Jens Axboe | 79c94bd | 2010-03-25 23:13:32 +0100 | [diff] [blame^] | 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 | |
Jens Axboe | 1fbbf72 | 2010-03-25 23:03:18 +0100 | [diff] [blame] | 36 | #include "rand.h" |
| 37 | |
| 38 | struct frand_state __fio_rand_state; |
| 39 | |
| 40 | static inline int __seed(unsigned int x, unsigned int m) |
| 41 | { |
| 42 | return (x < m) ? x + m : x; |
| 43 | } |
| 44 | |
| 45 | void init_rand(struct frand_state *state) |
| 46 | { |
| 47 | #define LCG(x) ((x) * 69069) /* super-duper LCG */ |
| 48 | |
| 49 | state->s1 = __seed(LCG((2^31) + (2^17) + (2^7)), 1); |
| 50 | state->s2 = __seed(LCG(state->s1), 7); |
| 51 | state->s3 = __seed(LCG(state->s2), 15); |
| 52 | |
| 53 | __rand(state); |
| 54 | __rand(state); |
| 55 | __rand(state); |
| 56 | __rand(state); |
| 57 | __rand(state); |
| 58 | __rand(state); |
| 59 | } |