FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/vdev_draid_rand.c

     /*
      * Xorshift Pseudo Random Number Generator based on work by David Blackman
      * and Sebastiano Vigna (vigna@acm.org).
      *
      *   "Further scramblings of Marsaglia's xorshift generators"
      *   http://vigna.di.unimi.it/ftp/papers/xorshiftplus.pdf
      *   http://prng.di.unimi.it/xoroshiro128plusplus.c
      *
      * To the extent possible under law, the author has dedicated all copyright
     * and related and neighboring rights to this software to the public domain
     * worldwide. This software is distributed without any warranty.
     *
     * See <http://creativecommons.org/publicdomain/zero/1.0/>.
     *
     * This is xoroshiro128++ 1.0, one of our all-purpose, rock-solid,
     * small-state generators. It is extremely (sub-ns) fast and it passes all
     * tests we are aware of, but its state space is large enough only for
     * mild parallelism.
     */
    
    #include <sys/vdev_draid.h>
    
    static inline uint64_t rotl(const uint64_t x, int k)
    {
            return (x << k) | (x >> (64 - k));
    }
    
    uint64_t
    vdev_draid_rand(uint64_t *s)
    {
            const uint64_t s0 = s[0];
            uint64_t s1 = s[1];
            const uint64_t result = rotl(s0 + s1, 17) + s0;
    
            s1 ^= s0;
            s[0] = rotl(s0, 49) ^ s1 ^ (s1 << 21); // a, b
            s[1] = rotl(s1, 28); // c
    
            return (result);
    }

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