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 * prandom_u32_state - 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 prandom_u32(). 50 */ 51 u32 prandom_u32_state(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(prandom_u32_state); 62 63 /** 64 * prandom_u32 - 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 prandom_u32(void) 71 { 72 unsigned long r; 73 struct rnd_state *state = &get_cpu_var(net_rand_state); 74 r = prandom_u32_state(state); 75 put_cpu_var(state); 76 return r; 77 } 78 EXPORT_SYMBOL(prandom_u32); 79 80 /* 81 * prandom_bytes_state - get the requested number of pseudo-random bytes 82 * 83 * @state: pointer to state structure holding seeded state. 84 * @buf: where to copy the pseudo-random bytes to 85 * @bytes: the requested number of bytes 86 * 87 * This is used for pseudo-randomness with no outside seeding. 88 * For more random results, use prandom_bytes(). 89 */ 90 void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes) 91 { 92 unsigned char *p = buf; 93 int i; 94 95 for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) { 96 u32 random = prandom_u32_state(state); 97 int j; 98 99 for (j = 0; j < sizeof(u32); j++) { 100 p[i + j] = random; 101 random >>= BITS_PER_BYTE; 102 } 103 } 104 if (i < bytes) { 105 u32 random = prandom_u32_state(state); 106 107 for (; i < bytes; i++) { 108 p[i] = random; 109 random >>= BITS_PER_BYTE; 110 } 111 } 112 } 113 EXPORT_SYMBOL(prandom_bytes_state); 114 115 /** 116 * prandom_bytes - get the requested number of pseudo-random bytes 117 * @buf: where to copy the pseudo-random bytes to 118 * @bytes: the requested number of bytes 119 */ 120 void prandom_bytes(void *buf, int bytes) 121 { 122 struct rnd_state *state = &get_cpu_var(net_rand_state); 123 124 prandom_bytes_state(state, buf, bytes); 125 put_cpu_var(state); 126 } 127 EXPORT_SYMBOL(prandom_bytes); 128 129 /** 130 * prandom_seed - add entropy to pseudo random number generator 131 * @seed: seed value 132 * 133 * Add some additional seeding to the prandom pool. 134 */ 135 void prandom_seed(u32 entropy) 136 { 137 int i; 138 /* 139 * No locking on the CPUs, but then somewhat random results are, well, 140 * expected. 141 */ 142 for_each_possible_cpu (i) { 143 struct rnd_state *state = &per_cpu(net_rand_state, i); 144 state->s1 = __seed(state->s1 ^ entropy, 1); 145 } 146 } 147 EXPORT_SYMBOL(prandom_seed); 148 149 /* 150 * Generate some initially weak seeding values to allow 151 * to start the prandom_u32() engine. 152 */ 153 static int __init prandom_init(void) 154 { 155 int i; 156 157 for_each_possible_cpu(i) { 158 struct rnd_state *state = &per_cpu(net_rand_state,i); 159 160 #define LCG(x) ((x) * 69069) /* super-duper LCG */ 161 state->s1 = __seed(LCG(i + jiffies), 1); 162 state->s2 = __seed(LCG(state->s1), 7); 163 state->s3 = __seed(LCG(state->s2), 15); 164 165 /* "warm it up" */ 166 prandom_u32_state(state); 167 prandom_u32_state(state); 168 prandom_u32_state(state); 169 prandom_u32_state(state); 170 prandom_u32_state(state); 171 prandom_u32_state(state); 172 } 173 return 0; 174 } 175 core_initcall(prandom_init); 176 177 /* 178 * Generate better values after random number generator 179 * is fully initialized. 180 */ 181 static int __init prandom_reseed(void) 182 { 183 int i; 184 185 for_each_possible_cpu(i) { 186 struct rnd_state *state = &per_cpu(net_rand_state,i); 187 u32 seeds[3]; 188 189 get_random_bytes(&seeds, sizeof(seeds)); 190 state->s1 = __seed(seeds[0], 1); 191 state->s2 = __seed(seeds[1], 7); 192 state->s3 = __seed(seeds[2], 15); 193 194 /* mix it in */ 195 prandom_u32_state(state); 196 } 197 return 0; 198 } 199 late_initcall(prandom_reseed); 200