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79c94bd3
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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 36#include "rand.h"
637ef8d9 37#include "../hash.h"
1fbbf72e 38
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39static inline int __seed(unsigned int x, unsigned int m)
40{
41 return (x < m) ? x + m : x;
42}
43
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44static void __init_rand(struct frand_state *state, unsigned int seed)
45{
46 int cranks = 6;
47
48#define LCG(x, seed) ((x) * 69069 ^ (seed))
49
50 state->s1 = __seed(LCG((2^31) + (2^17) + (2^7), seed), 1);
51 state->s2 = __seed(LCG(state->s1, seed), 7);
52 state->s3 = __seed(LCG(state->s2, seed), 15);
53
54 while (cranks--)
55 __rand(state);
56}
57
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58void init_rand(struct frand_state *state)
59{
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60 __init_rand(state, 1);
61}
62
63void init_rand_seed(struct frand_state *state, unsigned int seed)
64{
65 __init_rand(state, seed);
1fbbf72e 66}
637ef8d9 67
7d9fb455 68void __fill_random_buf(void *buf, unsigned int len, unsigned long seed)
637ef8d9 69{
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70 long *ptr = buf;
71
637ef8d9 72 while ((void *) ptr - buf < len) {
7d9fb455 73 *ptr = seed;
637ef8d9 74 ptr++;
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75 seed *= GOLDEN_RATIO_PRIME;
76 seed >>= 3;
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77 }
78}
7d9fb455 79
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80unsigned long fill_random_buf(struct frand_state *fs, void *buf,
81 unsigned int len)
7d9fb455 82{
3545a109 83 unsigned long r = __rand(fs);
7d9fb455
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84
85 if (sizeof(int) != sizeof(long *))
3545a109 86 r *= (unsigned long) __rand(fs);
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87
88 __fill_random_buf(buf, len, r);
89 return r;
90}