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/module.h> 39 #include <linux/jiffies.h> 40 #include <linux/random.h> 41 42 struct rnd_state { 43 u32 s1, s2, s3; 44 }; 45 46 static DEFINE_PER_CPU(struct rnd_state, net_rand_state); 47 48 static u32 __random32(struct rnd_state *state) 49 { 50 #define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b) 51 52 state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12); 53 state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4); 54 state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17); 55 56 return (state->s1 ^ state->s2 ^ state->s3); 57 } 58 59 static void __set_random32(struct rnd_state *state, unsigned long s) 60 { 61 if (s == 0) 62 s = 1; /* default seed is 1 */ 63 64 #define LCG(n) (69069 * n) 65 state->s1 = LCG(s); 66 state->s2 = LCG(state->s1); 67 state->s3 = LCG(state->s2); 68 69 /* "warm it up" */ 70 __random32(state); 71 __random32(state); 72 __random32(state); 73 __random32(state); 74 __random32(state); 75 __random32(state); 76 } 77 78 /** 79 * random32 - pseudo random number generator 80 * 81 * A 32 bit pseudo-random number is generated using a fast 82 * algorithm suitable for simulation. This algorithm is NOT 83 * considered safe for cryptographic use. 84 */ 85 u32 random32(void) 86 { 87 unsigned long r; 88 struct rnd_state *state = &get_cpu_var(net_rand_state); 89 r = __random32(state); 90 put_cpu_var(state); 91 return r; 92 } 93 EXPORT_SYMBOL(random32); 94 95 /** 96 * srandom32 - add entropy to pseudo random number generator 97 * @seed: seed value 98 * 99 * Add some additional seeding to the random32() pool. 100 */ 101 void srandom32(u32 entropy) 102 { 103 int i; 104 /* 105 * No locking on the CPUs, but then somewhat random results are, well, 106 * expected. 107 */ 108 for_each_possible_cpu (i) { 109 struct rnd_state *state = &per_cpu(net_rand_state, i); 110 __set_random32(state, state->s1 ^ entropy); 111 } 112 } 113 EXPORT_SYMBOL(srandom32); 114 115 /* 116 * Generate some initially weak seeding values to allow 117 * to start the random32() engine. 118 */ 119 static int __init random32_init(void) 120 { 121 int i; 122 123 for_each_possible_cpu(i) { 124 struct rnd_state *state = &per_cpu(net_rand_state,i); 125 __set_random32(state, i + jiffies); 126 } 127 return 0; 128 } 129 core_initcall(random32_init); 130 131 /* 132 * Generate better values after random number generator 133 * is fully initalized. 134 */ 135 static int __init random32_reseed(void) 136 { 137 int i; 138 unsigned long seed; 139 140 for_each_possible_cpu(i) { 141 struct rnd_state *state = &per_cpu(net_rand_state,i); 142 143 get_random_bytes(&seed, sizeof(seed)); 144 __set_random32(state, seed); 145 } 146 return 0; 147 } 148 late_initcall(random32_reseed); 149