/* rng/ran1.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>

/* This is an implementation of the algorithm used in Numerical

   Recipe's ran1 generator.  It is MINSTD with a 32-element

   shuffle-box. */

static inline unsigned long int ran1_get (void *vstate);

static double ran1_get_double (void *vstate);

static void ran1_set (void *state, unsigned long int s);

static const long int m = 2147483647, a = 16807, q = 127773, r = 2836;

#define N_SHUFFLE 32

#define N_DIV (1 + 2147483646/N_SHUFFLE)

typedef struct

  {

    unsigned long int x;

    unsigned long int n;

    unsigned long int shuffle[N_SHUFFLE];

  }

ran1_state_t;

static inline unsigned long int

ran1_get (void *vstate)

{

  ran1_state_t *state = (ran1_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;

    }

  {

    unsigned long int j = state->n / N_DIV;

    state->n = state->shuffle[j];

    state->shuffle[j] = state->x;

  }

  return state->n;

}

static double

ran1_get_double (void *vstate)

{

  float x_max = 1 - 1.2e-7f ; /* Numerical Recipes version of 1-FLT_EPS */

  float x = ran1_get (vstate) / 2147483647.0f ;

  if (x > x_max) 

    return x_max ;

  return x ;

}

static void

ran1_set (void *vstate, unsigned long int s)

{

  ran1_state_t *state = (ran1_state_t *) vstate;

  int i;

  if (s == 0)

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

  for (i = 0; i < 8; i++)

    {

      long int h = s / q;

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

      if (t < 0)

        t += m;

      s = t;

    }

  for (i = N_SHUFFLE - 1; i >= 0; i--)

    {

      long int h = s / q;

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

      if (t < 0)

        t += m;

      s = t;

      state->shuffle[i] = s;

    }

  state->x = s;

  state->n = s;

  return;

}

static const gsl_rng_type ran1_type =

{"ran1",                        /* name */

 2147483646,                    /* RAND_MAX */

 1,                             /* RAND_MIN */

 sizeof (ran1_state_t),

 &ran1_set,

 &ran1_get,

 &ran1_get_double};

const gsl_rng_type *gsl_rng_ran1 = &ran1_type;