MAGIC; |
| 118 | #if 0 |
| 119 | /* Park & Miller, October 1988 */ |
| 120 | state->a = 16807; |
| 121 | state->m = 2147483647; |
| 122 | state->check = 1043618065; /* After 10000 iterations */ |
| 123 | #else |
| 124 | /* Park, Miller, and Stockmeyer, July 1993 */ |
| 125 | state->a = 48271; |
| 126 | state->m = 2147483647; |
| 127 | state->check = 399268537; /* After 10000 iterations */ |
| 128 | #endif |
| 129 | state->q = state->m / state->a; |
| 130 | state->r = state->m % state->a; |
| 131 | |
| 132 | state->seed = seed; |
| 133 | /* Check for illegal boundary conditions, |
| 134 | and choose closest legal value. */ |
| 135 | if (state->seed <= 0) state->seed = 1; |
| 136 | if (state->seed >= state->m) state->seed = state->m - 1; |
| 137 | |
| 138 | return state; |
| 139 | } |
| 140 | |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 141 | int drmRandomDestroy(void *state) |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 142 | { |
| 143 | RANDOM_FREE(state); |
| 144 | return 0; |
| 145 | } |
| 146 | |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 147 | unsigned long drmRandom(void *state) |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 148 | { |
| 149 | RandomState *s = (RandomState *)state; |
| 150 | long hi; |
| 151 | long lo; |
| 152 | |
| 153 | hi = s->seed / s->q; |
| 154 | lo = s->seed % s->q; |
| 155 | s->seed = s->a * lo - s->r * hi; |
| 156 | if (s->seed <= 0) s->seed += s->m; |
| 157 | |
| 158 | return s->seed; |
| 159 | } |
| 160 | |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 161 | double drmRandomDouble(void *state) |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 162 | { |
| 163 | RandomState *s = (RandomState *)state; |
| 164 | |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 165 | return (double)drmRandom(state)/(double)s->m; |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 166 | } |
| 167 | |
| 168 | #if RANDOM_MAIN |
| 169 | static void check_period(long seed) |
| 170 | { |
| 171 | unsigned long count = 0; |
| 172 | unsigned long initial; |
| 173 | void *state; |
| 174 | |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 175 | state = drmRandomCreate(seed); |
| 176 | initial = drmRandom(state); |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 177 | ++count; |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 178 | while (initial != drmRandom(state)) { |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 179 | if (!++count) break; |
| 180 | } |
| 181 | printf("With seed of %10ld, period = %10lu (0x%08lx)\n", |
| 182 | seed, count, count); |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 183 | drmRandomDestroy(state); |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 184 | } |
| 185 | |
| 186 | int main(void) |
| 187 | { |
| 188 | RandomState *state; |
| 189 | int i; |
| 190 | unsigned long rand; |
| 191 | |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 192 | state = drmRandomCreate(1); |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 193 | for (i = 0; i < 10000; i++) { |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 194 | rand = drmRandom(state); |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 195 | } |
| 196 | printf("After 10000 iterations: %lu (%lu expected): %s\n", |
| 197 | rand, state->check, |
| 198 | rand - state->check ? "*INCORRECT*" : "CORRECT"); |
Adam Jackson | 22e41ef | 2006-02-20 23:09:00 +0000 | [diff] [blame] | 199 | drmRandomDestroy(state); |
Daryll Strauss | b3a5766 | 1999-12-05 01:19:48 +0000 | [diff] [blame] | 200 | |
| 201 | printf("Checking periods...\n"); |
| 202 | check_period(1); |
| 203 | check_period(2); |
| 204 | check_period(31415926); |
| 205 | |
| 206 | return 0; |
| 207 | } |
| 208 | #endif |