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1 | /* |
2 | * Xorshift Pseudo Random Number Generator based on work by David Blackman | |
3 | * and Sebastiano Vigna (vigna@acm.org). | |
4 | * | |
5 | * "Further scramblings of Marsaglia's xorshift generators" | |
6 | * http://vigna.di.unimi.it/ftp/papers/xorshiftplus.pdf | |
7 | * http://prng.di.unimi.it/xoroshiro128plusplus.c | |
8 | * | |
9 | * To the extent possible under law, the author has dedicated all copyright | |
10 | * and related and neighboring rights to this software to the public domain | |
11 | * worldwide. This software is distributed without any warranty. | |
12 | * | |
13 | * See <http://creativecommons.org/publicdomain/zero/1.0/>. | |
14 | * | |
15 | * This is xoroshiro128++ 1.0, one of our all-purpose, rock-solid, | |
16 | * small-state generators. It is extremely (sub-ns) fast and it passes all | |
17 | * tests we are aware of, but its state space is large enough only for | |
18 | * mild parallelism. | |
19 | */ | |
20 | ||
21 | #include <sys/vdev_draid.h> | |
22 | ||
23 | static inline uint64_t rotl(const uint64_t x, int k) | |
24 | { | |
25 | return (x << k) | (x >> (64 - k)); | |
26 | } | |
27 | ||
28 | uint64_t | |
29 | vdev_draid_rand(uint64_t *s) | |
30 | { | |
31 | const uint64_t s0 = s[0]; | |
32 | uint64_t s1 = s[1]; | |
33 | const uint64_t result = rotl(s0 + s1, 17) + s0; | |
34 | ||
35 | s1 ^= s0; | |
36 | s[0] = rotl(s0, 49) ^ s1 ^ (s1 << 21); // a, b | |
37 | s[1] = rotl(s1, 28); // c | |
38 | ||
39 | return (result); | |
40 | } |