2 * Copyright (C) 2002 Atakan Gurkan
3 * Based on the file taus.c which has the notice
4 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 James Theiler, Brian Gough
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 3 of the License, or (at
9 * your option) any later version.
11 * This program is distributed in the hope that it will be useful, but
12 * WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
21 /* This is a maximally equidistributed combined, collision free
22 Tausworthe generator, with a period ~2^{113}. The sequence is,
24 x_n = (z1_n ^ z2_n ^ z3_n ^ z4_n)
26 b = (((z1_n << 6) ^ z1_n) >> 13)
27 z1_{n+1} = (((z1_n & 4294967294) << 18) ^ b)
28 b = (((z2_n << 2) ^ z2_n) >> 27)
29 z2_{n+1} = (((z2_n & 4294967288) << 2) ^ b)
30 b = (((z3_n << 13) ^ z3_n) >> 21)
31 z3_{n+1} = (((z3_n & 4294967280) << 7) ^ b)
32 b = (((z4_n << 3) ^ z4_n) >> 12)
33 z4_{n+1} = (((z4_n & 4294967168) << 13) ^ b)
35 computed modulo 2^32. In the formulas above '^' means exclusive-or
36 (C-notation), not exponentiation.
37 The algorithm is for 32-bit integers, hence a bitmask is used to clear
38 all but least significant 32 bits, after left shifts, to make the code
39 work on architectures where integers are 64-bit.
41 The generator is initialized with
42 zi = (69069 * z{i+1}) MOD 2^32 where z0 is the seed provided
43 During initialization a check is done to make sure that the initial seeds
44 have a required number of their most significant bits set.
45 After this, the state is passed through the RNG 10 times to ensure the
46 state satisfies a recurrence relation.
49 P. L'Ecuyer, "Tables of Maximally-Equidistributed Combined LFSR Generators",
50 Mathematics of Computation, 68, 225 (1999), 261--269.
51 http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
52 P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe Generators",
53 Mathematics of Computation, 65, 213 (1996), 203--213.
54 http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
55 the online version of the latter contains corrections to the print version.
60 #include <gsl/gsl_rng.h>
62 #define LCG(n) ((69069UL * n) & 0xffffffffUL)
63 #define MASK 0xffffffffUL
65 static inline unsigned long int taus113_get (void *vstate);
66 static double taus113_get_double (void *vstate);
67 static void taus113_set (void *state, unsigned long int s);
71 unsigned long int z1, z2, z3, z4;
75 static inline unsigned long
76 taus113_get (void *vstate)
78 taus113_state_t *state = (taus113_state_t *) vstate;
79 unsigned long b1, b2, b3, b4;
81 b1 = ((((state->z1 << 6UL) & MASK) ^ state->z1) >> 13UL);
82 state->z1 = ((((state->z1 & 4294967294UL) << 18UL) & MASK) ^ b1);
84 b2 = ((((state->z2 << 2UL) & MASK) ^ state->z2) >> 27UL);
85 state->z2 = ((((state->z2 & 4294967288UL) << 2UL) & MASK) ^ b2);
87 b3 = ((((state->z3 << 13UL) & MASK) ^ state->z3) >> 21UL);
88 state->z3 = ((((state->z3 & 4294967280UL) << 7UL) & MASK) ^ b3);
90 b4 = ((((state->z4 << 3UL) & MASK) ^ state->z4) >> 12UL);
91 state->z4 = ((((state->z4 & 4294967168UL) << 13UL) & MASK) ^ b4);
93 return (state->z1 ^ state->z2 ^ state->z3 ^ state->z4);
98 taus113_get_double (void *vstate)
100 return taus113_get (vstate) / 4294967296.0;
104 taus113_set (void *vstate, unsigned long int s)
106 taus113_state_t *state = (taus113_state_t *) vstate;
109 s = 1UL; /* default seed is 1 */
114 state->z2 = LCG (state->z1);
117 state->z3 = LCG (state->z2);
118 if (state->z3 < 16UL)
120 state->z4 = LCG (state->z3);
121 if (state->z4 < 128UL)
124 /* Calling RNG ten times to satify recurrence condition */
139 static const gsl_rng_type taus113_type = {
140 "taus113", /* name */
141 0xffffffffUL, /* RAND_MAX */
143 sizeof (taus113_state_t),
149 const gsl_rng_type *gsl_rng_taus113 = &taus113_type;
152 /* Rules for analytic calculations using GNU Emacs Calc:
153 (used to find the values for the test program)
155 [ LCG(n) := n * 69069 mod (2^32) ]
157 [ b1(x) := rsh(xor(lsh(x, 6), x), 13),
158 q1(x) := xor(lsh(and(x, 4294967294), 18), b1(x)),
159 b2(x) := rsh(xor(lsh(x, 2), x), 27),
160 q2(x) := xor(lsh(and(x, 4294967288), 2), b2(x)),
161 b3(x) := rsh(xor(lsh(x, 13), x), 21),
162 q3(x) := xor(lsh(and(x, 4294967280), 7), b3(x)),
163 b4(x) := rsh(xor(lsh(x, 3), x), 12),
164 q4(x) := xor(lsh(and(x, 4294967168), 13), b4(x))
167 [ S([z1,z2,z3,z4]) := [q1(z1), q2(z2), q3(z3), q4(z4)] ]