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/* rng/ran0.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_errno.h>
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#include <gsl/gsl_rng.h>
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/* This is an implementation of the algorithm used in Numerical
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Recipe's ran0 generator. It is the same as MINSTD with an XOR mask
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of 123459876 on the seed.
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The period of this generator is 2^31.
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Note, if you choose a seed of 123459876 it would give a degenerate
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series 0,0,0,0, ... I've made that into an error. */
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static inline unsigned long int ran0_get (void *vstate);
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static double ran0_get_double (void *vstate);
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static void ran0_set (void *state, unsigned long int s);
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static const long int m = 2147483647, a = 16807, q = 127773, r = 2836;
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static const unsigned long int mask = 123459876;
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typedef struct
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{
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unsigned long int x;
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}
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ran0_state_t;
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static inline unsigned long int
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ran0_get (void *vstate)
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{
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ran0_state_t *state = (ran0_state_t *) vstate;
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const unsigned long int x = state->x;
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const long int h = x / q;
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const long int t = a * (x - h * q) - h * r;
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if (t < 0)
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{
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state->x = t + m;
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}
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else
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{
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state->x = t;
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}
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return state->x;
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}
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static double
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ran0_get_double (void *vstate)
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{
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return ran0_get (vstate) / 2147483647.0 ;
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}
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static void
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ran0_set (void *vstate, unsigned long int s)
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{
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ran0_state_t *state = (ran0_state_t *) vstate;
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if (s == mask)
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{
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GSL_ERROR_VOID ("ran0 should not use seed == mask",
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GSL_EINVAL);
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}
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state->x = s ^ mask;
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return;
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}
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static const gsl_rng_type ran0_type =
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{"ran0", /* name */
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2147483646, /* RAND_MAX */
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1, /* RAND_MIN */
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sizeof (ran0_state_t),
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&ran0_set,
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&ran0_get,
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&ran0_get_double};
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const gsl_rng_type *gsl_rng_ran0 = &ran0_type;
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