This commit was manufactured by cvs2svn to create branch 'vserver'.

[linux-2.6.git] / lib / random32.c

diff --git a/lib/random32.c b/lib/random32.c
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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);