54 lines
1.0 KiB
V
54 lines
1.0 KiB
V
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)
|
|
}
|
|
|