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// 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/prandom.h>
#include <linux/sched.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/unaligned.h>
#include <kunit/visibility.h>
/**
* 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 get_random_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_bytes_state - get the requested number of pseudo-random bytes
*
* @state: pointer to state structure holding seeded state.
* @buf: where to copy the pseudo-random bytes to
* @bytes: the requested number of bytes
*
* This is used for pseudo-randomness with no outside seeding.
* For more random results, use get_random_bytes().
*/
void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
{
u8 *ptr = buf;
while (bytes >= sizeof(u32)) {
put_unaligned(prandom_u32_state(state), (u32 *) ptr);
ptr += sizeof(u32);
bytes -= sizeof(u32);
}
if (bytes > 0) {
u32 rem = prandom_u32_state(state);
do {
*ptr++ = (u8) rem;
bytes--;
rem >>= BITS_PER_BYTE;
} while (bytes > 0);
}
}
EXPORT_SYMBOL(prandom_bytes_state);
/*
* Only declared here so that it has a prototype when made
* non-static for KUnit testing (avoids -Wmissing-prototypes).
*/
#if IS_ENABLED(CONFIG_KUNIT)
void prandom_warmup(struct rnd_state *state);
#endif
VISIBLE_IF_KUNIT void prandom_warmup(struct rnd_state *state)
{
/* Calling RNG ten times to satisfy recurrence condition */
prandom_u32_state(state);
prandom_u32_state(state);
prandom_u32_state(state);
prandom_u32_state(state);
prandom_u32_state(state);
prandom_u32_state(state);
prandom_u32_state(state);
prandom_u32_state(state);
prandom_u32_state(state);
prandom_u32_state(state);
}
EXPORT_SYMBOL_IF_KUNIT(prandom_warmup);
void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
{
int i;
for_each_possible_cpu(i) {
struct rnd_state *state = per_cpu_ptr(pcpu_state, i);
u32 seeds[4];
get_random_bytes(&seeds, sizeof(seeds));
state->s1 = __seed(seeds[0], 2U);
state->s2 = __seed(seeds[1], 8U);
state->s3 = __seed(seeds[2], 16U);
state->s4 = __seed(seeds[3], 128U);
prandom_warmup(state);
}
}
EXPORT_SYMBOL(prandom_seed_full_state);
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