| 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 | |
| 40 | static inline int __seed(unsigned int x, unsigned int m) |
| 41 | { |
| 42 | return (x < m) ? x + m : x; |
| 43 | } |
| 44 | |
| 45 | static 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 | |
| 59 | void init_rand(struct frand_state *state) |
| 60 | { |
| 61 | __init_rand(state, 1); |
| 62 | } |
| 63 | |
| 64 | void init_rand_seed(struct frand_state *state, unsigned int seed) |
| 65 | { |
| 66 | __init_rand(state, seed); |
| 67 | } |
| 68 | |
| 69 | void __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 | |
| 81 | unsigned 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 | |
| 93 | unsigned 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 | } |