Bruno BELANYI
93d255623b
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This is a higher quality source of randomness than a XOR-shift generator, while still being fast and easy to write.
50 lines
1.2 KiB
Rust
50 lines
1.2 KiB
Rust
/// A trait to represent RNG for u64 values.
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pub trait RandGen {
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fn gen(&mut self) -> u64;
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}
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// A simple pcg64_fast RNG implementation, for code-generation.
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#[cfg(test)]
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pub struct SimpleRng(u128);
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#[cfg(test)]
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impl SimpleRng {
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pub fn new() -> Self {
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Self(0xcafef00dd15ea5e5 | 1) // https://xkcd.com/221/
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}
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pub fn gen(&mut self) -> u64 {
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const MULTIPLIER: u128 = 0x2360_ED05_1FC6_5DA4_4385_DF64_9FCC_F645;
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const XSHIFT: u32 = 64; // (128 - 64 + 64) / 2
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const ROTATE: u32 = 122; // 128 - 6
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self.0 = self.0.wrapping_mul(MULTIPLIER);
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let rot = (self.0 >> ROTATE) as u32;
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let xsl = (self.0 >> XSHIFT) as u64 ^ (self.0 as u64);
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xsl.rotate_right(rot)
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}
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}
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#[cfg(test)]
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impl RandGen for SimpleRng {
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fn gen(&mut self) -> u64 {
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self.gen()
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}
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}
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#[cfg(test)]
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mod test {
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use super::*;
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#[test]
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fn rng() {
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let mut rng = SimpleRng::new();
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assert_eq!(rng.gen(), 64934999470316615);
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assert_eq!(rng.gen(), 15459456780870779090);
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assert_eq!(rng.gen(), 13715484424881807779);
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assert_eq!(rng.gen(), 17718572936700675021);
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assert_eq!(rng.gen(), 14587996314750246637);
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}
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}
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