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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/jiffies.h> |
40 | #include <linux/random.h> |
41 | |
42 | static DEFINE_PER_CPU(struct rnd_state, net_rand_state); |
43 | |
44 | /** |
45 | * prandom32 - seeded pseudo-random number generator. |
46 | * @state: pointer to state structure holding seeded state. |
47 | * |
48 | * This is used for pseudo-randomness with no outside seeding. |
49 | * For more random results, use random32(). |
50 | */ |
51 | u32 prandom32(struct rnd_state *state) |
52 | { |
53 | #define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b) |
54 | |
55 | state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12); |
56 | state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4); |
57 | state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17); |
58 | |
59 | return (state->s1 ^ state->s2 ^ state->s3); |
60 | } |
61 | EXPORT_SYMBOL(prandom32); |
62 | |
63 | /** |
64 | * random32 - pseudo random number generator |
65 | * |
66 | * A 32 bit pseudo-random number is generated using a fast |
67 | * algorithm suitable for simulation. This algorithm is NOT |
68 | * considered safe for cryptographic use. |
69 | */ |
70 | u32 random32(void) |
71 | { |
72 | unsigned long r; |
73 | struct rnd_state *state = &get_cpu_var(net_rand_state); |
74 | r = prandom32(state); |
75 | put_cpu_var(state); |
76 | return r; |
77 | } |
78 | EXPORT_SYMBOL(random32); |
79 | |
80 | /** |
81 | * srandom32 - add entropy to pseudo random number generator |
82 | * @seed: seed value |
83 | * |
84 | * Add some additional seeding to the random32() pool. |
85 | */ |
86 | void srandom32(u32 entropy) |
87 | { |
88 | int i; |
89 | /* |
90 | * No locking on the CPUs, but then somewhat random results are, well, |
91 | * expected. |
92 | */ |
93 | for_each_possible_cpu (i) { |
94 | struct rnd_state *state = &per_cpu(net_rand_state, i); |
95 | state->s1 = __seed(state->s1 ^ entropy, 1); |
96 | } |
97 | } |
98 | EXPORT_SYMBOL(srandom32); |
99 | |
100 | /* |
101 | * Generate some initially weak seeding values to allow |
102 | * to start the random32() engine. |
103 | */ |
104 | static int __init random32_init(void) |
105 | { |
106 | int i; |
107 | |
108 | for_each_possible_cpu(i) { |
109 | struct rnd_state *state = &per_cpu(net_rand_state,i); |
110 | |
111 | #define LCG(x) ((x) * 69069) /* super-duper LCG */ |
112 | state->s1 = __seed(LCG(i + jiffies), 1); |
113 | state->s2 = __seed(LCG(state->s1), 7); |
114 | state->s3 = __seed(LCG(state->s2), 15); |
115 | |
116 | /* "warm it up" */ |
117 | prandom32(state); |
118 | prandom32(state); |
119 | prandom32(state); |
120 | prandom32(state); |
121 | prandom32(state); |
122 | prandom32(state); |
123 | } |
124 | return 0; |
125 | } |
126 | core_initcall(random32_init); |
127 | |
128 | /* |
129 | * Generate better values after random number generator |
130 | * is fully initialized. |
131 | */ |
132 | static int __init random32_reseed(void) |
133 | { |
134 | int i; |
135 | |
136 | for_each_possible_cpu(i) { |
137 | struct rnd_state *state = &per_cpu(net_rand_state,i); |
138 | u32 seeds[3]; |
139 | |
140 | get_random_bytes(&seeds, sizeof(seeds)); |
141 | state->s1 = __seed(seeds[0], 1); |
142 | state->s2 = __seed(seeds[1], 7); |
143 | state->s3 = __seed(seeds[2], 15); |
144 | |
145 | /* mix it in */ |
146 | prandom32(state); |
147 | } |
148 | return 0; |
149 | } |
150 | late_initcall(random32_reseed); |
151 |
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