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/* rng/knuthran.c
*
* Copyright (C) 2001 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 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.
*/
/*
* 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 <config.h>
#include <stdlib.h>
#include <gsl/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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