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 <string.h>
37#include "rand.h"
38#include "../hash.h"
39
40static inline int __seed(unsigned int x, unsigned int m)
41{
42	return (x < m) ? x + m : x;
43}
44
45static void __init_rand(struct frand_state *state, unsigned int seed)
46{
47	int cranks = 6;
48
49#define LCG(x, seed)  ((x) * 69069 ^ (seed))
50
51	state->s1 = __seed(LCG((2^31) + (2^17) + (2^7), seed), 1);
52	state->s2 = __seed(LCG(state->s1, seed), 7);
53	state->s3 = __seed(LCG(state->s2, seed), 15);
54
55	while (cranks--)
56		__rand(state);
57}
58
59void init_rand(struct frand_state *state)
60{
61	__init_rand(state, 1);
62}
63
64void init_rand_seed(struct frand_state *state, unsigned int seed)
65{
66	__init_rand(state, seed);
67}
68
69void __fill_random_buf(void *buf, unsigned int len, unsigned long seed)
70{
71	long *ptr = buf;
72
73	while ((void *) ptr - buf < len) {
74		*ptr = seed;
75		ptr++;
76		seed *= GOLDEN_RATIO_PRIME;
77		seed >>= 3;
78	}
79}
80
81unsigned long fill_random_buf(struct frand_state *fs, void *buf,
82			      unsigned int len)
83{
84	unsigned long r = __rand(fs);
85
86	if (sizeof(int) != sizeof(long *))
87		r *= (unsigned long) __rand(fs);
88
89	__fill_random_buf(buf, len, r);
90	return r;
91}
92
93unsigned long fill_random_buf_percentage(struct frand_state *fs, void *buf,
94					 unsigned int percentage,
95					 unsigned int segment, unsigned int len)
96{
97	unsigned long r = __rand(fs);
98	unsigned int this_len;
99
100	if (percentage == 100) {
101		memset(buf, 0, len);
102		return 0;
103	}
104
105	if (segment > len)
106		segment = len;
107
108	if (sizeof(int) != sizeof(long *))
109		r *= (unsigned long) __rand(fs);
110
111	while (len) {
112		/*
113		 * Fill random chunk
114		 */
115		this_len = (segment * (100 - percentage)) / 100;
116		if (this_len > len)
117			this_len = len;
118
119		__fill_random_buf(buf, this_len, r);
120
121		len -= this_len;
122		buf += this_len;
123
124		if (this_len > len)
125			this_len = len;
126
127		memset(buf, 0, this_len);
128		len -= this_len;
129		buf += this_len;
130	}
131
132	return r;
133}
134