| /* 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; |