xref: /openbmc/linux/lib/random32.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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 struct rnd_state {
43 	u32 s1, s2, s3;
44 };
45 
46 static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
47 
48 static u32 __random32(struct rnd_state *state)
49 {
50 #define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b)
51 
52 	state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12);
53 	state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4);
54 	state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17);
55 
56 	return (state->s1 ^ state->s2 ^ state->s3);
57 }
58 
59 static void __set_random32(struct rnd_state *state, unsigned long s)
60 {
61 	if (s == 0)
62 		s = 1;      /* default seed is 1 */
63 
64 #define LCG(n) (69069 * n)
65 	state->s1 = LCG(s);
66 	state->s2 = LCG(state->s1);
67 	state->s3 = LCG(state->s2);
68 
69 	/* "warm it up" */
70 	__random32(state);
71 	__random32(state);
72 	__random32(state);
73 	__random32(state);
74 	__random32(state);
75 	__random32(state);
76 }
77 
78 /**
79  *	random32 - pseudo random number generator
80  *
81  *	A 32 bit pseudo-random number is generated using a fast
82  *	algorithm suitable for simulation. This algorithm is NOT
83  *	considered safe for cryptographic use.
84  */
85 u32 random32(void)
86 {
87 	unsigned long r;
88 	struct rnd_state *state = &get_cpu_var(net_rand_state);
89 	r = __random32(state);
90 	put_cpu_var(state);
91 	return r;
92 }
93 EXPORT_SYMBOL(random32);
94 
95 /**
96  *	srandom32 - add entropy to pseudo random number generator
97  *	@seed: seed value
98  *
99  *	Add some additional seeding to the random32() pool.
100  *	Note: this pool is per cpu so it only affects current CPU.
101  */
102 void srandom32(u32 entropy)
103 {
104 	struct rnd_state *state = &get_cpu_var(net_rand_state);
105 	__set_random32(state, state->s1 ^ entropy);
106 	put_cpu_var(state);
107 }
108 EXPORT_SYMBOL(srandom32);
109 
110 /*
111  *	Generate some initially weak seeding values to allow
112  *	to start the random32() engine.
113  */
114 static int __init random32_init(void)
115 {
116 	int i;
117 
118 	for_each_possible_cpu(i) {
119 		struct rnd_state *state = &per_cpu(net_rand_state,i);
120 		__set_random32(state, i + jiffies);
121 	}
122 	return 0;
123 }
124 core_initcall(random32_init);
125 
126 /*
127  *	Generate better values after random number generator
128  *	is fully initalized.
129  */
130 static int __init random32_reseed(void)
131 {
132 	int i;
133 	unsigned long seed;
134 
135 	for_each_possible_cpu(i) {
136 		struct rnd_state *state = &per_cpu(net_rand_state,i);
137 
138 		get_random_bytes(&seed, sizeof(seed));
139 		__set_random32(state, seed);
140 	}
141 	return 0;
142 }
143 late_initcall(random32_reseed);
144