LXR linux/drivers/staging/lustre/lustre/libcfs/prng.c

   1/*
   2 * GPL HEADER START
   3 *
   4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   5 *
   6 * This program is free software; you can redistribute it and/or modify
   7 * it under the terms of the GNU General Public License version 2 only,
   8 * as published by the Free Software Foundation.
   9 *
  10 * This program is distributed in the hope that it will be useful, but
  11 * WITHOUT ANY WARRANTY; without even the implied warranty of
  12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 * General Public License version 2 for more details (a copy is included
  14 * in the LICENSE file that accompanied this code).
  15 *
  16 * You should have received a copy of the GNU General Public License
  17 * version 2 along with this program; If not, see
  18 * http://www.sun.com/software/products/lustre/docs/GPLv2.pdf
  19 *
  20 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  21 * CA 95054 USA or visit www.sun.com if you need additional information or
  22 * have any questions.
  23 *
  24 * GPL HEADER END
  25 */
  26/*
  27 * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
  28 * Use is subject to license terms.
  29 */
  30/*
  31 * This file is part of Lustre, http://www.lustre.org/
  32 * Lustre is a trademark of Sun Microsystems, Inc.
  33 *
  34 * libcfs/libcfs/prng.c
  35 *
  36 * concatenation of following two 16-bit multiply with carry generators
  37 * x(n)=a*x(n-1)+carry mod 2^16 and y(n)=b*y(n-1)+carry mod 2^16,
  38 * number and carry packed within the same 32 bit integer.
  39 * algorithm recommended by Marsaglia
  40*/
  41
  42#include <linux/libcfs/libcfs.h>
  43
  44/*
  45From: George Marsaglia <geo@stat.fsu.edu>
  46Newsgroups: sci.math
  47Subject: Re: A RANDOM NUMBER GENERATOR FOR C
  48Date: Tue, 30 Sep 1997 05:29:35 -0700
  49
  50 * You may replace the two constants 36969 and 18000 by any
  51 * pair of distinct constants from this list:
  52 * 18000 18030 18273 18513 18879 19074 19098 19164 19215 19584
  53 * 19599 19950 20088 20508 20544 20664 20814 20970 21153 21243
  54 * 21423 21723 21954 22125 22188 22293 22860 22938 22965 22974
  55 * 23109 23124 23163 23208 23508 23520 23553 23658 23865 24114
  56 * 24219 24660 24699 24864 24948 25023 25308 25443 26004 26088
  57 * 26154 26550 26679 26838 27183 27258 27753 27795 27810 27834
  58 * 27960 28320 28380 28689 28710 28794 28854 28959 28980 29013
  59 * 29379 29889 30135 30345 30459 30714 30903 30963 31059 31083
  60 * (or any other 16-bit constants k for which both k*2^16-1
  61 * and k*2^15-1 are prime) */
  62
  63#define RANDOM_CONST_A 18030
  64#define RANDOM_CONST_B 29013
  65
  66static unsigned int seed_x = 521288629;
  67static unsigned int seed_y = 362436069;
  68
  69/**
  70 * cfs_rand - creates new seeds
  71 *
  72 * First it creates new seeds from the previous seeds. Then it generates a
  73 * new psuedo random number for use.
  74 *
  75 * Returns a pseudo-random 32-bit integer
  76 */
  77unsigned int cfs_rand(void)
  78{
  79        seed_x = RANDOM_CONST_A * (seed_x & 65535) + (seed_x >> 16);
  80        seed_y = RANDOM_CONST_B * (seed_y & 65535) + (seed_y >> 16);
  81
  82        return ((seed_x << 16) + (seed_y & 65535));
  83}
  84EXPORT_SYMBOL(cfs_rand);
  85
  86/**
  87 * cfs_srand - sets the inital seed
  88 * @seed1 : (seed_x) should have the most entropy in the low bits of the word
  89 * @seed2 : (seed_y) should have the most entropy in the high bits of the word
  90 *
  91 * Replaces the original seeds with new values. Used to generate a new pseudo
  92 * random numbers.
  93 */
  94void cfs_srand(unsigned int seed1, unsigned int seed2)
  95{
  96        if (seed1)
  97                seed_x = seed1; /* use default seeds if parameter is 0 */
  98        if (seed2)
  99                seed_y = seed2;
 100}
 101EXPORT_SYMBOL(cfs_srand);
 102
 103/**
 104 * cfs_get_random_bytes - generate a bunch of random numbers
 105 * @buf : buffer to fill with random numbers
 106 * @size: size of passed in buffer
 107 *
 108 * Fills a buffer with random bytes
 109 */
 110void cfs_get_random_bytes(void *buf, int size)
 111{
 112        int *p = buf;
 113        int rem, tmp;
 114
 115        LASSERT(size >= 0);
 116
 117        rem = min((int)((unsigned long)buf & (sizeof(int) - 1)), size);
 118        if (rem) {
 119                get_random_bytes(&tmp, sizeof(tmp));
 120                tmp ^= cfs_rand();
 121                memcpy(buf, &tmp, rem);
 122                p = buf + rem;
 123                size -= rem;
 124        }
 125
 126        while (size >= sizeof(int)) {
 127                get_random_bytes(&tmp, sizeof(tmp));
 128                *p = cfs_rand() ^ tmp;
 129                size -= sizeof(int);
 130                p++;
 131        }
 132        buf = p;
 133        if (size) {
 134                get_random_bytes(&tmp, sizeof(tmp));
 135                tmp ^= cfs_rand();
 136                memcpy(buf, &tmp, size);
 137        }
 138}
 139EXPORT_SYMBOL(cfs_get_random_bytes);
 140