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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 | * 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 | |||
74 | #include <stdio.h> | ||
75 | #include <stdlib.h> | ||
76 | |||
77 | #define RANDOM_MAIN 0 | ||
78 | |||
79 | #if !RANDOM_MAIN | ||
80 | # include "xf86drm.h" | ||
81 | #endif | ||
82 | |||
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 | ||
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); | ||
109 | #endif | ||
110 | |||
111 | void *drmRandomCreate(unsigned long seed) | ||
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 | |||
141 | int drmRandomDestroy(void *state) | ||
142 | { | ||
143 | RANDOM_FREE(state); | ||
144 | return 0; | ||
145 | } | ||
146 | |||
147 | unsigned long drmRandom(void *state) | ||
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 | |||
161 | double drmRandomDouble(void *state) | ||
162 | { | ||
163 | RandomState *s = (RandomState *)state; | ||
164 | |||
165 | return (double)drmRandom(state)/(double)s->m; | ||
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 | |||
175 | state = drmRandomCreate(seed); | ||
176 | initial = drmRandom(state); | ||
177 | ++count; | ||
178 | while (initial != drmRandom(state)) { | ||
179 | if (!++count) break; | ||
180 | } | ||
181 | printf("With seed of %10ld, period = %10lu (0x%08lx)\n", | ||
182 | seed, count, count); | ||
183 | drmRandomDestroy(state); | ||
184 | } | ||
185 | |||
186 | int main(void) | ||
187 | { | ||
188 | RandomState *state; | ||
189 | int i; | ||
190 | unsigned long rand; | ||
191 | |||
192 | state = drmRandomCreate(1); | ||
193 | for (i = 0; i < 10000; i++) { | ||
194 | rand = drmRandom(state); | ||
195 | } | ||
196 | printf("After 10000 iterations: %lu (%lu expected): %s\n", | ||
197 | rand, state->check, | ||
198 | rand - state->check ? "*INCORRECT*" : "CORRECT"); | ||
199 | drmRandomDestroy(state); | ||
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 | ||