#include <config.h>
#include <stdlib.h>
#include <gsl_rng.h>

/* This is the RANMAR lagged fibonacci generator of Marsaglia, Zaman
   and Tsang.  The sequence is a series of 24-bit integers, x_n,

   x_n = (y_n - c_n + 2^24) mod 2^24

   where,

   y_n = (y_{n-97) - y_{n-33} + 2^24) mod 2^24
   c_n = (c_{n-1} - 7654321 + 2^24 - 3) mod (2^24 - 3)

   The period of this generator is 2^144.

   The generator provides about 900 million different subsequences
   each of length O(10^30). Thus each seed up to 900,000,000 gives an
   independent sequence.

   Although it was good in its day this generator now has known
   statistical defects and has been superseded by RANLUX.

   From: F. James, "A Review of Pseudorandom number generators",
   Computer Physics Communications 60, 329 (1990).

   G. Marsaglia, A. Zaman and W.W. Tsang, Stat. Prob. Lett. 9, 35 (1990)  */

inline unsigned long int ranmar_get (void *vstate);
double ranmar_get_double (void *vstate);
void ranmar_set_impl (void *state, unsigned long int s, unsigned int luxury);
void ranmar_set (void *state, unsigned long int s);
void ranmar389_set (void *state, unsigned long int s);

static const unsigned long int two24 = 16777216;	/* 2^24 */

typedef struct
  {
    unsigned int i;
    unsigned int j;
    long int carry;
    unsigned long int u[97];
  }
ranmar_state_t;

inline unsigned long int
ranmar_get (void *vstate)
{
  ranmar_state_t *state = (ranmar_state_t *) vstate;

  unsigned int i = state->i;
  unsigned int j = state->j;
  long int carry = state->carry;

  long int delta = state->u[i] - state->u[j];

  if (delta < 0)
    delta += two24 ;
  
  state->u[i] = delta;

  if (i == 0)
    {
      i = 96;
    }
  else
    {
      i--;
    }

  state->i = i;

  if (j == 0)
    {
      j = 96;
    }
  else
    {
      j--;
    }

  state->j = j;

  carry += - 7654321 ;
  
  if (carry < 0)
    carry += two24 - 3;
  
  state->carry = carry ;

  delta += - carry ;
  
  if (delta < 0)
    delta += two24 ;

  return delta;
}

double
ranmar_get_double (void *vstate)
{
  return ranmar_get (vstate) / 16777216.0 ;
}

void
ranmar_set (void *vstate, unsigned long int s)
{
  ranmar_state_t *state = (ranmar_state_t *) vstate;
  
  unsigned long int ij = s / 30082 ;
  unsigned long int kl = s % 30082 ;
  
  int i = (ij / 177) % 177 + 2 ;
  int j = (ij % 177) + 2 ;
  int k = (kl / 169) % 178 + 1 ;
  int l = (kl % 169) ;

  int a, b;
  
  for (a = 0; a < 97; a++)
    {
      unsigned long int sum = 0 ;
      unsigned long int t = two24 ;

      for (b = 0; b < 24; b++)
	{
	  unsigned long int m = (((i * j) % 179) * k) % 179 ;
	  i = j ;
	  j = k ;
	  k = m ;
	  l = (53 * l + 1) % 169 ;
	  t >>= 1 ;
	  
	  if ((l * m) % 64 >= 32)
	    sum += t ;
	}

      state->u[a] = sum ;
    }

  state->i = 96;
  state->j = 32;
  state->carry = 362436 ;

}

static const gsl_rng_type ranmar_type =
{"ranmar",			/* name */
 0x00ffffffUL,			/* RAND_MAX */
 0,				/* RAND_MIN */
 sizeof (ranmar_state_t),
 &ranmar_set,
 &ranmar_get,
 &ranmar_get_double};

const gsl_rng_type *gsl_rng_ranmar = &ranmar_type;