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Diffstat (limited to 'lib/random32.c')
-rw-r--r-- | lib/random32.c | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/lib/random32.c b/lib/random32.c new file mode 100644 index 00000000..fc3545a3 --- /dev/null +++ b/lib/random32.c @@ -0,0 +1,150 @@ +/* + This is a maximally equidistributed combined Tausworthe generator + based on code from GNU Scientific Library 1.5 (30 Jun 2004) + + x_n = (s1_n ^ s2_n ^ s3_n) + + s1_{n+1} = (((s1_n & 4294967294) <<12) ^ (((s1_n <<13) ^ s1_n) >>19)) + s2_{n+1} = (((s2_n & 4294967288) << 4) ^ (((s2_n << 2) ^ s2_n) >>25)) + s3_{n+1} = (((s3_n & 4294967280) <<17) ^ (((s3_n << 3) ^ s3_n) >>11)) + + The period of this generator is about 2^88. + + From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe + Generators", Mathematics of Computation, 65, 213 (1996), 203--213. + + This is available on the net from L'Ecuyer's home page, + + http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps + ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps + + There is an erratum in the paper "Tables of Maximally + Equidistributed Combined LFSR Generators", Mathematics of + Computation, 68, 225 (1999), 261--269: + http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps + + ... the k_j most significant bits of z_j must be non- + zero, for each j. (Note: this restriction also applies to the + computer code given in [4], but was mistakenly not mentioned in + that paper.) + + This affects the seeding procedure by imposing the requirement + s1 > 1, s2 > 7, s3 > 15. + +*/ + +#include <linux/types.h> +#include <linux/percpu.h> +#include <linux/module.h> +#include <linux/jiffies.h> +#include <linux/random.h> + +static DEFINE_PER_CPU(struct rnd_state, net_rand_state); + +/** + * prandom32 - seeded pseudo-random number generator. + * @state: pointer to state structure holding seeded state. + * + * This is used for pseudo-randomness with no outside seeding. + * For more random results, use random32(). + */ +u32 prandom32(struct rnd_state *state) +{ +#define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b) + + state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12); + state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4); + state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17); + + return (state->s1 ^ state->s2 ^ state->s3); +} +EXPORT_SYMBOL(prandom32); + +/** + * random32 - pseudo random number generator + * + * A 32 bit pseudo-random number is generated using a fast + * algorithm suitable for simulation. This algorithm is NOT + * considered safe for cryptographic use. + */ +u32 random32(void) +{ + unsigned long r; + struct rnd_state *state = &get_cpu_var(net_rand_state); + r = prandom32(state); + put_cpu_var(state); + return r; +} +EXPORT_SYMBOL(random32); + +/** + * srandom32 - add entropy to pseudo random number generator + * @seed: seed value + * + * Add some additional seeding to the random32() pool. + */ +void srandom32(u32 entropy) +{ + int i; + /* + * No locking on the CPUs, but then somewhat random results are, well, + * expected. + */ + for_each_possible_cpu (i) { + struct rnd_state *state = &per_cpu(net_rand_state, i); + state->s1 = __seed(state->s1 ^ entropy, 1); + } +} +EXPORT_SYMBOL(srandom32); + +/* + * Generate some initially weak seeding values to allow + * to start the random32() engine. + */ +static int __init random32_init(void) +{ + int i; + + for_each_possible_cpu(i) { + struct rnd_state *state = &per_cpu(net_rand_state,i); + +#define LCG(x) ((x) * 69069) /* super-duper LCG */ + state->s1 = __seed(LCG(i + jiffies), 1); + state->s2 = __seed(LCG(state->s1), 7); + state->s3 = __seed(LCG(state->s2), 15); + + /* "warm it up" */ + prandom32(state); + prandom32(state); + prandom32(state); + prandom32(state); + prandom32(state); + prandom32(state); + } + return 0; +} +core_initcall(random32_init); + +/* + * Generate better values after random number generator + * is fully initialized. + */ +static int __init random32_reseed(void) +{ + int i; + + for_each_possible_cpu(i) { + struct rnd_state *state = &per_cpu(net_rand_state,i); + u32 seeds[3]; + + get_random_bytes(&seeds, sizeof(seeds)); + state->s1 = __seed(seeds[0], 1); + state->s2 = __seed(seeds[1], 7); + state->s3 = __seed(seeds[2], 15); + + /* mix it in */ + prandom32(state); + } + return 0; +} +late_initcall(random32_reseed); |