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- /* xf86drmRandom.c -- "Minimal Standard" PRNG Implementation
- * Created: Mon Apr 19 08:28:13 1999 by faith@precisioninsight.com
- *
- * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
- * All Rights Reserved.
- *
- * Permission is hereby granted, free of charge, to any person obtaining a
- * copy of this software and associated documentation files (the "Software"),
- * to deal in the Software without restriction, including without limitation
- * the rights to use, copy, modify, merge, publish, distribute, sublicense,
- * and/or sell copies of the Software, and to permit persons to whom the
- * Software is furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice (including the next
- * paragraph) shall be included in all copies or substantial portions of the
- * Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
- * PRECISION INSIGHT AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
- * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
- * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
- * DEALINGS IN THE SOFTWARE.
- *
- * Authors: Rickard E. (Rik) Faith <faith@valinux.com>
- *
- * DESCRIPTION
- *
- * This file contains a simple, straightforward implementation of the Park
- * & Miller "Minimal Standard" PRNG [PM88, PMS93], which is a Lehmer
- * multiplicative linear congruential generator (MLCG) with a period of
- * 2^31-1.
- *
- * This implementation is intended to provide a reliable, portable PRNG
- * that is suitable for testing a hash table implementation and for
- * implementing skip lists.
- *
- * FUTURE ENHANCEMENTS
- *
- * If initial seeds are not selected randomly, two instances of the PRNG
- * can be correlated. [Knuth81, pp. 32-33] describes a shuffling technique
- * that can eliminate this problem.
- *
- * If PRNGs are used for simulation, the period of the current
- * implementation may be too short. [LE88] discusses methods of combining
- * MLCGs to produce much longer periods, and suggests some alternative
- * values for A and M. [LE90 and Sch92] also provide information on
- * long-period PRNGs.
- *
- * REFERENCES
- *
- * [Knuth81] Donald E. Knuth. The Art of Computer Programming. Volume 2:
- * Seminumerical Algorithms. Reading, Massachusetts: Addison-Wesley, 1981.
- *
- * [LE88] Pierre L'Ecuyer. "Efficient and Portable Combined Random Number
- * Generators". CACM 31(6), June 1988, pp. 742-774.
- *
- * [LE90] Pierre L'Ecuyer. "Random Numbers for Simulation". CACM 33(10,
- * October 1990, pp. 85-97.
- *
- * [PM88] Stephen K. Park and Keith W. Miller. "Random Number Generators:
- * Good Ones are Hard to Find". CACM 31(10), October 1988, pp. 1192-1201.
- *
- * [Sch92] Bruce Schneier. "Pseudo-Ransom Sequence Generator for 32-Bit
- * CPUs". Dr. Dobb's Journal 17(2), February 1992, pp. 34, 37-38, 40.
- *
- * [PMS93] Stephen K. Park, Keith W. Miller, and Paul K. Stockmeyer. In
- * "Technical Correspondence: Remarks on Choosing and Implementing Random
- * Number Generators". CACM 36(7), July 1993, pp. 105-110.
- *
- */
- #include <stdio.h>
- #include <stdlib.h>
- #include "libdrm_macros.h"
- #include "xf86drm.h"
- #include "xf86drmRandom.h"
- #define RANDOM_MAGIC 0xfeedbeef
- drm_public void *drmRandomCreate(unsigned long seed)
- {
- RandomState *state;
- state = drmMalloc(sizeof(*state));
- if (!state) return NULL;
- state->magic = RANDOM_MAGIC;
- #if 0
- /* Park & Miller, October 1988 */
- state->a = 16807;
- state->m = 2147483647;
- state->check = 1043618065; /* After 10000 iterations */
- #else
- /* Park, Miller, and Stockmeyer, July 1993 */
- state->a = 48271;
- state->m = 2147483647;
- state->check = 399268537; /* After 10000 iterations */
- #endif
- state->q = state->m / state->a;
- state->r = state->m % state->a;
- state->seed = seed;
- /* Check for illegal boundary conditions,
- and choose closest legal value. */
- if (state->seed <= 0) state->seed = 1;
- if (state->seed >= state->m) state->seed = state->m - 1;
- return state;
- }
- drm_public int drmRandomDestroy(void *state)
- {
- drmFree(state);
- return 0;
- }
- drm_public unsigned long drmRandom(void *state)
- {
- RandomState *s = (RandomState *)state;
- unsigned long hi;
- unsigned long lo;
- hi = s->seed / s->q;
- lo = s->seed % s->q;
- s->seed = s->a * lo - s->r * hi;
- if ((s->a * lo) <= (s->r * hi)) s->seed += s->m;
- return s->seed;
- }
- drm_public double drmRandomDouble(void *state)
- {
- RandomState *s = (RandomState *)state;
-
- return (double)drmRandom(state)/(double)s->m;
- }
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