/*  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/export.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);