xoroshiro.h

/*
 * xoroshiro128_plus functions have the following copyright:
 *
 * Written in 2016-2018 by David Blackman and Sebastiano Vigna (vigna@acm.org)
 * 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/>.
 */

#include <stdint.h>

extern void xoroshiro128plus_init(uint64_t *s, uint64_t seed);

static inline uint64_t
rotl(const uint64_t x, int k)
{
    return (x << k) | (x >> (64 - k));
}

static inline uint64_t
xoroshiro128plus(uint64_t *s)
{
    const uint64_t s0 = s[0];
    uint64_t s1 = s[1];
    const uint64_t result = s0 + s1;

    s1 ^= s0;
    s[0] = rotl(s0, 24) ^ s1 ^ (s1 << 16); // a, b
    s[1] = rotl(s1, 37); // c

    return result;
}