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/* rng/ran1.c
*
* Copyright (C) 1996, 1997, 1998, 1999, 2000 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 2 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;
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