/*
    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);