rand.c revision 637ef8d9f7645135cf4829894d1e3983cd7a042e 
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
16   This is available on the net from L'Ecuyer's home page,
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
36#include "rand.h"
37#include "../hash.h"
38
39struct frand_state __fio_rand_state;
40
41static inline int __seed(unsigned int x, unsigned int m)
42{
43	return (x < m) ? x + m : x;
44}
45
46void init_rand(struct frand_state *state)
47{
48#define LCG(x)  ((x) * 69069)   /* super-duper LCG */
49
50	state->s1 = __seed(LCG((2^31) + (2^17) + (2^7)), 1);
51	state->s2 = __seed(LCG(state->s1), 7);
52	state->s3 = __seed(LCG(state->s2), 15);
53
54	__rand(state);
55	__rand(state);
56	__rand(state);
57	__rand(state);
58	__rand(state);
59	__rand(state);
60}
61
62void fill_random_buf(void *buf, unsigned int len)
63{
64	unsigned long r = __rand(&__fio_rand_state);
65	long *ptr = buf;
66
67	if (sizeof(int) != sizeof(*ptr))
68		r *= (unsigned long) __rand(&__fio_rand_state);
69
70	while ((void *) ptr - buf < len) {
71		*ptr = r;
72		ptr++;
73		r *= GOLDEN_RATIO_PRIME;
74		r >>= 3;
75	}
76}
77