oxedyne/ore — oracle/src/random.rs

1.1 KiB, 1 run

created by r2848102244:91, which is this file's identity for as long as the history lasts, whatever it is later renamed to

1	//! A tiny deterministic generator, so that a failing seed can be replayed.
2
3	/// SplitMix64.
4	pub struct Rng {
5	state: u64,
6	}
7
8	impl Rng {
9	/// Creates a generator from a seed.
10	pub fn new(seed: u64) -> Self {
11	Self { state: seed.wrapping_add(0x9E3779B97F4A7C15) }
12	}
13
14	/// The next 64 bits.
15	pub fn next(&mut self) -> u64 {
16	self.state = self.state.wrapping_add(0x9E3779B97F4A7C15);
17	let mut z = self.state;
18	z = (z ^ (z >> 30)).wrapping_mul(0xBF58476D1CE4E5B9);
19	z = (z ^ (z >> 27)).wrapping_mul(0x94D049BB133111EB);
20	z ^ (z >> 31)
21	}
22
23	/// A number below `n`, or zero when `n` is zero.
24	pub fn below(&mut self, n: usize) -> usize {
25	if n == 0 {
26	0
27	} else {
28	(self.next() % n as u64) as usize
29	}
30	}
31
32	/// A number in `lo..=hi`.
33	pub fn between(&mut self, lo: usize, hi: usize) -> usize {
34	if hi <= lo {
35	lo
36	} else {
37	lo + self.below(hi - lo + 1)
38	}
39	}
40
41	/// True with probability `num/den`.
42	pub fn chance(&mut self, num: u64, den: u64) -> bool {
43	self.next() % den < num
44	}
45
46	/// Shuffles a slice in place.
47	pub fn shuffle<T>(&mut self, v: &mut [T]) {
48	for i in (1..v.len()).rev() {
49	let j = self.below(i + 1);
50	v.swap(i, j);
51	}
52	}
53	}