/* rng/fishman20.c

 * 

 * 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.

 */

/*

 * This generator is taken from

 *

 * Donald E. Knuth

 * The Art of Computer Programming

 * Volume 2

 * Third Edition

 * Addison-Wesley

 * Page 108

 *

 * It is called "Fishman"

 *

 * This implementation copyright (C) 2001 Carlo Perassi

 * and (C) 2003 Heiko Bauke.

 */

#include <config.h>

#include <stdlib.h>

#include <gsl/gsl_rng.h>

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

static double ran_get_double (void *vstate);

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

static const long int m = 2147483647, a = 48271, q = 44488, r = 3399;

typedef struct

{

  unsigned long int x;

}

ran_state_t;

static inline unsigned long int

ran_get (void *vstate)

{

  ran_state_t *state = (ran_state_t *) vstate;

  const unsigned long int x = state->x;

  const long int h = x / q;

  const long int t = a * (x - h * q) - h * r;

  if (t < 0)

    {

      state->x = t + m;

    }

  else

    {

      state->x = t;

    }

  return state->x;

}

static double

ran_get_double (void *vstate)

{

  ran_state_t *state = (ran_state_t *) vstate;

  return ran_get (state) / 2147483647.0;

}

static void

ran_set (void *vstate, unsigned long int s)

{

  ran_state_t *state = (ran_state_t *) vstate;

  if ((s%m) == 0)

    s = 1;                      /* default seed is 1 */

  state->x = s & m;

  return;

}

static const gsl_rng_type ran_type = {

  "fishman20",                  /* name */

  2147483646,                   /* RAND_MAX */

  1,                            /* RAND_MIN */

  sizeof (ran_state_t),

  &ran_set,

  &ran_get,

  &ran_get_double

};

const gsl_rng_type *gsl_rng_fishman20 = &ran_type;