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 /* 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 #include #include #include #include struct rnd_state { u32 s1, s2, s3; }; static DEFINE_PER_CPU(struct rnd_state, net_rand_state); static u32 __random32(struct rnd_state *state) { #define TAUSWORTHE(s,a,b,c,d) ((s&c)<>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); } /* * Handle minimum values for seeds */ static inline u32 __seed(u32 x, u32 m) { return (x < m) ? x + m : x; } /** * 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 = __random32(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" */ __random32(state); __random32(state); __random32(state); __random32(state); __random32(state); __random32(state); } return 0; } core_initcall(random32_init); /* * Generate better values after random number generator * is fully initalized. */ 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 */ __random32(state); } return 0; } late_initcall(random32_reseed);