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.gnu.org/licenses/gpl-2.0.html
19 *
20 * GPL HEADER END
21 */
22 /*
23 * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
24 * Use is subject to license terms.
25 */
26 /*
27 * This file is part of Lustre, http://www.lustre.org/
28 * Lustre is a trademark of Sun Microsystems, Inc.
29 *
30 * libcfs/libcfs/prng.c
31 *
32 * concatenation of following two 16-bit multiply with carry generators
33 * x(n)=a*x(n-1)+carry mod 2^16 and y(n)=b*y(n-1)+carry mod 2^16,
34 * number and carry packed within the same 32 bit integer.
35 * algorithm recommended by Marsaglia
36 */
37
38 #include "../../include/linux/libcfs/libcfs.h"
39
40 /*
41 * From: George Marsaglia <geo@stat.fsu.edu>
42 * Newsgroups: sci.math
43 * Subject: Re: A RANDOM NUMBER GENERATOR FOR C
44 * Date: Tue, 30 Sep 1997 05:29:35 -0700
45 *
46 * You may replace the two constants 36969 and 18000 by any
47 * pair of distinct constants from this list:
48 * 18000 18030 18273 18513 18879 19074 19098 19164 19215 19584
49 * 19599 19950 20088 20508 20544 20664 20814 20970 21153 21243
50 * 21423 21723 21954 22125 22188 22293 22860 22938 22965 22974
51 * 23109 23124 23163 23208 23508 23520 23553 23658 23865 24114
52 * 24219 24660 24699 24864 24948 25023 25308 25443 26004 26088
53 * 26154 26550 26679 26838 27183 27258 27753 27795 27810 27834
54 * 27960 28320 28380 28689 28710 28794 28854 28959 28980 29013
55 * 29379 29889 30135 30345 30459 30714 30903 30963 31059 31083
56 * (or any other 16-bit constants k for which both k*2^16-1
57 * and k*2^15-1 are prime)
58 */
59
60 #define RANDOM_CONST_A 18030
61 #define RANDOM_CONST_B 29013
62
63 static unsigned int seed_x = 521288629;
64 static unsigned int seed_y = 362436069;
65
66 /**
67 * cfs_rand - creates new seeds
68 *
69 * First it creates new seeds from the previous seeds. Then it generates a
70 * new pseudo random number for use.
71 *
72 * Returns a pseudo-random 32-bit integer
73 */
cfs_rand(void)74 unsigned int cfs_rand(void)
75 {
76 seed_x = RANDOM_CONST_A * (seed_x & 65535) + (seed_x >> 16);
77 seed_y = RANDOM_CONST_B * (seed_y & 65535) + (seed_y >> 16);
78
79 return ((seed_x << 16) + (seed_y & 65535));
80 }
81 EXPORT_SYMBOL(cfs_rand);
82
83 /**
84 * cfs_srand - sets the initial seed
85 * @seed1 : (seed_x) should have the most entropy in the low bits of the word
86 * @seed2 : (seed_y) should have the most entropy in the high bits of the word
87 *
88 * Replaces the original seeds with new values. Used to generate a new pseudo
89 * random numbers.
90 */
cfs_srand(unsigned int seed1,unsigned int seed2)91 void cfs_srand(unsigned int seed1, unsigned int seed2)
92 {
93 if (seed1)
94 seed_x = seed1; /* use default seeds if parameter is 0 */
95 if (seed2)
96 seed_y = seed2;
97 }
98 EXPORT_SYMBOL(cfs_srand);
99
100 /**
101 * cfs_get_random_bytes - generate a bunch of random numbers
102 * @buf : buffer to fill with random numbers
103 * @size: size of passed in buffer
104 *
105 * Fills a buffer with random bytes
106 */
cfs_get_random_bytes(void * buf,int size)107 void cfs_get_random_bytes(void *buf, int size)
108 {
109 int *p = buf;
110 int rem, tmp;
111
112 LASSERT(size >= 0);
113
114 rem = min((int)((unsigned long)buf & (sizeof(int) - 1)), size);
115 if (rem) {
116 get_random_bytes(&tmp, sizeof(tmp));
117 tmp ^= cfs_rand();
118 memcpy(buf, &tmp, rem);
119 p = buf + rem;
120 size -= rem;
121 }
122
123 while (size >= sizeof(int)) {
124 get_random_bytes(&tmp, sizeof(tmp));
125 *p = cfs_rand() ^ tmp;
126 size -= sizeof(int);
127 p++;
128 }
129 buf = p;
130 if (size) {
131 get_random_bytes(&tmp, sizeof(tmp));
132 tmp ^= cfs_rand();
133 memcpy(buf, &tmp, size);
134 }
135 }
136 EXPORT_SYMBOL(cfs_get_random_bytes);
137