2 This is a maximally equidistributed combined Tausworthe generator
3 based on code from GNU Scientific Library 1.5 (30 Jun 2004)
7 x_n = (s1_n ^ s2_n ^ s3_n ^ s4_n)
9 s1_{n+1} = (((s1_n & 4294967294) << 18) ^ (((s1_n << 6) ^ s1_n) >> 13))
10 s2_{n+1} = (((s2_n & 4294967288) << 2) ^ (((s2_n << 2) ^ s2_n) >> 27))
11 s3_{n+1} = (((s3_n & 4294967280) << 7) ^ (((s3_n << 13) ^ s3_n) >> 21))
12 s4_{n+1} = (((s4_n & 4294967168) << 13) ^ (((s4_n << 3) ^ s4_n) >> 12))
14 The period of this generator is about 2^113 (see erratum paper).
16 From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
17 Generators", Mathematics of Computation, 65, 213 (1996), 203--213:
18 http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
19 ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
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
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
31 This affects the seeding procedure by imposing the requirement
32 s1 > 1, s2 > 7, s3 > 15, s4 > 127.
36 #include <linux/types.h>
37 #include <linux/percpu.h>
38 #include <linux/export.h>
39 #include <linux/jiffies.h>
40 #include <linux/random.h>
42 static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
45 * prandom_u32_state - seeded pseudo-random number generator.
46 * @state: pointer to state structure holding seeded state.
48 * This is used for pseudo-randomness with no outside seeding.
49 * For more random results, use prandom_u32().
51 u32 prandom_u32_state(struct rnd_state *state)
53 #define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b)
55 state->s1 = TAUSWORTHE(state->s1, 6U, 13U, 4294967294U, 18U);
56 state->s2 = TAUSWORTHE(state->s2, 2U, 27U, 4294967288U, 2U);
57 state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U, 7U);
58 state->s4 = TAUSWORTHE(state->s4, 3U, 12U, 4294967168U, 13U);
60 return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
62 EXPORT_SYMBOL(prandom_u32_state);
65 * prandom_u32 - pseudo random number generator
67 * A 32 bit pseudo-random number is generated using a fast
68 * algorithm suitable for simulation. This algorithm is NOT
69 * considered safe for cryptographic use.
74 struct rnd_state *state = &get_cpu_var(net_rand_state);
75 r = prandom_u32_state(state);
79 EXPORT_SYMBOL(prandom_u32);
82 * prandom_bytes_state - get the requested number of pseudo-random bytes
84 * @state: pointer to state structure holding seeded state.
85 * @buf: where to copy the pseudo-random bytes to
86 * @bytes: the requested number of bytes
88 * This is used for pseudo-randomness with no outside seeding.
89 * For more random results, use prandom_bytes().
91 void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes)
93 unsigned char *p = buf;
96 for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) {
97 u32 random = prandom_u32_state(state);
100 for (j = 0; j < sizeof(u32); j++) {
102 random >>= BITS_PER_BYTE;
106 u32 random = prandom_u32_state(state);
108 for (; i < bytes; i++) {
110 random >>= BITS_PER_BYTE;
114 EXPORT_SYMBOL(prandom_bytes_state);
117 * prandom_bytes - get the requested number of pseudo-random bytes
118 * @buf: where to copy the pseudo-random bytes to
119 * @bytes: the requested number of bytes
121 void prandom_bytes(void *buf, int bytes)
123 struct rnd_state *state = &get_cpu_var(net_rand_state);
125 prandom_bytes_state(state, buf, bytes);
128 EXPORT_SYMBOL(prandom_bytes);
130 static void prandom_warmup(struct rnd_state *state)
132 /* Calling RNG ten times to satify recurrence condition */
133 prandom_u32_state(state);
134 prandom_u32_state(state);
135 prandom_u32_state(state);
136 prandom_u32_state(state);
137 prandom_u32_state(state);
138 prandom_u32_state(state);
139 prandom_u32_state(state);
140 prandom_u32_state(state);
141 prandom_u32_state(state);
142 prandom_u32_state(state);
146 * prandom_seed - add entropy to pseudo random number generator
149 * Add some additional seeding to the prandom pool.
151 void prandom_seed(u32 entropy)
155 * No locking on the CPUs, but then somewhat random results are, well,
158 for_each_possible_cpu (i) {
159 struct rnd_state *state = &per_cpu(net_rand_state, i);
161 state->s1 = __seed(state->s1 ^ entropy, 2U);
162 prandom_warmup(state);
165 EXPORT_SYMBOL(prandom_seed);
168 * Generate some initially weak seeding values to allow
169 * to start the prandom_u32() engine.
171 static int __init prandom_init(void)
175 for_each_possible_cpu(i) {
176 struct rnd_state *state = &per_cpu(net_rand_state,i);
178 #define LCG(x) ((x) * 69069U) /* super-duper LCG */
179 state->s1 = __seed(LCG((i + jiffies) ^ random_get_entropy()), 2U);
180 state->s2 = __seed(LCG(state->s1), 8U);
181 state->s3 = __seed(LCG(state->s2), 16U);
182 state->s4 = __seed(LCG(state->s3), 128U);
184 prandom_warmup(state);
188 core_initcall(prandom_init);
190 static void __prandom_timer(unsigned long dontcare);
191 static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0);
193 static void __prandom_timer(unsigned long dontcare)
197 get_random_bytes(&entropy, sizeof(entropy));
198 prandom_seed(entropy);
199 /* reseed every ~60 seconds, in [40 .. 80) interval with slack */
200 seed_timer.expires = jiffies + (40 * HZ + (prandom_u32() % (40 * HZ)));
201 add_timer(&seed_timer);
204 static void prandom_start_seed_timer(void)
206 set_timer_slack(&seed_timer, HZ);
207 seed_timer.expires = jiffies + 40 * HZ;
208 add_timer(&seed_timer);
212 * Generate better values after random number generator
213 * is fully initialized.
215 static void __prandom_reseed(bool late)
219 static bool latch = false;
220 static DEFINE_SPINLOCK(lock);
222 /* only allow initial seeding (late == false) once */
223 spin_lock_irqsave(&lock, flags);
228 for_each_possible_cpu(i) {
229 struct rnd_state *state = &per_cpu(net_rand_state,i);
232 get_random_bytes(&seeds, sizeof(seeds));
233 state->s1 = __seed(seeds[0], 2U);
234 state->s2 = __seed(seeds[1], 8U);
235 state->s3 = __seed(seeds[2], 16U);
236 state->s4 = __seed(seeds[3], 128U);
238 prandom_warmup(state);
241 spin_unlock_irqrestore(&lock, flags);
244 void prandom_reseed_late(void)
246 __prandom_reseed(true);
249 static int __init prandom_reseed(void)
251 __prandom_reseed(false);
252 prandom_start_seed_timer();
255 late_initcall(prandom_reseed);