module rand
// Ported from http://xoshiro.di.unimi.it/splitmix64.c
struct Splitmix64 {
mut:
	state u64
}

/**
 * new_splitmix64 - a Splitmix64 PRNG generator
 * @param seed the initial seed of the PRNG.
 * @return a new Splitmix64 PRNG instance
*/


pub fn new_splitmix64(seed u64) Splitmix64 {
	return Splitmix64{
		seed}
}

/**
 * Splitmix64.next - update the PRNG state and get back the next random number
 * @return the generated pseudo random number
*/


[inline]
pub fn (rng mut Splitmix64) next() u64 {
	rng.state += (0x9e3779b97f4a7c15)
	mut z := rng.state
	z = (z ^ ((z>>u64(30)))) * (0xbf58476d1ce4e5b9)
	z = (z ^ ((z>>u64(27)))) * (0x94d049bb133111eb)
	return z ^ (z>>(31))
}

/**
 * Splitmix64.bounded_next - Get the next random number < bound
 * @param bound - the returned random number will be < bound
 * @return the generated pseudo random number
*/


[inline]
pub fn (rng mut Splitmix64) bounded_next(bound u64) u64 {
	threshold := -bound % bound
	for {
		r := rng.next()
		if r >= threshold {
			return r % bound
		}
	}
	return u64(0)
}