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1/*
2 This is a maximally equidistributed combined Tausworthe generator
3 based on code from GNU Scientific Library 1.5 (30 Jun 2004)
4
5 x_n = (s1_n ^ s2_n ^ s3_n)
6
7 s1_{n+1} = (((s1_n & 4294967294) <<12) ^ (((s1_n <<13) ^ s1_n) >>19))
8 s2_{n+1} = (((s2_n & 4294967288) << 4) ^ (((s2_n << 2) ^ s2_n) >>25))
9 s3_{n+1} = (((s3_n & 4294967280) <<17) ^ (((s3_n << 3) ^ s3_n) >>11))
10
11 The period of this generator is about 2^88.
12
13 From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
14 Generators", Mathematics of Computation, 65, 213 (1996), 203--213.
15
16 This is available on the net from L'Ecuyer's home page,
17
18 http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
19 ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
20
21 There is an erratum in the paper "Tables of Maximally
22 Equidistributed Combined LFSR Generators", Mathematics of
23 Computation, 68, 225 (1999), 261--269:
24 http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
25
26 ... the k_j most significant bits of z_j must be non-
27 zero, for each j. (Note: this restriction also applies to the
28 computer code given in [4], but was mistakenly not mentioned in
29 that paper.)
30
31 This affects the seeding procedure by imposing the requirement
32 s1 > 1, s2 > 7, s3 > 15.
33
34*/
35
36#include <linux/types.h>
37#include <linux/percpu.h>
38#include <linux/module.h>
39#include <linux/random.h>
40
41struct rnd_state {
42 u32 s1, s2, s3;
43};
44
45static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
46
47static u32 __random32(struct rnd_state *state)
48{
49#define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b)
50
51 state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12);
52 state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4);
53 state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17);
54
55 return (state->s1 ^ state->s2 ^ state->s3);
56}
57
58static void __set_random32(struct rnd_state *state, unsigned long s)
59{
60 if (s == 0)
61 s = 1; /* default seed is 1 */
62
63#define LCG(n) (69069 * n)
64 state->s1 = LCG(s);
65 state->s2 = LCG(state->s1);
66 state->s3 = LCG(state->s2);
67
68 /* "warm it up" */
69 __random32(state);
70 __random32(state);
71 __random32(state);
72 __random32(state);
73 __random32(state);
74 __random32(state);
75}
76
77/**
78 * random32 - pseudo random number generator
79 *
80 * A 32 bit pseudo-random number is generated using a fast
81 * algorithm suitable for simulation. This algorithm is NOT
82 * considered safe for cryptographic use.
83 */
84u32 random32(void)
85{
86 unsigned long r;
87 struct rnd_state *state = &get_cpu_var(net_rand_state);
88 r = __random32(state);
89 put_cpu_var(state);
90 return r;
91}
92EXPORT_SYMBOL(random32);
93
94/**
95 * srandom32 - add entropy to pseudo random number generator
96 * @seed: seed value
97 *
98 * Add some additional seeding to the random32() pool.
99 * Note: this pool is per cpu so it only affects current CPU.
100 */
101void srandom32(u32 entropy)
102{
103 struct rnd_state *state = &get_cpu_var(net_rand_state);
104 __set_random32(state, state->s1 ^ entropy);
105 put_cpu_var(state);
106}
107EXPORT_SYMBOL(srandom32);
108
109/*
110 * Generate some initially weak seeding values to allow
111 * to start the random32() engine.
112 */
113static int __init random32_init(void)
114{
115 int i;
116
117 for_each_possible_cpu(i) {
118 struct rnd_state *state = &per_cpu(net_rand_state,i);
119 __set_random32(state, i + jiffies);
120 }
121 return 0;
122}
123core_initcall(random32_init);
124
125/*
126 * Generate better values after random number generator
127 * is fully initalized.
128 */
129static int __init random32_reseed(void)
130{
131 int i;
132 unsigned long seed;
133
134 for_each_possible_cpu(i) {
135 struct rnd_state *state = &per_cpu(net_rand_state,i);
136
137 get_random_bytes(&seed, sizeof(seed));
138 __set_random32(state, seed);
139 }
140 return 0;
141}
142late_initcall(random32_reseed);