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- /* rng/ran0.c
- *
- * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 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 3 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 "gsl__config.h"
- #include <stdlib.h>
- #include "gsl_errno.h"
- #include "gsl_rng.h"
- /* This is an implementation of the algorithm used in Numerical
- Recipe's ran0 generator. It is the same as MINSTD with an XOR mask
- of 123459876 on the seed.
- The period of this generator is 2^31.
- Note, if you choose a seed of 123459876 it would give a degenerate
- series 0,0,0,0, ... I've made that into an error. */
- static inline unsigned long int ran0_get (void *vstate);
- static double ran0_get_double (void *vstate);
- static void ran0_set (void *state, unsigned long int s);
- static const long int m = 2147483647, a = 16807, q = 127773, r = 2836;
- static const unsigned long int mask = 123459876;
- typedef struct
- {
- unsigned long int x;
- }
- ran0_state_t;
- static inline unsigned long int
- ran0_get (void *vstate)
- {
- ran0_state_t *state = (ran0_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;
- }
- return state->x;
- }
- static double
- ran0_get_double (void *vstate)
- {
- return ran0_get (vstate) / 2147483647.0 ;
- }
- static void
- ran0_set (void *vstate, unsigned long int s)
- {
- ran0_state_t *state = (ran0_state_t *) vstate;
- if (s == mask)
- {
- GSL_ERROR_VOID ("ran0 should not use seed == mask",
- GSL_EINVAL);
- }
- state->x = s ^ mask;
- return;
- }
- static const gsl_rng_type ran0_type =
- {"ran0", /* name */
- 2147483646, /* RAND_MAX */
- 1, /* RAND_MIN */
- sizeof (ran0_state_t),
- &ran0_set,
- &ran0_get,
- &ran0_get_double};
- const gsl_rng_type *gsl_rng_ran0 = &ran0_type;
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