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
23static inline uint64_t rotl(const uint64_t x, int k)
24{
25	return (x << k) | (x >> (64 - k));
26}
27
28uint64_t
29vdev_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}
41