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/* 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;
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