rand_xoshiro/
xoroshiro64starstar.rs

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 core::convert::Infallible;
10use rand_core::{SeedableRng, TryRng, utils};
11#[cfg(feature = "serde")]
12use serde::{Deserialize, Serialize};
13
14/// A xoroshiro64** random number generator.
15///
16/// The xoshiro64** algorithm is not suitable for cryptographic purposes, but
17/// is very fast and has excellent statistical properties.
18///
19/// The algorithm used here is translated from [the `xoroshiro64starstar.c`
20/// reference source code](http://xoshiro.di.unimi.it/xoroshiro64starstar.c) by
21/// David Blackman and Sebastiano Vigna.
22#[allow(missing_copy_implementations)]
23#[derive(Debug, Clone, PartialEq, Eq)]
24#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
25pub struct Xoroshiro64StarStar {
26    s0: u32,
27    s1: u32,
28}
29
30impl TryRng for Xoroshiro64StarStar {
31    type Error = Infallible;
32
33    #[inline]
34    fn try_next_u32(&mut self) -> Result<u32, Self::Error> {
35        let r = starstar_u32!(self.s0);
36        impl_xoroshiro_u32!(self);
37        Ok(r)
38    }
39
40    #[inline]
41    fn try_next_u64(&mut self) -> Result<u64, Self::Error> {
42        utils::next_u64_via_u32(self)
43    }
44
45    #[inline]
46    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Self::Error> {
47        utils::fill_bytes_via_next_word(dest, || self.try_next_u32())
48    }
49}
50
51impl_state_pair!(Xoroshiro64StarStar, u32);
52
53impl SeedableRng for Xoroshiro64StarStar {
54    type Seed = [u8; 8];
55
56    /// Create a new `Xoroshiro64StarStar`.  If `seed` is entirely 0, it will be
57    /// mapped to a different seed.
58    fn from_seed(seed: [u8; 8]) -> Xoroshiro64StarStar {
59        let s: [_; 2] = utils::read_words(crate::common::zero_seed_fallback(&seed));
60
61        Xoroshiro64StarStar { s0: s[0], s1: s[1] }
62    }
63
64    /// Seed a `Xoroshiro64StarStar` from a `u64` using `SplitMix64`.
65    fn seed_from_u64(seed: u64) -> Xoroshiro64StarStar {
66        from_splitmix!(seed)
67    }
68}
69
70#[cfg(test)]
71mod tests {
72    use super::*;
73    use rand_core::Rng;
74
75    #[test]
76    fn reference() {
77        let mut rng = Xoroshiro64StarStar::from_seed([1, 0, 0, 0, 2, 0, 0, 0]);
78        // These values were produced with the reference implementation:
79        // http://xoshiro.di.unimi.it/xoshiro64starstar.c
80        let expected = [
81            3802928447, 813792938, 1618621494, 2955957307, 3252880261, 1129983909, 2539651700,
82            1327610908, 1757650787, 2763843748,
83        ];
84        for &e in &expected {
85            assert_eq!(rng.next_u32(), e);
86        }
87    }
88
89    #[test]
90    fn zero_seed() {
91        let mut rng = Xoroshiro64StarStar::seed_from_u64(0);
92        assert_ne!(rng.next_u64(), 0);
93    }
94
95    #[test]
96    fn zero_seed_maps_to_seed_from_u64_zero() {
97        let from_zero = Xoroshiro64StarStar::from_seed([0u8; 8]);
98        let from_sm0 = Xoroshiro64StarStar::seed_from_u64(0);
99        assert_eq!(from_zero, from_sm0);
100    }
101
102    #[test]
103    fn state_roundtrip() {
104        let rng = Xoroshiro64StarStar::seed_from_u64(42);
105        let clone = Xoroshiro64StarStar::from_seed(rng.state());
106        assert_eq!(clone, rng);
107    }
108}
rand_xoshiro/xoroshiro64starstar.rs

rand_xoshiro/
xoroshiro64starstar.rs
