CommitLineData
79c94bd3
JA
1/*
2 This is a maximally equidistributed combined Tausworthe generator
3 based on code from GNU Scientific Library 1.5 (30 Jun 2004)
4
5 x_n = (s1_n ^ s2_n ^ s3_n)
6
7 s1_{n+1} = (((s1_n & 4294967294) <<12) ^ (((s1_n <<13) ^ s1_n) >>19))
8 s2_{n+1} = (((s2_n & 4294967288) << 4) ^ (((s2_n << 2) ^ s2_n) >>25))
9 s3_{n+1} = (((s3_n & 4294967280) <<17) ^ (((s3_n << 3) ^ s3_n) >>11))
10
11 The period of this generator is about 2^88.
12
13 From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
14 Generators", Mathematics of Computation, 65, 213 (1996), 203--213.
15
17
18 http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
19 ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
20
21 There is an erratum in the paper "Tables of Maximally
22 Equidistributed Combined LFSR Generators", Mathematics of
23 Computation, 68, 225 (1999), 261--269:
24 http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
25
26 ... the k_j most significant bits of z_j must be non-
27 zero, for each j. (Note: this restriction also applies to the
28 computer code given in [4], but was mistakenly not mentioned in
29 that paper.)
30
31 This affects the seeding procedure by imposing the requirement
32 s1 > 1, s2 > 7, s3 > 15.
33
34*/
35
1fbbf72e
JA
36#include "rand.h"
37
38struct frand_state __fio_rand_state;
39
40static inline int __seed(unsigned int x, unsigned int m)
41{
42 return (x < m) ? x + m : x;
43}
44
45void init_rand(struct frand_state *state)
46{
47#define LCG(x) ((x) * 69069) /* super-duper LCG */
48
49 state->s1 = __seed(LCG((2^31) + (2^17) + (2^7)), 1);
50 state->s2 = __seed(LCG(state->s1), 7);
51 state->s3 = __seed(LCG(state->s2), 15);
52
53 __rand(state);
54 __rand(state);
55 __rand(state);
56 __rand(state);
57 __rand(state);
58 __rand(state);
59}