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/* rng/ranlux.c
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*
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* Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 James Theiler, Brian Gough
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or (at
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* your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#include <config.h>
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#include <stdlib.h>
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#include <gsl/gsl_rng.h>
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/* This is a lagged fibonacci generator with skipping developed by Luescher.
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The sequence is a series of 24-bit integers, x_n,
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x_n = d_n + b_n
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where d_n = x_{n-10} - x_{n-24} - c_{n-1}, b_n = 0 if d_n >= 0 and
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b_n = 2^24 if d_n < 0, c_n = 0 if d_n >= 0 and c_n = 1 if d_n < 0,
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where after 24 samples a group of p integers are "skipped", to
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reduce correlations. By default p = 199, but can be increased to
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365.
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The period of the generator is around 10^171.
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From: M. Luescher, "A portable high-quality random number generator
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for lattice field theory calculations", Computer Physics
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Communications, 79 (1994) 100-110.
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Available on the net as hep-lat/9309020 at http://xxx.lanl.gov/
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See also,
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F. James, "RANLUX: A Fortran implementation of the high-quality
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pseudo-random number generator of Luscher", Computer Physics
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Communications, 79 (1994) 111-114
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Kenneth G. Hamilton, F. James, "Acceleration of RANLUX", Computer
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Physics Communications, 101 (1997) 241-248
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Kenneth G. Hamilton, "Assembler RANLUX for PCs", Computer Physics
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Communications, 101 (1997) 249-253 */
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static inline unsigned long int ranlux_get (void *vstate);
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static double ranlux_get_double (void *vstate);
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static void ranlux_set_lux (void *state, unsigned long int s, unsigned int luxury);
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static void ranlux_set (void *state, unsigned long int s);
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static void ranlux389_set (void *state, unsigned long int s);
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static const unsigned long int mask_lo = 0x00ffffffUL; /* 2^24 - 1 */
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static const unsigned long int mask_hi = ~0x00ffffffUL;
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static const unsigned long int two24 = 16777216; /* 2^24 */
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typedef struct
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{
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unsigned int i;
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unsigned int j;
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unsigned int n;
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unsigned int skip;
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unsigned int carry;
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unsigned long int u[24];
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}
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ranlux_state_t;
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static inline unsigned long int increment_state (ranlux_state_t * state);
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static inline unsigned long int
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increment_state (ranlux_state_t * state)
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{
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unsigned int i = state->i;
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unsigned int j = state->j;
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long int delta = state->u[j] - state->u[i] - state->carry;
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if (delta & mask_hi)
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{
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state->carry = 1;
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delta &= mask_lo;
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}
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else
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{
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state->carry = 0;
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}
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state->u[i] = delta;
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if (i == 0)
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{
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i = 23;
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}
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else
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{
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i--;
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}
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state->i = i;
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if (j == 0)
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{
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j = 23;
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}
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else
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{
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j--;
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}
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state->j = j;
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return delta;
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}
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static inline unsigned long int
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ranlux_get (void *vstate)
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{
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ranlux_state_t *state = (ranlux_state_t *) vstate;
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const unsigned int skip = state->skip;
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unsigned long int r = increment_state (state);
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state->n++;
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if (state->n == 24)
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{
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unsigned int i;
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state->n = 0;
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for (i = 0; i < skip; i++)
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increment_state (state);
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}
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return r;
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}
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static double
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ranlux_get_double (void *vstate)
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{
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return ranlux_get (vstate) / 16777216.0;
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}
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static void
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ranlux_set_lux (void *vstate, unsigned long int s, unsigned int luxury)
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{
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ranlux_state_t *state = (ranlux_state_t *) vstate;
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int i;
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long int seed;
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if (s == 0)
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s = 314159265; /* default seed is 314159265 */
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seed = s;
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/* This is the initialization algorithm of F. James, widely in use
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for RANLUX. */
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for (i = 0; i < 24; i++)
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{
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unsigned long int k = seed / 53668;
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seed = 40014 * (seed - k * 53668) - k * 12211;
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if (seed < 0)
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{
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seed += 2147483563;
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}
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state->u[i] = seed % two24;
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}
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state->i = 23;
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state->j = 9;
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state->n = 0;
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state->skip = luxury - 24;
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if (state->u[23] & mask_hi)
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{
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state->carry = 1;
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}
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else
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{
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state->carry = 0;
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}
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}
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static void
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ranlux_set (void *vstate, unsigned long int s)
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{
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ranlux_set_lux (vstate, s, 223);
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}
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static void
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ranlux389_set (void *vstate, unsigned long int s)
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{
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ranlux_set_lux (vstate, s, 389);
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}
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static const gsl_rng_type ranlux_type =
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{"ranlux", /* name */
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0x00ffffffUL, /* RAND_MAX */
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0, /* RAND_MIN */
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sizeof (ranlux_state_t),
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&ranlux_set,
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&ranlux_get,
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&ranlux_get_double};
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static const gsl_rng_type ranlux389_type =
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{"ranlux389", /* name */
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0x00ffffffUL, /* RAND_MAX */
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0, /* RAND_MIN */
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sizeof (ranlux_state_t),
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&ranlux389_set,
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&ranlux_get,
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&ranlux_get_double};
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const gsl_rng_type *gsl_rng_ranlux = &ranlux_type;
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const gsl_rng_type *gsl_rng_ranlux389 = &ranlux389_type;
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