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 #include "xf86drm.h" 78 #include "xf86drmRandom.h" 79 80 static void check_period(unsigned long seed) 81 { 82 unsigned long count = 0; 83 unsigned long initial; 84 void *state; 85 86 state = drmRandomCreate(seed); 87 initial = drmRandom(state); 88 ++count; 89 while (initial != drmRandom(state)) { 90 if (!++count) break; 91 } 92 printf("With seed of %10lu, period = %10lu (0x%08lx)\n", 93 seed, count, count); 94 drmRandomDestroy(state); 95 } 96 97 int main(void) 98 { 99 RandomState *state; 100 int i; 101 int ret; 102 unsigned long rand; 103 104 state = drmRandomCreate(1); 105 for (i = 0; i < 10000; i++) { 106 rand = drmRandom(state); 107 } 108 ret = rand != state->check; 109 printf("After 10000 iterations: %lu (%lu expected): %s\n", 110 rand, state->check, 111 ret ? "*INCORRECT*" : "CORRECT"); 112 drmRandomDestroy(state); 113 114 printf("Checking periods...\n"); 115 check_period(1); 116 check_period(2); 117 check_period(31415926); 118 119 return ret; 120 } 121