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 } 134
