/* rng/ran3.c

 * 

 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007, 2010 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 Knuths's

   subtractive generator, with the Numerical Recipe's ran3 paramters.

   It is a subtractive lagged fibonnaci generator. */

static inline unsigned long int ran3_get (void *vstate);

static double ran3_get_double (void *vstate);

static void ran3_set (void *state, unsigned long int s);

#define M_BIG 1000000000

#define M_SEED 161803398

typedef struct

  {

    unsigned int x;

    unsigned int y;

    unsigned long int buffer[56];

  }

ran3_state_t;

static inline unsigned long int

ran3_get (void *vstate)

{

  ran3_state_t *state = (ran3_state_t *) vstate;

  long int j;

  state->x++;

  if (state->x == 56)

    state->x = 1;

  state->y++;

  if (state->y == 56)

    state->y = 1;

  j = state->buffer[state->x] - state->buffer[state->y];

  if (j < 0)

    j += M_BIG;

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

  return j;

}

static double

ran3_get_double (void *vstate)

{

  return ran3_get (vstate) / (double) M_BIG ;

}

static void

ran3_set (void *vstate, unsigned long int s)

{

  ran3_state_t *state = (ran3_state_t *) vstate;

  int i, i1;

  long int j, k;

  if (s == 0)

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

  j = (M_SEED - s) % M_BIG;

  /* Avoid potential problem with negative values */

  if (j < 0) j += M_BIG;

  /* the zeroth element is never used, but we initialize it for

     consistency between states */

  state->buffer[0] = 0; 

  state->buffer[55] = j;

  k = 1;

  for (i = 1; i < 55; i++)

    {

      int n = (21 * i) % 55;

      state->buffer[n] = k;

      k = j - k;

      if (k < 0)

        k += M_BIG;

      j = state->buffer[n];

    }

  for (i1 = 0; i1 < 4; i1++)

    {

      for (i = 1; i < 56; i++)

        {

          long int t = state->buffer[i] - state->buffer[1 + (i + 30) % 55];

          if (t < 0)

            t += M_BIG;

          state->buffer[i] = t;

        }

    }

  state->x = 0;

  state->y = 31;

  return;

}

static const gsl_rng_type ran3_type =

{"ran3",                        /* name */

 M_BIG,                         /* RAND_MAX */

 0,                             /* RAND_MIN */

 sizeof (ran3_state_t),

 &ran3_set,

 &ran3_get,

 &ran3_get_double};

const gsl_rng_type *gsl_rng_ran3 = &ran3_type;