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 rand_core::impls::{fill_bytes_via_next, next_u64_via_u32};
10use rand_core::le::read_u32_into;
11use rand_core::{RngCore, SeedableRng};
12#[cfg(feature = "serde")]
13use serde::{Deserialize, Serialize};
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, PartialEq, Eq)]
26#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
27pub struct Xoroshiro64Star {
28 s0: u32,
29 s1: u32,
30}
31
32impl RngCore for Xoroshiro64Star {
33 #[inline]
34 fn next_u32(&mut self) -> u32 {
35 let r: u32 = self.s0.wrapping_mul(0x9E3779BB);
36 impl_xoroshiro_u32!(self);
37 r
38 }
39
40 #[inline]
41 fn next_u64(&mut self) -> u64 {
42 next_u64_via_u32(self)
43 }
44
45 #[inline]
46 fn fill_bytes(&mut self, dest: &mut [u8]) {
47 fill_bytes_via_next(self, dest);
48 }
49}
50
51impl SeedableRng for Xoroshiro64Star {
52 type Seed = [u8; 8];
53
54 /// Create a new `Xoroshiro64Star`. If `seed` is entirely 0, it will be
55 /// mapped to a different seed.
56 fn from_seed(seed: [u8; 8]) -> Xoroshiro64Star {
57 deal_with_zero_seed!(seed, Self, 8);
58 let mut s: [u32; 2] = [0; 2];
59 read_u32_into(&seed, &mut s);
60
61 Xoroshiro64Star { s0: s[0], s1: s[1] }
62 }
63
64 /// Seed a `Xoroshiro64Star` from a `u64` using `SplitMix64`.
65 fn seed_from_u64(seed: u64) -> Xoroshiro64Star {
66 from_splitmix!(seed)
67 }
68}
69
70#[cfg(test)]
71mod tests {
72 use super::*;
73
74 #[test]
75 fn reference() {
76 let mut rng = Xoroshiro64Star::from_seed([1, 0, 0, 0, 2, 0, 0, 0]);
77 // These values were produced with the reference implementation:
78 // http://xoshiro.di.unimi.it/xoshiro64star.c
79 let expected = [
80 2654435771, 327208753, 4063491769, 4259754937, 261922412, 168123673, 552743735,
81 1672597395, 1031040050, 2755315674,
82 ];
83 for &e in &expected {
84 assert_eq!(rng.next_u32(), e);
85 }
86 }
87
88 #[test]
89 fn zero_seed() {
90 let mut rng = Xoroshiro64Star::seed_from_u64(0);
91 assert_ne!(rng.next_u64(), 0);
92 }
93}
94