/* rng/vax.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 the old vax generator MTH$RANDOM. The sequence is,

   x_{n+1} = (a x_n + c) mod m

   with a = 69069, c = 1 and m = 2^32. The seed specifies the initial

   value, x_1.

   The theoretical value of x_{10001} is 3051034865.

   The period of this generator is 2^32. */

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

static double vax_get_double (void *vstate);

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

typedef struct

  {

    unsigned long int x;

  }

vax_state_t;

static inline unsigned long int

vax_get (void *vstate)

{

  vax_state_t *state = (vax_state_t *) vstate;

  state->x = (69069 * state->x + 1) & 0xffffffffUL;

  return state->x;

}

static double

vax_get_double (void *vstate)

{

  return vax_get (vstate) / 4294967296.0 ;

}

static void

vax_set (void *vstate, unsigned long int s)

{

  vax_state_t *state = (vax_state_t *) vstate;

  /* default seed is 0. The constant term c stops the series from

     collapsing to 0,0,0,0,0,... */

  state->x = s;

  return;

}

static const gsl_rng_type vax_type =

{"vax",                         /* name */

 0xffffffffUL,                  /* RAND_MAX */

 0,                             /* RAND_MIN */

 sizeof (vax_state_t),

 &vax_set,

 &vax_get,

 &vax_get_double};

const gsl_rng_type *gsl_rng_vax = &vax_type;