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- /* rng/rand48.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 <math.h>
- #include <stdlib.h>
- #include "gsl_sys.h"
- #include "gsl_rng.h"
- /* This is the Unix rand48() generator. The generator returns the
- upper 32 bits from each term of the sequence,
- x_{n+1} = (a x_n + c) mod m
- using 48-bit unsigned arithmetic, with a = 0x5DEECE66D , c = 0xB
- and m = 2^48. The seed specifies the upper 32 bits of the initial
- value, x_1, with the lower 16 bits set to 0x330E.
- The theoretical value of x_{10001} is 244131582646046.
- The period of this generator is ? FIXME (probably around 2^48). */
- static inline void rand48_advance (void *vstate);
- static unsigned long int rand48_get (void *vstate);
- static double rand48_get_double (void *vstate);
- static void rand48_set (void *state, unsigned long int s);
- static const unsigned short int a0 = 0xE66D ;
- static const unsigned short int a1 = 0xDEEC ;
- static const unsigned short int a2 = 0x0005 ;
- static const unsigned short int c0 = 0x000B ;
- typedef struct
- {
- unsigned short int x0, x1, x2;
- }
- rand48_state_t;
- static inline void
- rand48_advance (void *vstate)
- {
- rand48_state_t *state = (rand48_state_t *) vstate;
- /* work with unsigned long ints throughout to get correct integer
- promotions of any unsigned short ints */
- const unsigned long int x0 = (unsigned long int) state->x0 ;
- const unsigned long int x1 = (unsigned long int) state->x1 ;
- const unsigned long int x2 = (unsigned long int) state->x2 ;
- unsigned long int a ;
-
- a = a0 * x0 + c0 ;
- state->x0 = (a & 0xFFFF) ;
-
- a >>= 16 ;
- /* although the next line may overflow we only need the top 16 bits
- in the following stage, so it does not matter */
- a += a0 * x1 + a1 * x0 ;
- state->x1 = (a & 0xFFFF) ;
- a >>= 16 ;
- a += a0 * x2 + a1 * x1 + a2 * x0 ;
- state->x2 = (a & 0xFFFF) ;
- }
- static unsigned long int
- rand48_get (void *vstate)
- {
- unsigned long int x1, x2;
- rand48_state_t *state = (rand48_state_t *) vstate;
- rand48_advance (state) ;
- x2 = (unsigned long int) state->x2;
- x1 = (unsigned long int) state->x1;
- return (x2 << 16) + x1;
- }
- static double
- rand48_get_double (void * vstate)
- {
- rand48_state_t *state = (rand48_state_t *) vstate;
- rand48_advance (state) ;
- return (ldexp((double) state->x2, -16)
- + ldexp((double) state->x1, -32)
- + ldexp((double) state->x0, -48)) ;
- }
- static void
- rand48_set (void *vstate, unsigned long int s)
- {
- rand48_state_t *state = (rand48_state_t *) vstate;
- if (s == 0) /* default seed */
- {
- state->x0 = 0x330E ;
- state->x1 = 0xABCD ;
- state->x2 = 0x1234 ;
- }
- else
- {
- state->x0 = 0x330E ;
- state->x1 = s & 0xFFFF ;
- state->x2 = (s >> 16) & 0xFFFF ;
- }
- return;
- }
- static const gsl_rng_type rand48_type =
- {"rand48", /* name */
- 0xffffffffUL, /* RAND_MAX */
- 0, /* RAND_MIN */
- sizeof (rand48_state_t),
- &rand48_set,
- &rand48_get,
- &rand48_get_double
- };
- const gsl_rng_type *gsl_rng_rand48 = &rand48_type;
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