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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> | |
8bc3bcc9 | 38 | #include <linux/export.h> |
f6a57033 | 39 | #include <linux/jiffies.h> |
aaa248f6 SH |
40 | #include <linux/random.h> |
41 | ||
aaa248f6 SH |
42 | static DEFINE_PER_CPU(struct rnd_state, net_rand_state); |
43 | ||
5960164f | 44 | /** |
496f2f93 | 45 | * prandom_u32_state - seeded pseudo-random number generator. |
5960164f JE |
46 | * @state: pointer to state structure holding seeded state. |
47 | * | |
48 | * This is used for pseudo-randomness with no outside seeding. | |
496f2f93 | 49 | * For more random results, use prandom_u32(). |
5960164f | 50 | */ |
496f2f93 | 51 | u32 prandom_u32_state(struct rnd_state *state) |
aaa248f6 SH |
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 | } | |
496f2f93 | 61 | EXPORT_SYMBOL(prandom_u32_state); |
aaa248f6 SH |
62 | |
63 | /** | |
496f2f93 | 64 | * prandom_u32 - pseudo random number generator |
aaa248f6 SH |
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 | */ | |
496f2f93 | 70 | u32 prandom_u32(void) |
aaa248f6 SH |
71 | { |
72 | unsigned long r; | |
73 | struct rnd_state *state = &get_cpu_var(net_rand_state); | |
496f2f93 | 74 | r = prandom_u32_state(state); |
aaa248f6 SH |
75 | put_cpu_var(state); |
76 | return r; | |
77 | } | |
496f2f93 | 78 | EXPORT_SYMBOL(prandom_u32); |
aaa248f6 SH |
79 | |
80 | /** | |
496f2f93 | 81 | * prandom_seed - add entropy to pseudo random number generator |
aaa248f6 SH |
82 | * @seed: seed value |
83 | * | |
496f2f93 | 84 | * Add some additional seeding to the prandom pool. |
aaa248f6 | 85 | */ |
496f2f93 | 86 | void prandom_seed(u32 entropy) |
aaa248f6 | 87 | { |
61407f80 AK |
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); | |
697f8d03 | 95 | state->s1 = __seed(state->s1 ^ entropy, 1); |
61407f80 | 96 | } |
aaa248f6 | 97 | } |
496f2f93 | 98 | EXPORT_SYMBOL(prandom_seed); |
aaa248f6 SH |
99 | |
100 | /* | |
101 | * Generate some initially weak seeding values to allow | |
496f2f93 | 102 | * to start the prandom_u32() engine. |
aaa248f6 | 103 | */ |
496f2f93 | 104 | static int __init prandom_init(void) |
aaa248f6 SH |
105 | { |
106 | int i; | |
107 | ||
108 | for_each_possible_cpu(i) { | |
109 | struct rnd_state *state = &per_cpu(net_rand_state,i); | |
697f8d03 SH |
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" */ | |
496f2f93 AM |
117 | prandom_u32_state(state); |
118 | prandom_u32_state(state); | |
119 | prandom_u32_state(state); | |
120 | prandom_u32_state(state); | |
121 | prandom_u32_state(state); | |
122 | prandom_u32_state(state); | |
aaa248f6 SH |
123 | } |
124 | return 0; | |
125 | } | |
496f2f93 | 126 | core_initcall(prandom_init); |
aaa248f6 SH |
127 | |
128 | /* | |
129 | * Generate better values after random number generator | |
421f91d2 | 130 | * is fully initialized. |
aaa248f6 | 131 | */ |
496f2f93 | 132 | static int __init prandom_reseed(void) |
aaa248f6 SH |
133 | { |
134 | int i; | |
aaa248f6 SH |
135 | |
136 | for_each_possible_cpu(i) { | |
137 | struct rnd_state *state = &per_cpu(net_rand_state,i); | |
697f8d03 SH |
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); | |
aaa248f6 | 144 | |
697f8d03 | 145 | /* mix it in */ |
496f2f93 | 146 | prandom_u32_state(state); |
aaa248f6 SH |
147 | } |
148 | return 0; | |
149 | } | |
496f2f93 | 150 | late_initcall(prandom_reseed); |