linux-imx

// SPDX-License-Identifier: GPL-2.0

/*

 * This is a maximally equidistributed combined Tausworthe generator

 * based on code from GNU Scientific Library 1.5 (30 Jun 2004)

 *

 * lfsr113 version:

 *

 * x_n = (s1_n ^ s2_n ^ s3_n ^ s4_n)

 *

 * s1_{n+1} = (((s1_n & 4294967294) << 18) ^ (((s1_n <<  6) ^ s1_n) >> 13))

 * s2_{n+1} = (((s2_n & 4294967288) <<  2) ^ (((s2_n <<  2) ^ s2_n) >> 27))

 * s3_{n+1} = (((s3_n & 4294967280) <<  7) ^ (((s3_n << 13) ^ s3_n) >> 21))

 * s4_{n+1} = (((s4_n & 4294967168) << 13) ^ (((s4_n <<  3) ^ s4_n) >> 12))

 *

 * The period of this generator is about 2^113 (see erratum paper).

 *

 * From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe

 * Generators", Mathematics of Computation, 65, 213 (1996), 203--213:

 * 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, s4 > 127.

 */

​

#include <linux/types.h>

#include <linux/percpu.h>

#include <linux/export.h>

#include <linux/jiffies.h>

#include <linux/random.h>

#include <linux/sched.h>

#include <asm/unaligned.h>

​

#ifdef CONFIG_RANDOM32_SELFTEST

static void __init prandom_state_selftest(void);

#else

static inline void prandom_state_selftest(void)

{

}

#endif

​

static DEFINE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy;

​

/**

 *  prandom_u32_state - 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 prandom_u32().

 */

u32 prandom_u32_state(struct rnd_state *state)

{

#define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)

    state->s1 = TAUSWORTHE(state->s1,  6U, 13U, 4294967294U, 18U);

    state->s2 = TAUSWORTHE(state->s2,  2U, 27U, 4294967288U,  2U);

    state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U,  7U);

    state->s4 = TAUSWORTHE(state->s4,  3U, 12U, 4294967168U, 13U);

​

    return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);

}

EXPORT_SYMBOL(prandom_u32_state);

​

/**

 *  prandom_u32 - 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 prandom_u32(void)

{

    struct rnd_state *state = &get_cpu_var(net_rand_state);

    u32 res;

​

    res = prandom_u32_state(state);

    put_cpu_var(net_rand_state);

​

    return res;

}

EXPORT_SYMBOL(prandom_u32);

​

/**

 *  prandom_bytes_state - get the requested number of pseudo-random bytes