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30 * libcfs/libcfs/prng.c
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
38 #include <linux/random.h>
39 #include <libcfs/libcfs.h>
42 From: George Marsaglia <geo@stat.fsu.edu>
44 Subject: Re: A RANDOM NUMBER GENERATOR FOR C
45 Date: Tue, 30 Sep 1997 05:29:35 -0700
47 * You may replace the two constants 36969 and 18000 by any
48 * pair of distinct constants from this list:
49 * 18000 18030 18273 18513 18879 19074 19098 19164 19215 19584
50 * 19599 19950 20088 20508 20544 20664 20814 20970 21153 21243
51 * 21423 21723 21954 22125 22188 22293 22860 22938 22965 22974
52 * 23109 23124 23163 23208 23508 23520 23553 23658 23865 24114
53 * 24219 24660 24699 24864 24948 25023 25308 25443 26004 26088
54 * 26154 26550 26679 26838 27183 27258 27753 27795 27810 27834
55 * 27960 28320 28380 28689 28710 28794 28854 28959 28980 29013
56 * 29379 29889 30135 30345 30459 30714 30903 30963 31059 31083
57 * (or any other 16-bit constants k for which both k*2^16-1
58 * and k*2^15-1 are prime) */
60 #define RANDOM_CONST_A 18030
61 #define RANDOM_CONST_B 29013
63 static unsigned int seed_x = 521288629;
64 static unsigned int seed_y = 362436069;
67 * cfs_rand - creates new seeds
69 * First it creates new seeds from the previous seeds. Then it generates a
70 * new psuedo random number for use.
72 * Returns a pseudo-random 32-bit integer
74 unsigned int cfs_rand(void)
76 seed_x = RANDOM_CONST_A * (seed_x & 65535) + (seed_x >> 16);
77 seed_y = RANDOM_CONST_B * (seed_y & 65535) + (seed_y >> 16);
79 return ((seed_x << 16) + (seed_y & 65535));
81 EXPORT_SYMBOL(cfs_rand);
84 * cfs_srand - sets the inital 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
88 * Replaces the original seeds with new values. Used to generate a new pseudo
91 void cfs_srand(unsigned int seed1, unsigned int seed2)
94 seed_x = seed1; /* use default seeds if parameter is 0 */
98 EXPORT_SYMBOL(cfs_srand);
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
105 * Fills a buffer with random bytes
107 void cfs_get_random_bytes(void *buf, int size)
114 rem = min((int)((unsigned long)buf & (sizeof(int) - 1)), size);
116 get_random_bytes(&tmp, sizeof(tmp));
118 memcpy(buf, &tmp, rem);
123 while (size >= sizeof(int)) {
124 get_random_bytes(&tmp, sizeof(tmp));
125 *p = cfs_rand() ^ tmp;
131 get_random_bytes(&tmp, sizeof(tmp));
133 memcpy(buf, &tmp, size);
136 EXPORT_SYMBOL(cfs_get_random_bytes);