LXR linux/lib/random32.c

   1/*
   2  This is a maximally equidistributed combined Tausworthe generator
   3  based on code from GNU Scientific Library 1.5 (30 Jun 2004)
   4
   5   x_n = (s1_n ^ s2_n ^ s3_n)
   6
   7   s1_{n+1} = (((s1_n & 4294967294) <<12) ^ (((s1_n <<13) ^ s1_n) >>19))
   8   s2_{n+1} = (((s2_n & 4294967288) << 4) ^ (((s2_n << 2) ^ s2_n) >>25))
   9   s3_{n+1} = (((s3_n & 4294967280) <<17) ^ (((s3_n << 3) ^ s3_n) >>11))
  10
  11   The period of this generator is about 2^88.
  12
  13   From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
  14   Generators", Mathematics of Computation, 65, 213 (1996), 203--213.
  15
  16   This is available on the net from L'Ecuyer's home page,
  17
  18   http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
  19   ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
  20
  21   There is an erratum in the paper "Tables of Maximally
  22   Equidistributed Combined LFSR Generators", Mathematics of
  23   Computation, 68, 225 (1999), 261--269:
  24   http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
  25
  26        ... the k_j most significant bits of z_j must be non-
  27        zero, for each j. (Note: this restriction also applies to the
  28        computer code given in [4], but was mistakenly not mentioned in
  29        that paper.)
  30
  31   This affects the seeding procedure by imposing the requirement
  32   s1 > 1, s2 > 7, s3 > 15.
  33
  34*/
  35
  36#include <linux/types.h>
  37#include <linux/percpu.h>
  38#include <linux/module.h>
  39#include <linux/jiffies.h>
  40#include <linux/random.h>
  41
  42struct rnd_state {
  43        u32 s1, s2, s3;
  44};
  45
  46static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
  47
  48static u32 __random32(struct rnd_state *state)
  49{
  50#define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b)
  51
  52        state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12);
  53        state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4);
  54        state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17);
  55
  56        return (state->s1 ^ state->s2 ^ state->s3);
  57}
  58
  59static void __set_random32(struct rnd_state *state, unsigned long s)
  60{
  61        if (s == 0)
  62                s = 1;      /* default seed is 1 */
  63
  64#define LCG(n) (69069 * n)
  65        state->s1 = LCG(s);
  66        state->s2 = LCG(state->s1);
  67        state->s3 = LCG(state->s2);
  68
  69        /* "warm it up" */
  70        __random32(state);
  71        __random32(state);
  72        __random32(state);
  73        __random32(state);
  74        __random32(state);
  75        __random32(state);
  76}
  77
  78/**
  79 *      random32 - pseudo random number generator
  80 *
  81 *      A 32 bit pseudo-random number is generated using a fast
  82 *      algorithm suitable for simulation. This algorithm is NOT
  83 *      considered safe for cryptographic use.
  84 */
  85u32 random32(void)
  86{
  87        unsigned long r;
  88        struct rnd_state *state = &get_cpu_var(net_rand_state);
  89        r = __random32(state);
  90        put_cpu_var(state);
  91        return r;
  92}
  93EXPORT_SYMBOL(random32);
  94
  95/**
  96 *      srandom32 - add entropy to pseudo random number generator
  97 *      @seed: seed value
  98 *
  99 *      Add some additional seeding to the random32() pool.
 100 *      Note: this pool is per cpu so it only affects current CPU.
 101 */
 102void srandom32(u32 entropy)
 103{
 104        struct rnd_state *state = &get_cpu_var(net_rand_state);
 105        __set_random32(state, state->s1 ^ entropy);
 106        put_cpu_var(state);
 107}
 108EXPORT_SYMBOL(srandom32);
 109
 110/*
 111 *      Generate some initially weak seeding values to allow
 112 *      to start the random32() engine.
 113 */
 114static int __init random32_init(void)
 115{
 116        int i;
 117
 118        for_each_possible_cpu(i) {
 119                struct rnd_state *state = &per_cpu(net_rand_state,i);
 120                __set_random32(state, i + jiffies);
 121        }
 122        return 0;
 123}
 124core_initcall(random32_init);
 125
 126/*
 127 *      Generate better values after random number generator
 128 *      is fully initalized.
 129 */
 130static int __init random32_reseed(void)
 131{
 132        int i;
 133        unsigned long seed;
 134
 135        for_each_possible_cpu(i) {
 136                struct rnd_state *state = &per_cpu(net_rand_state,i);
 137
 138                get_random_bytes(&seed, sizeof(seed));
 139                __set_random32(state, seed);
 140        }
 141        return 0;
 142}
 143late_initcall(random32_reseed);
 144