mirror of
https://github.com/vlang/v.git
synced 2023-08-10 21:13:21 +03:00
69 lines
1.8 KiB
V
69 lines
1.8 KiB
V
module rand
|
|
// Ported from http://www.pcg-random.org/download.html
|
|
// and https://github.com/imneme/pcg-c-basic/blob/master/pcg_basic.c
|
|
pub struct Pcg32 {
|
|
mut:
|
|
state u64
|
|
inc u64
|
|
}
|
|
|
|
/**
|
|
* new_pcg32 - a Pcg32 PRNG generator
|
|
* @param initstate - the initial state of the PRNG.
|
|
* @param initseq - the stream/step of the PRNG.
|
|
* @return a new Pcg32 PRNG instance
|
|
*/
|
|
|
|
|
|
pub fn new_pcg32(initstate u64, initseq u64) Pcg32 {
|
|
mut rng := Pcg32{
|
|
}
|
|
rng.state = u64(0)
|
|
rng.inc = (initseq<<u64(1)) | u64(1)
|
|
rng.next()
|
|
rng.state += initstate
|
|
rng.next()
|
|
return rng
|
|
}
|
|
|
|
/**
|
|
* Pcg32.next - update the PRNG state and get back the next random number
|
|
* @return the generated pseudo random number
|
|
*/
|
|
|
|
|
|
[inline]
|
|
pub fn (mut rng Pcg32) next() u32 {
|
|
oldstate := rng.state
|
|
rng.state = oldstate * (6364136223846793005) + rng.inc
|
|
xorshifted := u32(((oldstate>>u64(18)) ^ oldstate)>>u64(27))
|
|
rot := u32(oldstate>>u64(59))
|
|
return ((xorshifted>>rot) | (xorshifted<<((-rot) & u32(31))))
|
|
}
|
|
|
|
/**
|
|
* Pcg32.bounded_next - update the PRNG state. Get the next number < bound
|
|
* @param bound - the returned random number will be < bound
|
|
* @return the generated pseudo random number
|
|
*/
|
|
|
|
|
|
[inline]
|
|
pub fn (mut rng Pcg32) bounded_next(bound u32) u32 {
|
|
// To avoid bias, we need to make the range of the RNG a multiple of
|
|
// bound, which we do by dropping output less than a threshold.
|
|
threshold := (-bound % bound)
|
|
// Uniformity guarantees that loop below will terminate. In practice, it
|
|
// should usually terminate quickly; on average (assuming all bounds are
|
|
// equally likely), 82.25% of the time, we can expect it to require just
|
|
// one iteration. In practice, bounds are typically small and only a
|
|
// tiny amount of the range is eliminated.
|
|
for {
|
|
r := rng.next()
|
|
if r >= threshold {
|
|
return (r % bound)
|
|
}
|
|
}
|
|
return u32(0)
|
|
}
|