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authorKristian Høgsberg2009-11-17 10:14:54 -0600
committerKristian Høgsberg2009-11-17 10:15:06 -0600
commit4f57abfe66091281c9f59c14e6ea27b524b55d5b (patch)
treef00d1022cf208b381b93aa5c96858164e6a3f602 /xf86drmRandom.c
parent9dd3613073aa2491cef440725fdfa0cf1e8f1a42 (diff)
downloadexternal-libdrm-4f57abfe66091281c9f59c14e6ea27b524b55d5b.tar.gz
external-libdrm-4f57abfe66091281c9f59c14e6ea27b524b55d5b.tar.xz
external-libdrm-4f57abfe66091281c9f59c14e6ea27b524b55d5b.zip
Move libdrm/ up one level
Diffstat (limited to 'xf86drmRandom.c')
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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
94typedef 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
105extern void *drmRandomCreate(unsigned long seed);
106extern int drmRandomDestroy(void *state);
107extern unsigned long drmRandom(void *state);
108extern double drmRandomDouble(void *state);
109#endif
110
111void *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
141int drmRandomDestroy(void *state)
142{
143 RANDOM_FREE(state);
144 return 0;
145}
146
147unsigned 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
161double drmRandomDouble(void *state)
162{
163 RandomState *s = (RandomState *)state;
164
165 return (double)drmRandom(state)/(double)s->m;
166}
167
168#if RANDOM_MAIN
169static 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
186int 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