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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 <linux/types.h>

#include <linux/percpu.h>

#include <linux/module.h>

#include <linux/jiffies.h>

#include <linux/random.h>

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)<<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);

}

static void __set_random32(struct rnd_state *state, unsigned long s)

{

        if (s == 0)

                s = 1;      /* default seed is 1 */

#define LCG(n) (69069 * n)

        state->s1 = LCG(s);

        state->s2 = LCG(state->s1);

        state->s3 = LCG(state->s2);

        /* "warm it up" */

        __random32(state);

        __random32(state);

        __random32(state);

        __random32(state);

        __random32(state);

        __random32(state);

}

/**

 *      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.

 *      Note: this pool is per cpu so it only affects current CPU.

 */

void srandom32(u32 entropy)

{

        struct rnd_state *state = &get_cpu_var(net_rand_state);

        __set_random32(state, state->s1 ^ entropy);

        put_cpu_var(state);

}

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);

                __set_random32(state, i + jiffies);

        }

        return 0;

}

core_initcall(random32_init);

/*

 *      Generate better values after random number generator

 *      is fully initalized.

 */

static int __init random32_reseed(void)

{

        int i;

        unsigned long seed;

        for_each_possible_cpu(i) {

                struct rnd_state *state = &per_cpu(net_rand_state,i);

                get_random_bytes(&seed, sizeof(seed));

                __set_random32(state, seed);

        }

        return 0;

}

late_initcall(random32_reseed);