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 #include "xf86drm.h"
78 #include "xf86drmRandom.h"
79
check_period(unsigned long seed)80 static void check_period(unsigned long seed)
81 {
82 unsigned long count = 0;
83 unsigned long initial;
84 void *state;
85
86 state = drmRandomCreate(seed);
87 initial = drmRandom(state);
88 ++count;
89 while (initial != drmRandom(state)) {
90 if (!++count) break;
91 }
92 printf("With seed of %10lu, period = %10lu (0x%08lx)\n",
93 seed, count, count);
94 drmRandomDestroy(state);
95 }
96
main(void)97 int main(void)
98 {
99 RandomState *state;
100 int i;
101 int ret;
102 unsigned long rand;
103
104 state = drmRandomCreate(1);
105 for (i = 0; i < 10000; i++) {
106 rand = drmRandom(state);
107 }
108 ret = rand != state->check;
109 printf("After 10000 iterations: %lu (%lu expected): %s\n",
110 rand, state->check,
111 ret ? "*INCORRECT*" : "CORRECT");
112 drmRandomDestroy(state);
113
114 printf("Checking periods...\n");
115 check_period(1);
116 check_period(2);
117 check_period(31415926);
118
119 return ret;
120 }
121