155 lines
3.8 KiB
C
155 lines
3.8 KiB
C
/*
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This is a maximally equidistributed combined Tausworthe generator
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based on code from GNU Scientific Library 1.5 (30 Jun 2004)
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x_n = (s1_n ^ s2_n ^ s3_n)
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s1_{n+1} = (((s1_n & 4294967294) <<12) ^ (((s1_n <<13) ^ s1_n) >>19))
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s2_{n+1} = (((s2_n & 4294967288) << 4) ^ (((s2_n << 2) ^ s2_n) >>25))
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s3_{n+1} = (((s3_n & 4294967280) <<17) ^ (((s3_n << 3) ^ s3_n) >>11))
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The period of this generator is about 2^88.
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From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
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Generators", Mathematics of Computation, 65, 213 (1996), 203--213.
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This is available on the net from L'Ecuyer's home page,
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http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
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ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
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There is an erratum in the paper "Tables of Maximally
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Equidistributed Combined LFSR Generators", Mathematics of
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Computation, 68, 225 (1999), 261--269:
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http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
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... the k_j most significant bits of z_j must be non-
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zero, for each j. (Note: this restriction also applies to the
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computer code given in [4], but was mistakenly not mentioned in
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that paper.)
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This affects the seeding procedure by imposing the requirement
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s1 > 1, s2 > 7, s3 > 15.
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*/
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#include <linux/types.h>
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#include <linux/percpu.h>
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#include <linux/module.h>
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#include <linux/jiffies.h>
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#include <linux/random.h>
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struct rnd_state {
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u32 s1, s2, s3;
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};
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static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
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static u32 __random32(struct rnd_state *state)
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{
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#define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b)
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state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12);
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state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4);
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state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17);
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return (state->s1 ^ state->s2 ^ state->s3);
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}
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/*
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* Handle minimum values for seeds
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*/
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static inline u32 __seed(u32 x, u32 m)
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{
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return (x < m) ? x + m : x;
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}
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/**
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* random32 - pseudo random number generator
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*
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* A 32 bit pseudo-random number is generated using a fast
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* algorithm suitable for simulation. This algorithm is NOT
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* considered safe for cryptographic use.
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*/
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u32 random32(void)
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{
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unsigned long r;
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struct rnd_state *state = &get_cpu_var(net_rand_state);
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r = __random32(state);
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put_cpu_var(state);
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return r;
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}
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EXPORT_SYMBOL(random32);
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/**
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* srandom32 - add entropy to pseudo random number generator
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* @seed: seed value
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*
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* Add some additional seeding to the random32() pool.
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*/
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void srandom32(u32 entropy)
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{
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int i;
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/*
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* No locking on the CPUs, but then somewhat random results are, well,
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* expected.
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*/
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for_each_possible_cpu (i) {
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struct rnd_state *state = &per_cpu(net_rand_state, i);
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state->s1 = __seed(state->s1 ^ entropy, 1);
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}
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}
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EXPORT_SYMBOL(srandom32);
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/*
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* Generate some initially weak seeding values to allow
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* to start the random32() engine.
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*/
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static int __init random32_init(void)
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{
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int i;
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for_each_possible_cpu(i) {
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struct rnd_state *state = &per_cpu(net_rand_state,i);
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#define LCG(x) ((x) * 69069) /* super-duper LCG */
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state->s1 = __seed(LCG(i + jiffies), 1);
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state->s2 = __seed(LCG(state->s1), 7);
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state->s3 = __seed(LCG(state->s2), 15);
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/* "warm it up" */
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__random32(state);
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__random32(state);
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__random32(state);
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__random32(state);
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__random32(state);
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__random32(state);
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}
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return 0;
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}
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core_initcall(random32_init);
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/*
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* Generate better values after random number generator
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* is fully initalized.
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*/
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static int __init random32_reseed(void)
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{
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int i;
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for_each_possible_cpu(i) {
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struct rnd_state *state = &per_cpu(net_rand_state,i);
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u32 seeds[3];
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get_random_bytes(&seeds, sizeof(seeds));
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state->s1 = __seed(seeds[0], 1);
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state->s2 = __seed(seeds[1], 7);
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state->s3 = __seed(seeds[2], 15);
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/* mix it in */
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__random32(state);
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}
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return 0;
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}
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late_initcall(random32_reseed);
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