/* rng/zuf.c

 * 

 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 James Theiler, Brian Gough

 * 

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 3 of the License, or (at

 * your option) any later version.

 * 

 * This program is distributed in the hope that it will be useful, but

 * WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * General Public License for more details.

 * 

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

 */

#include <config.h>

#include <stdlib.h>

#include <gsl/gsl_rng.h>

/* It is crucial that m == n-273 mod 607 at all times;

   For speed of execution, however, this is never enforced.

   Instead is is set in the initializer: note 607-273=334

   Note also that the state.u[607] is not initialized */

static inline unsigned long int zuf_get (void *vstate);

static double zuf_get_double (void *vstate);

static void zuf_set (void *state, unsigned long int s);

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

typedef struct

  {

    int n;

    unsigned long int u[607];

  }

zuf_state_t;

/* The zufall package was implemented with float's, which is to say 24

   bits of precision.  Since I'm using long's instead, my RANDMAX

   reflects this. */

static inline unsigned long int

zuf_get (void *vstate)

{

  zuf_state_t *state = (zuf_state_t *) vstate;

  const int n = state->n;

  const int m = (n - 273 + 607) % 607;

  unsigned long int t = state->u[n] + state->u[m];

  while (t > zuf_randmax)

    t -= zuf_randmax;

  state->u[n] = t;

  if (n == 606)

    {

      state->n = 0;

    }

  else

    {

      state->n = n + 1;

    }

  return t;

}

static double

zuf_get_double (void *vstate)

{

  return zuf_get (vstate) / 16777216.0 ;

}

static void

zuf_set (void *vstate, unsigned long int s)

{

  /* A very elaborate seeding procedure is provided with the

     zufall package; this is virtually a copy of that procedure */

  /* Initialized data */

  long int kl = 9373;

  long int ij = 1802;

  /* Local variables */

  long int i, j, k, l, m;

  double x, y;

  long int ii, jj;

  zuf_state_t *state = (zuf_state_t *) vstate;

  state->n = 0;

/*  generates initial seed buffer by linear congruential */

/*  method. Taken from Marsaglia, FSU report FSU-SCRI-87-50 */

/*  variable seed should be 0 < seed <31328 */

  if (s == 0)

    s = 1802;   /* default seed is 1802 */

  ij = s;

  i = ij / 177 % 177 + 2;

  j = ij % 177 + 2;

  k = kl / 169 % 178 + 1;

  l = kl % 169;

  for (ii = 0; ii < 607; ++ii)

    {

      x = 0.0;

      y = 0.5;

      /* 24 bits?? */

      for (jj = 1; jj <= 24; ++jj)

        {

          m = i * j % 179 * k % 179;

          i = j;

          j = k;

          k = m;

          l = (l * 53 + 1) % 169;

          if (l * m % 64 >= 32)

            {

              x += y;

            }

          y *= 0.5;

        }

      state->u[ii] = (unsigned long int) (x * zuf_randmax);

    }

}

static const gsl_rng_type zuf_type =

{"zuf",                         /* name */

 0x00ffffffUL,                  /* RAND_MAX */

 0,                             /* RAND_MIN */

 sizeof (zuf_state_t),

 &zuf_set,

 &zuf_get,

 &zuf_get_double};

const gsl_rng_type *gsl_rng_zuf = &zuf_type;