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/* rng/randu.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 reincarnation of the infamously bad RANDU generator.
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The sequence is,
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x_{n+1} = (a x_n) mod m
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with a = 65539 and m = 2^31 = 2147483648. The seed specifies
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the initial value, x_1.
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The theoretical value of x_{10001} is 1623524161.
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The period of this generator is 2^29.
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Note: Knuth describes this generator as "really horrible".
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From: Park and Miller, "Random Number Generators: Good ones are
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hard to find" Communications of the ACM, October 1988, Volume 31,
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No 10, pages 1192-1201. */
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static inline unsigned long int randu_get (void *vstate);
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static double randu_get_double (void *vstate);
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static void randu_set (void *state, unsigned long int s);
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static const long int a = 65539;
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/* static const unsigned long int m = 2147483648UL; */
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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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randu_state_t;
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static inline unsigned long int
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randu_get (void *vstate)
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{
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randu_state_t *state = (randu_state_t *) vstate;
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/* The following line relies on unsigned 32-bit arithmetic */
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state->x = (a * state->x) & 0x7fffffffUL;
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return state->x;
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}
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static double
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randu_get_double (void *vstate)
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{
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return randu_get (vstate) / 2147483648.0 ;
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}
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static void
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randu_set (void *vstate, unsigned long int s)
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{
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randu_state_t *state = (randu_state_t *) vstate;
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if (s == 0)
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s = 1; /* default seed is 1 */
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state->x = s;
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return;
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}
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static const gsl_rng_type randu_type =
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{"randu", /* name */
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0x7fffffffUL, /* RAND_MAX */
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1, /* RAND_MIN */
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sizeof (randu_state_t),
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&randu_set,
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&randu_get,
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&randu_get_double};
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const gsl_rng_type *gsl_rng_randu = &randu_type;
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