1
/* xf86drmRandom.c -- "Minimal Standard" PRNG Implementation
2
* Created: Mon Apr 19 08:28:13 1999 by faith@precisioninsight.com
4
* Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
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:
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
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.
26
* Authors: Rickard E. (Rik) Faith <faith@valinux.com>
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
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.
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.
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
53
* [Knuth81] Donald E. Knuth. The Art of Computer Programming. Volume 2:
54
* Seminumerical Algorithms. Reading, Massachusetts: Addison-Wesley, 1981.
56
* [LE88] Pierre L'Ecuyer. "Efficient and Portable Combined Random Number
57
* Generators". CACM 31(6), June 1988, pp. 742-774.
59
* [LE90] Pierre L'Ecuyer. "Random Numbers for Simulation". CACM 33(10,
60
* October 1990, pp. 85-97.
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.
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.
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.
83
#define RANDOM_MAGIC 0xfeedbeef
84
#define RANDOM_DEBUG 0
87
#define RANDOM_ALLOC malloc
88
#define RANDOM_FREE free
90
#define RANDOM_ALLOC drmMalloc
91
#define RANDOM_FREE drmFree
94
typedef struct RandomState {
98
unsigned long q; /* m div a */
99
unsigned long r; /* m mod a */
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);
111
void *drmRandomCreate(unsigned long seed)
115
state = RANDOM_ALLOC(sizeof(*state));
116
if (!state) return NULL;
117
state->magic = RANDOM_MAGIC;
119
/* Park & Miller, October 1988 */
121
state->m = 2147483647;
122
state->check = 1043618065; /* After 10000 iterations */
124
/* Park, Miller, and Stockmeyer, July 1993 */
126
state->m = 2147483647;
127
state->check = 399268537; /* After 10000 iterations */
129
state->q = state->m / state->a;
130
state->r = state->m % state->a;
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;
141
int drmRandomDestroy(void *state)
147
unsigned long drmRandom(void *state)
149
RandomState *s = (RandomState *)state;
155
s->seed = s->a * lo - s->r * hi;
156
if (s->seed <= 0) s->seed += s->m;
161
double drmRandomDouble(void *state)
163
RandomState *s = (RandomState *)state;
165
return (double)drmRandom(state)/(double)s->m;
169
static void check_period(long seed)
171
unsigned long count = 0;
172
unsigned long initial;
175
state = drmRandomCreate(seed);
176
initial = drmRandom(state);
178
while (initial != drmRandom(state)) {
181
printf("With seed of %10ld, period = %10lu (0x%08lx)\n",
183
drmRandomDestroy(state);
192
state = drmRandomCreate(1);
193
for (i = 0; i < 10000; i++) {
194
rand = drmRandom(state);
196
printf("After 10000 iterations: %lu (%lu expected): %s\n",
198
rand - state->check ? "*INCORRECT*" : "CORRECT");
199
drmRandomDestroy(state);
201
printf("Checking periods...\n");
204
check_period(31415926);
added
removed
xf86drmRandom.c
