rand_xoshiro/
xoroshiro64star.rs

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1// Copyright 2018 Developers of the Rand project.
2//
3// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
4// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
5// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
6// option. This file may not be copied, modified, or distributed
7// except according to those terms.
8
9use byteorder::{ByteOrder, LittleEndian};
10use rand_core;
11use rand_core::le::read_u32_into;
12use rand_core::impls::{fill_bytes_via_next, next_u64_via_u32};
13use rand_core::{RngCore, SeedableRng};
14
15/// A xoroshiro64* random number generator.
16///
17/// The xoroshiro64* algorithm is not suitable for cryptographic purposes, but
18/// is very fast and has good statistical properties, besides a low linear
19/// complexity in the lowest bits.
20///
21/// The algorithm used here is translated from [the `xoroshiro64star.c`
22/// reference source code](http://xoshiro.di.unimi.it/xoroshiro64star.c) by
23/// David Blackman and Sebastiano Vigna.
24#[allow(missing_copy_implementations)]
25#[derive(Debug, Clone)]
26pub struct Xoroshiro64Star {
27    s0: u32,
28    s1: u32,
29}
30
31impl RngCore for Xoroshiro64Star {
32    #[inline]
33    fn next_u32(&mut self) -> u32 {
34        let r = self.s0.wrapping_mul(0x9E3779BB);
35        impl_xoroshiro_u32!(self);
36        r
37    }
38
39    #[inline]
40    fn next_u64(&mut self) -> u64 {
41        next_u64_via_u32(self)
42    }
43
44    #[inline]
45    fn fill_bytes(&mut self, dest: &mut [u8]) {
46        fill_bytes_via_next(self, dest);
47    }
48
49    #[inline]
50    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand_core::Error> {
51        self.fill_bytes(dest);
52        Ok(())
53    }
54}
55
56impl SeedableRng for Xoroshiro64Star {
57    type Seed = [u8; 8];
58
59    /// Create a new `Xoroshiro64Star`.  If `seed` is entirely 0, it will be
60    /// mapped to a different seed.
61    fn from_seed(seed: [u8; 8]) -> Xoroshiro64Star {
62        deal_with_zero_seed!(seed, Self);
63        let mut s = [0; 2];
64        read_u32_into(&seed, &mut s);
65
66        Xoroshiro64Star {
67            s0: s[0],
68            s1: s[1],
69        }
70    }
71
72    /// Seed a `Xoroshiro64Star` from a `u64` using `SplitMix64`.
73    fn seed_from_u64(seed: u64) -> Xoroshiro64Star {
74        let mut s = [0; 8];
75        LittleEndian::write_u64(&mut s, seed);
76        Xoroshiro64Star::from_seed(s)
77    }
78}
79
80#[cfg(test)]
81mod tests {
82    use super::*;
83
84    #[test]
85    fn reference() {
86        let mut rng = Xoroshiro64Star::from_seed([1, 0, 0, 0, 2, 0, 0, 0]);
87        // These values were produced with the reference implementation:
88        // http://xoshiro.di.unimi.it/xoshiro64star.c
89        let expected = [
90            2654435771, 327208753, 4063491769, 4259754937, 261922412, 168123673,
91            552743735, 1672597395, 1031040050, 2755315674,
92        ];
93        for &e in &expected {
94            assert_eq!(rng.next_u32(), e);
95        }
96    }
97}
rand_xoshiro/xoroshiro64star.rs

rand_xoshiro/
xoroshiro64star.rs
