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v/vlib/rand/splitmix64.v

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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 += u64(0x9e3779b97f4a7c15)
mut z := rng.state
z = (z ^ u64((z >> u64(30)))) * u64(0xbf58476d1ce4e5b9)
z = (z ^ u64((z >> u64(27)))) * u64(0x94d049bb133111eb)
return z ^ u64(z >> u64(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 := u64( -bound % bound )
for {
r := rng.next()
if r >= threshold {
return u64( r % bound )
}
}
return u64(0)
}