From 4f57abfe66091281c9f59c14e6ea27b524b55d5b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Kristian=20H=C3=B8gsberg?= Date: Tue, 17 Nov 2009 11:14:54 -0500 Subject: Move libdrm/ up one level --- xf86drmRandom.c | 208 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 208 insertions(+) create mode 100644 xf86drmRandom.c (limited to 'xf86drmRandom.c') diff --git a/xf86drmRandom.c b/xf86drmRandom.c new file mode 100644 index 00000000..ecab9e2d --- /dev/null +++ b/xf86drmRandom.c @@ -0,0 +1,208 @@ +/* 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 + * + * 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 +#include + +#define RANDOM_MAIN 0 + +#if !RANDOM_MAIN +# include "xf86drm.h" +#endif + +#define RANDOM_MAGIC 0xfeedbeef +#define RANDOM_DEBUG 0 + +#if RANDOM_MAIN +#define RANDOM_ALLOC malloc +#define RANDOM_FREE free +#else +#define RANDOM_ALLOC drmMalloc +#define RANDOM_FREE drmFree +#endif + +typedef struct RandomState { + unsigned long magic; + unsigned long a; + unsigned long m; + unsigned long q; /* m div a */ + unsigned long r; /* m mod a */ + unsigned long check; + long seed; +} RandomState; + +#if RANDOM_MAIN +extern void *drmRandomCreate(unsigned long seed); +extern int drmRandomDestroy(void *state); +extern unsigned long drmRandom(void *state); +extern double drmRandomDouble(void *state); +#endif + +void *drmRandomCreate(unsigned long seed) +{ + RandomState *state; + + state = RANDOM_ALLOC(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; +} + +int drmRandomDestroy(void *state) +{ + RANDOM_FREE(state); + return 0; +} + +unsigned long drmRandom(void *state) +{ + RandomState *s = (RandomState *)state; + long hi; + long lo; + + hi = s->seed / s->q; + lo = s->seed % s->q; + s->seed = s->a * lo - s->r * hi; + if (s->seed <= 0) s->seed += s->m; + + return s->seed; +} + +double drmRandomDouble(void *state) +{ + RandomState *s = (RandomState *)state; + + return (double)drmRandom(state)/(double)s->m; +} + +#if RANDOM_MAIN +static void check_period(long seed) +{ + unsigned long count = 0; + unsigned long initial; + void *state; + + state = drmRandomCreate(seed); + initial = drmRandom(state); + ++count; + while (initial != drmRandom(state)) { + if (!++count) break; + } + printf("With seed of %10ld, period = %10lu (0x%08lx)\n", + seed, count, count); + drmRandomDestroy(state); +} + +int main(void) +{ + RandomState *state; + int i; + unsigned long rand; + + state = drmRandomCreate(1); + for (i = 0; i < 10000; i++) { + rand = drmRandom(state); + } + printf("After 10000 iterations: %lu (%lu expected): %s\n", + rand, state->check, + rand - state->check ? "*INCORRECT*" : "CORRECT"); + drmRandomDestroy(state); + + printf("Checking periods...\n"); + check_period(1); + check_period(2); + check_period(31415926); + + return 0; +} +#endif -- cgit v1.2.3