/*
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>
static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
/**
* 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)
{
unsigned long r;
struct rnd_state *state = &get_cpu_var(net_rand_state);
r = prandom_u32_state(state);
put_cpu_var(state);
return r;
}
EXPORT_SYMBOL(prandom_u32);
/*
* 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 prandom_bytes().
*/
void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes)
{
unsigned char *p = buf;
int i;
for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) {
u32 random = prandom_u32_state(state);
int j;
for (j = 0; j < sizeof(u32); j++) {
p[i + j] = random;
random >>= BITS_PER_BYTE;
}
}
if (i < bytes) {
u32 random = prandom_u32_state(state);
for (; i < bytes; i++) {
p[i] = random;
random >>= BITS_PER_BYTE;
}
}
}
EXPORT_SYMBOL(prandom_bytes_state);
/**
* prandom_bytes - get the requested number of pseudo-random bytes
* @buf: where to copy the pseudo-random bytes to
* @bytes: the requested number of bytes
*/
void prandom_bytes(void *buf, int bytes)
{
struct rnd_state *state = &get_cpu_var(net_rand_state);
prandom_bytes_state(state, buf, bytes);
put_cpu_var(state);
}
EXPORT_SYMBOL(prandom_bytes);
static void prandom_warmup(struct rnd_state *state)
{
/* Calling RNG ten times to satify 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);
}
/**
* prandom_seed - add entropy to pseudo random number generator
* @seed: seed value
*
* Add some additional seeding to the prandom pool.
*/
void prandom_seed(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, 2U);
prandom_warmup(state);
}
}
EXPORT_SYMBOL(prandom_seed);
/*
* Generate some initially weak seeding values to allow
* to start the prandom_u32() engine.
*/
static int __init prandom_init(void)
{
int i;
for_each_possible_cpu(i) {
struct rnd_state *state = &per_cpu(net_rand_state,i);
#define LCG(x) ((x) * 69069U) /* super-duper LCG */
state->s1 = __seed(LCG((i + jiffies) ^ random_get_entropy()), 2U);
state->s2 = __seed(LCG(state->s1), 8U);
state->s3 = __seed(LCG(state->s2), 16U);
state->s4 = __seed(LCG(state->s3), 128U);
prandom_warmup(state);
}
return 0;
}
core_initcall(prandom_init);
static void __prandom_timer(unsigned long dontcare);
static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0);
static void __prandom_timer(unsigned long dontcare)
{
u32 entropy;
get_random_bytes(&entropy, sizeof(entropy));
prandom_seed(entropy);
/* reseed every ~60 seconds, in [40 .. 80) interval with slack */
seed_timer.expires = jiffies + (40 * HZ + (prandom_u32() % (40 * HZ)));
add_timer(&seed_timer);
}
static void prandom_start_seed_timer(void)
{
set_timer_slack(&seed_timer, HZ);
seed_timer.expires = jiffies + 40 * HZ;
add_timer(&seed_timer);
}
/*
* Generate better values after random number generator
* is fully initialized.
*/
static void __prandom_reseed(bool late)
{
int i;
unsigned long flags;
static bool latch = false;
static DEFINE_SPINLOCK(lock);
/* only allow initial seeding (late == false) once */
spin_lock_irqsave(&lock, flags);
if (latch && !late)
goto out;
latch = true;
for_each_possible_cpu(i) {
struct rnd_state *state = &per_cpu(net_rand_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);
}
out:
spin_unlock_irqrestore(&lock, flags);
}
void prandom_reseed_late(void)
{
__prandom_reseed(true);
}
static int __init prandom_reseed(void)
{
__prandom_reseed(false);
prandom_start_seed_timer();
return 0;
}
late_initcall(prandom_reseed);
