1 /* xf86drmRandom.c -- "Minimal Standard" PRNG Implementation
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30  * This file contains a simple, straightforward implementation of the Park
32  * multiplicative linear congruential generator (MLCG) with a period of
33  * 2^31-1.
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
45  * If PRNGs are used for simulation, the period of the current
46  * implementation may be too short.  [LE88] discusses methods of combining
49  * long-period PRNGs.
53  * [Knuth81] Donald E. Knuth. The Art of Computer Programming.  Volume 2:
54  * Seminumerical Algorithms.  Reading, Massachusetts: Addison-Wesley, 1981.
57  * Generators".  CACM 31(6), June 1988, pp. 742-774.
60  * October 1990, pp. 85-97.
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.
70  * Number Generators". CACM 36(7), July 1993, pp. 105-110.
85     RandomState  *state;  in drmRandomCreate()  local
87     state           = drmMalloc(sizeof(*state));  in drmRandomCreate()
88     if (!state) return NULL;  in drmRandomCreate()
89     state->magic    = RANDOM_MAGIC;  in drmRandomCreate()
92     state->a        = 16807;  in drmRandomCreate()
93     state->m        = 2147483647;  in drmRandomCreate()
94     state->check    = 1043618065; /* After 10000 iterations */  in drmRandomCreate()
97     state->a        = 48271;  in drmRandomCreate()
98     state->m        = 2147483647;  in drmRandomCreate()
99     state->check    = 399268537; /* After 10000 iterations */  in drmRandomCreate()
101     state->q        = state->m / state->a;  in drmRandomCreate()
102     state->r        = state->m % state->a;  in drmRandomCreate()
104     state->seed     = seed;  in drmRandomCreate()
107     if (state->seed <= 0)        state->seed = 1;  in drmRandomCreate()
108     if (state->seed >= state->m) state->seed = state->m - 1;  in drmRandomCreate()
110     return state;  in drmRandomCreate()
113 drm_public int drmRandomDestroy(void *state)  in drmRandomDestroy()  argument
115     drmFree(state);  in drmRandomDestroy()
119 drm_public unsigned long drmRandom(void *state)  in drmRandom()  argument
121     RandomState   *s = (RandomState *)state;  in drmRandom()
125     hi      = s->seed / s->q;  in drmRandom()
126     lo      = s->seed % s->q;  in drmRandom()
127     s->seed = s->a * lo - s->r * hi;  in drmRandom()
128     if ((s->a * lo) <= (s->r * hi)) s->seed += s->m;  in drmRandom()
130     return s->seed;  in drmRandom()
133 drm_public double drmRandomDouble(void *state)  in drmRandomDouble()  argument
135     RandomState *s = (RandomState *)state;  in drmRandomDouble()
137     return (double)drmRandom(state)/(double)s->m;  in drmRandomDouble()