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- /* rng/knuthran.c
- *
- * Copyright (C) 2001, 2007 Brian Gough, Carlo Perassi
- *
- * 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.
- */
- /*
- * This generator is taken from
- *
- * Donald E. Knuth
- * The Art of Computer Programming
- * Volume 2
- * Third Edition
- * Addison-Wesley
- * Section 3.6
- *
- * The comments are taken from the book
- * Our comments are signed
- */
- #include "gsl__config.h"
- #include <stdlib.h>
- #include "gsl_rng.h"
- #define BUFLEN 2009 /* [Brian]: length of the buffer aa[] */
- #define KK 100 /* the long lag */
- #define LL 37 /* the short lag */
- #define MM (1L << 30) /* the modulus */
- #define TT 70 /* guaranteed separation between streams */
- #define evenize(x) ((x) & (MM - 2)) /* make x even */
- #define is_odd(x) ((x) & 1) /* the units bit of x */
- #define mod_diff(x, y) (((x) - (y)) & (MM - 1)) /* (x - y) mod MM */
- static inline void ran_array (unsigned long int aa[], unsigned int n,
- unsigned long int ran_x[]);
- static inline unsigned long int ran_get (void *vstate);
- static double ran_get_double (void *vstate);
- static void ran_set (void *state, unsigned long int s);
- typedef struct
- {
- unsigned int i;
- unsigned long int aa[BUFLEN]; /* [Carlo]: I can't pass n to ran_array like
- Knuth does */
- unsigned long int ran_x[KK]; /* the generator state */
- }
- ran_state_t;
- static inline void
- ran_array (unsigned long int aa[], unsigned int n, unsigned long int ran_x[])
- {
- unsigned int i;
- unsigned int j;
- for (j = 0; j < KK; j++)
- aa[j] = ran_x[j];
- for (; j < n; j++)
- aa[j] = mod_diff (aa[j - KK], aa[j - LL]);
- for (i = 0; i < LL; i++, j++)
- ran_x[i] = mod_diff (aa[j - KK], aa[j - LL]);
- for (; i < KK; i++, j++)
- ran_x[i] = mod_diff (aa[j - KK], ran_x[i - LL]);
- }
- static inline unsigned long int
- ran_get (void *vstate)
- {
- ran_state_t *state = (ran_state_t *) vstate;
- unsigned int i = state->i;
- if (i == 0)
- {
- /* fill buffer with new random numbers */
- ran_array (state->aa, BUFLEN, state->ran_x);
- }
- state->i = (i + 1) % BUFLEN;
- return state->aa[i];
- }
- static double
- ran_get_double (void *vstate)
- {
- ran_state_t *state = (ran_state_t *) vstate;
- return ran_get (state) / 1073741824.0; /* [Carlo]: RAND_MAX + 1 */
- }
- static void
- ran_set (void *vstate, unsigned long int s)
- {
- ran_state_t *state = (ran_state_t *) vstate;
- long x[KK + KK - 1]; /* the preparation buffer */
- register int j;
- register int t;
- register long ss = evenize (s + 2);
- for (j = 0; j < KK; j++)
- {
- x[j] = ss; /* bootstrap the buffer */
- ss <<= 1;
- if (ss >= MM) /* cyclic shift 29 bits */
- ss -= MM - 2;
- }
- for (; j < KK + KK - 1; j++)
- x[j] = 0;
- x[1]++; /* make x[1] (and only x[1]) odd */
- ss = s & (MM - 1);
- t = TT - 1;
- while (t)
- {
- for (j = KK - 1; j > 0; j--) /* square */
- x[j + j] = x[j];
- for (j = KK + KK - 2; j > KK - LL; j -= 2)
- x[KK + KK - 1 - j] = evenize (x[j]);
- for (j = KK + KK - 2; j >= KK; j--)
- if (is_odd (x[j]))
- {
- x[j - (KK - LL)] = mod_diff (x[j - (KK - LL)], x[j]);
- x[j - KK] = mod_diff (x[j - KK], x[j]);
- }
- if (is_odd (ss))
- { /* multiply by "z" */
- for (j = KK; j > 0; j--)
- x[j] = x[j - 1];
- x[0] = x[KK]; /* shift the buffer cyclically */
- if (is_odd (x[KK]))
- x[LL] = mod_diff (x[LL], x[KK]);
- }
- if (ss)
- ss >>= 1;
- else
- t--;
- }
- state->i = 0;
- for (j = 0; j < LL; j++)
- state->ran_x[j + KK - LL] = x[j];
- for (; j < KK; j++)
- state->ran_x[j - LL] = x[j];
- return;
- }
- static const gsl_rng_type ran_type = {
- "knuthran", /* name */
- 0x3fffffffUL, /* RAND_MAX *//* [Carlo]: (2 ^ 30) - 1 */
- 0, /* RAND_MIN */
- sizeof (ran_state_t),
- &ran_set,
- &ran_get,
- &ran_get_double
- };
- const gsl_rng_type *gsl_rng_knuthran = &ran_type;
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