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aaa248f6 SH |
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 | ||
41 | struct rnd_state { | |
42 | u32 s1, s2, s3; | |
43 | }; | |
44 | ||
45 | static DEFINE_PER_CPU(struct rnd_state, net_rand_state); | |
46 | ||
47 | static 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 | ||
58 | static 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 | */ | |
84 | u32 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 | } | |
92 | EXPORT_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 | */ | |
101 | void 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 | } | |
107 | EXPORT_SYMBOL(srandom32); | |
108 | ||
109 | /* | |
110 | * Generate some initially weak seeding values to allow | |
111 | * to start the random32() engine. | |
112 | */ | |
113 | static 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 | } | |
123 | core_initcall(random32_init); | |
124 | ||
125 | /* | |
126 | * Generate better values after random number generator | |
127 | * is fully initalized. | |
128 | */ | |
129 | static 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 | } | |
142 | late_initcall(random32_reseed); |