1 /* -*- mode: c; c-basic-offset: 8; indent-tabs-mode: nil; -*-
2 * vim:expandtab:shiftwidth=8:tabstop=8:
4 * This file is part of the Lustre file system, http://www.lustre.org
5 * Lustre is a trademark of Cluster File Systems, Inc.
7 * concatenation of following two 16-bit multiply with carry generators
8 * x(n)=a*x(n-1)+carry mod 2^16 and y(n)=b*y(n-1)+carry mod 2^16,
9 * number and carry packed within the same 32 bit integer.
10 * algorithm recommended by Marsaglia
11 ******************************************************************/
13 # define EXPORT_SYMTAB
17 #include <liblustre.h>
19 #include <obd_class.h>
22 From: George Marsaglia <geo@stat.fsu.edu>
24 Subject: Re: A RANDOM NUMBER GENERATOR FOR C
25 Date: Tue, 30 Sep 1997 05:29:35 -0700
27 * You may replace the two constants 36969 and 18000 by any
28 * pair of distinct constants from this list:
29 * 18000 18030 18273 18513 18879 19074 19098 19164 19215 19584
30 * 19599 19950 20088 20508 20544 20664 20814 20970 21153 21243
31 * 21423 21723 21954 22125 22188 22293 22860 22938 22965 22974
32 * 23109 23124 23163 23208 23508 23520 23553 23658 23865 24114
33 * 24219 24660 24699 24864 24948 25023 25308 25443 26004 26088
34 * 26154 26550 26679 26838 27183 27258 27753 27795 27810 27834
35 * 27960 28320 28380 28689 28710 28794 28854 28959 28980 29013
36 * 29379 29889 30135 30345 30459 30714 30903 30963 31059 31083
37 * (or any other 16-bit constants k for which both k*2^16-1
38 * and k*2^15-1 are prime) */
40 #define RANDOM_CONST_A 18030
41 #define RANDOM_CONST_B 29013
43 static unsigned int seed_x = 521288629;
44 static unsigned int seed_y = 362436069;
45 unsigned int ll_rand(void)
48 seed_x = RANDOM_CONST_A * (seed_x & 65535) + (seed_x >> 16);
49 seed_y = RANDOM_CONST_B * (seed_y & 65535) + (seed_y >> 16);
51 return ((seed_x << 16) + (seed_y & 65535));
53 EXPORT_SYMBOL(ll_rand);
55 /* Note that if the input seeds are not completely random, then there is
56 * a preferred location for the entropy in the two seeds, in order to avoid
57 * the initial values from the PRNG to be the same each time.
59 * seed1 (seed_x) should have the most entropy in the low bits of the word
60 * seed2 (seed_y) should have the most entropy in the high bits of the word */
61 void ll_srand(unsigned int seed1, unsigned int seed2)
64 seed_x = seed1; /* use default seeds if parameter is 0 */
68 EXPORT_SYMBOL(ll_srand);