source: libcfa/src/bits/random.hfa @ 6047b00

#pragma once

#include <stdint.h>

//--------------------------------------------------
#if defined(__SIZEOF_INT128__)
        typedef __uint128_t __lehmer64_state_t;
        static inline uint64_t __lehmer64( __lehmer64_state_t & state ) {
                state *= 0xda942042e4dd58b5;
                return state >> 64;
        }

//--------------------------------------------------
        typedef uint64_t __wyhash64_state_t;
        static inline uint64_t __wyhash64( __wyhash64_state_t & state ) {
                state += 0x60bee2bee120fc15;
                __uint128_t tmp;
                tmp = (__uint128_t) state * 0xa3b195354a39b70d;
                uint64_t m1 = (tmp >> 64) ^ tmp;
                tmp = (__uint128_t)m1 * 0x1b03738712fad5c9;
                uint64_t m2 = (tmp >> 64) ^ tmp;
                return m2;
        }
#endif

//--------------------------------------------------
typedef uint64_t __xorshift64_state_t;
static inline uint64_t __xorshift64( __xorshift64_state_t & state ) {
        uint64_t x = state;
        x ^= x << 13;
        x ^= x >> 7;
        x ^= x << 17;
        return state = x;
}

//--------------------------------------------------
typedef struct {
  uint32_t a, b, c, d;
  uint32_t counter;
} __xorwow__state_t;

/* The state array must be initialized to not be all zero in the first four words */
static inline uint32_t __xorwow( __xorwow__state_t & state ) {
        /* Algorithm "xorwow" from p. 5 of Marsaglia, "Xorshift RNGs" */
        uint32_t t = state.d;

        uint32_t const s = state.a;
        state.d = state.c;
        state.c = state.b;
        state.b = s;

        t ^= t >> 2;
        t ^= t << 1;
        t ^= s ^ (s << 4);
        state.a = t;

        state.counter += 362437;
        return t + state.counter;
}