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 <linux/types.h> 37 #include <linux/percpu.h> 38 #include <linux/export.h> 39 #include <linux/jiffies.h> 40 #include <linux/random.h> 41 42 static DEFINE_PER_CPU(struct rnd_state, net_rand_state); 43 44 /** 45 * prandom32 - seeded pseudo-random number generator. 46 * @state: pointer to state structure holding seeded state. 47 * 48 * This is used for pseudo-randomness with no outside seeding. 49 * For more random results, use random32(). 50 */ 51 u32 prandom32(struct rnd_state *state) 52 { 53 #define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b) 54 55 state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12); 56 state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4); 57 state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17); 58 59 return (state->s1 ^ state->s2 ^ state->s3); 60 } 61 EXPORT_SYMBOL(prandom32); 62 63 /** 64 * random32 - pseudo random number generator 65 * 66 * A 32 bit pseudo-random number is generated using a fast 67 * algorithm suitable for simulation. This algorithm is NOT 68 * considered safe for cryptographic use. 69 */ 70 u32 random32(void) 71 { 72 unsigned long r; 73 struct rnd_state *state = &get_cpu_var(net_rand_state); 74 r = prandom32(state); 75 put_cpu_var(state); 76 return r; 77 } 78 EXPORT_SYMBOL(random32); 79 80 /** 81 * srandom32 - add entropy to pseudo random number generator 82 * @seed: seed value 83 * 84 * Add some additional seeding to the random32() pool. 85 */ 86 void srandom32(u32 entropy) 87 { 88 int i; 89 /* 90 * No locking on the CPUs, but then somewhat random results are, well, 91 * expected. 92 */ 93 for_each_possible_cpu (i) { 94 struct rnd_state *state = &per_cpu(net_rand_state, i); 95 state->s1 = __seed(state->s1 ^ entropy, 1); 96 } 97 } 98 EXPORT_SYMBOL(srandom32); 99 100 /* 101 * Generate some initially weak seeding values to allow 102 * to start the random32() engine. 103 */ 104 static int __init random32_init(void) 105 { 106 int i; 107 108 for_each_possible_cpu(i) { 109 struct rnd_state *state = &per_cpu(net_rand_state,i); 110 111 #define LCG(x) ((x) * 69069) /* super-duper LCG */ 112 state->s1 = __seed(LCG(i + jiffies), 1); 113 state->s2 = __seed(LCG(state->s1), 7); 114 state->s3 = __seed(LCG(state->s2), 15); 115 116 /* "warm it up" */ 117 prandom32(state); 118 prandom32(state); 119 prandom32(state); 120 prandom32(state); 121 prandom32(state); 122 prandom32(state); 123 } 124 return 0; 125 } 126 core_initcall(random32_init); 127 128 /* 129 * Generate better values after random number generator 130 * is fully initialized. 131 */ 132 static int __init random32_reseed(void) 133 { 134 int i; 135 136 for_each_possible_cpu(i) { 137 struct rnd_state *state = &per_cpu(net_rand_state,i); 138 u32 seeds[3]; 139 140 get_random_bytes(&seeds, sizeof(seeds)); 141 state->s1 = __seed(seeds[0], 1); 142 state->s2 = __seed(seeds[1], 7); 143 state->s3 = __seed(seeds[2], 15); 144 145 /* mix it in */ 146 prandom32(state); 147 } 148 return 0; 149 } 150 late_initcall(random32_reseed); 151