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/* rng/ranlux.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 a lagged fibonacci generator with skipping developed by Luescher.
The sequence is a series of 24-bit integers, x_n,
x_n = d_n + b_n
where d_n = x_{n-10} - x_{n-24} - c_{n-1}, b_n = 0 if d_n >= 0 and
b_n = 2^24 if d_n < 0, c_n = 0 if d_n >= 0 and c_n = 1 if d_n < 0,
where after 24 samples a group of p integers are "skipped", to
reduce correlations. By default p = 199, but can be increased to
365.
The period of the generator is around 10^171.
From: M. Luescher, "A portable high-quality random number generator
for lattice field theory calculations", Computer Physics
Communications, 79 (1994) 100-110.
Available on the net as hep-lat/9309020 at http://xxx.lanl.gov/
See also,
F. James, "RANLUX: A Fortran implementation of the high-quality
pseudo-random number generator of Luscher", Computer Physics
Communications, 79 (1994) 111-114
Kenneth G. Hamilton, F. James, "Acceleration of RANLUX", Computer
Physics Communications, 101 (1997) 241-248
Kenneth G. Hamilton, "Assembler RANLUX for PCs", Computer Physics
Communications, 101 (1997) 249-253 */
static inline unsigned long int ranlux_get (void *vstate);
static double ranlux_get_double (void *vstate);
static void ranlux_set_lux (void *state, unsigned long int s, unsigned int luxury);
static void ranlux_set (void *state, unsigned long int s);
static void ranlux389_set (void *state, unsigned long int s);
static const unsigned long int mask_lo = 0x00ffffffUL; /* 2^24 - 1 */
static const unsigned long int mask_hi = ~0x00ffffffUL;
static const unsigned long int two24 = 16777216; /* 2^24 */
typedef struct
{
unsigned int i;
unsigned int j;
unsigned int n;
unsigned int skip;
unsigned int carry;
unsigned long int u[24];
}
ranlux_state_t;
static inline unsigned long int increment_state (ranlux_state_t * state);
static inline unsigned long int
increment_state (ranlux_state_t * state)
{
unsigned int i = state->i;
unsigned int j = state->j;
long int delta = state->u[j] - state->u[i] - state->carry;
if (delta & mask_hi)
{
state->carry = 1;
delta &= mask_lo;
}
else
{
state->carry = 0;
}
state->u[i] = delta;
if (i == 0)
{
i = 23;
}
else
{
i--;
}
state->i = i;
if (j == 0)
{
j = 23;
}
else
{
j--;
}
state->j = j;
return delta;
}
static inline unsigned long int
ranlux_get (void *vstate)
{
ranlux_state_t *state = (ranlux_state_t *) vstate;
const unsigned int skip = state->skip;
unsigned long int r = increment_state (state);
state->n++;
if (state->n == 24)
{
unsigned int i;
state->n = 0;
for (i = 0; i < skip; i++)
increment_state (state);
}
return r;
}
static double
ranlux_get_double (void *vstate)
{
return ranlux_get (vstate) / 16777216.0;
}
static void
ranlux_set_lux (void *vstate, unsigned long int s, unsigned int luxury)
{
ranlux_state_t *state = (ranlux_state_t *) vstate;
int i;
long int seed;
if (s == 0)
s = 314159265; /* default seed is 314159265 */
seed = s;
/* This is the initialization algorithm of F. James, widely in use
for RANLUX. */
for (i = 0; i < 24; i++)
{
unsigned long int k = seed / 53668;
seed = 40014 * (seed - k * 53668) - k * 12211;
if (seed < 0)
{
seed += 2147483563;
}
state->u[i] = seed % two24;
}
state->i = 23;
state->j = 9;
state->n = 0;
state->skip = luxury - 24;
if (state->u[23] & mask_hi)
{
state->carry = 1;
}
else
{
state->carry = 0;
}
}
static void
ranlux_set (void *vstate, unsigned long int s)
{
ranlux_set_lux (vstate, s, 223);
}
static void
ranlux389_set (void *vstate, unsigned long int s)
{
ranlux_set_lux (vstate, s, 389);
}
static const gsl_rng_type ranlux_type =
{"ranlux", /* name */
0x00ffffffUL, /* RAND_MAX */
0, /* RAND_MIN */
sizeof (ranlux_state_t),
&ranlux_set,
&ranlux_get,
&ranlux_get_double};
static const gsl_rng_type ranlux389_type =
{"ranlux389", /* name */
0x00ffffffUL, /* RAND_MAX */
0, /* RAND_MIN */
sizeof (ranlux_state_t),
&ranlux389_set,
&ranlux_get,
&ranlux_get_double};
const gsl_rng_type *gsl_rng_ranlux = &ranlux_type;
const gsl_rng_type *gsl_rng_ranlux389 = &ranlux389_type;
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