mt19937_u64.c

// clang-format off
u64 mt19937_u64(void)
{
#define NN 312
#define MM 156
#define MATRIX_A 0xB5026F5AA96619E9ULL
// Most significant 33 bits
#define UM 0xFFFFFFFF80000000ULL
// Least significant 31 bits
#define LM 0x7FFFFFFFULL
	static u64 mag01[2] = { 0ULL, MATRIX_A };
	// The array for the state vector
	static u64 mt[NN];
	// mti==NN+1 means mt[NN] is not initialized
	static int mti = NN + 1;
	if (mti >= NN) {
		// generate NN words at one time
		// if init_genrand64() has not been called,
		// a default initial seed 5489ULL is used
		if (mti == NN + 1) {
			mt[0] = 0x990124ULL;
			for (mti = 1; mti < NN; mti++) {
				mt[mti] = 6364136223846793005ULL * (mt[mti - 1] ^ (mt[mti - 1] >> 62)) + mti;
			}
		}
		for (int i = 0; i < NN - MM; i++) {
			u64 x = (mt[i] & UM) | (mt[i + 1] & LM);
			mt[i] = mt[i + MM] ^ (x >> 1) ^ mag01[x & 1ULL];
		}
		for (int i = NN - MM; i < NN - 1; i++) {
			u64 x = (mt[i] & UM) | (mt[i + 1] & LM);
			mt[i] = mt[i + (MM - NN)] ^ (x >> 1) ^ mag01[x & 1ULL];
		}
		u64 x = (mt[NN - 1] & UM) | (mt[0] & LM);
		mt[NN - 1] = mt[MM - 1] ^ (x >> 1) ^ mag01[x & 1ULL];
		mti = 0;
	}
	u64 x = mt[mti++];
	x ^= (x >> 29) & 0x5555555555555555ULL; x ^= (x << 17) & 0x71D67FFFEDA60000ULL;
	x ^= (x << 37) & 0xFFF7EEE000000000ULL; x ^= (x >> 43);
	return x;
}
// clang-format on