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

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