/* rng/rand.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 BSD rand() generator. The sequence is

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

   with a = 1103515245, c = 12345 and m = 2^31 = 2147483648. The seed

   specifies the initial value, x_1.

   The theoretical value of x_{10001} is 1910041713.

   The period of this generator is 2^31.

   The rand() generator is not very good -- the low bits of successive

   numbers are correlated. */

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

static double rand_get_double (void *vstate);

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

typedef struct

  {

    unsigned long int x;

  }

rand_state_t;

static inline unsigned long int

rand_get (void *vstate)

{

  rand_state_t *state = (rand_state_t *) vstate;

  /* The following line relies on unsigned 32-bit arithmetic */

  state->x = (1103515245 * state->x + 12345) & 0x7fffffffUL;

  return state->x;

}

static double

rand_get_double (void *vstate)

{

  return rand_get (vstate) / 2147483648.0 ;

}

static void

rand_set (void *vstate, unsigned long int s)

{

  rand_state_t *state = (rand_state_t *) vstate;

  state->x = s;

  return;

}

static const gsl_rng_type rand_type =

{"rand",                        /* name */

 0x7fffffffUL,                  /* RAND_MAX */

 0,                             /* RAND_MIN */

 sizeof (rand_state_t),

 &rand_set,

 &rand_get,

 &rand_get_double};

const gsl_rng_type *gsl_rng_rand = &rand_type;