rand/rngs/
xoshiro256plusplus.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
9#[cfg(feature="serde1")] use serde::{Serialize, Deserialize};
10use rand_core::impls::fill_bytes_via_next;
11use rand_core::le::read_u64_into;
12use rand_core::{SeedableRng, RngCore, Error};
13
14/// A xoshiro256++ random number generator.
15///
16/// The xoshiro256++ 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 `xoshiro256plusplus.c`
20/// reference source code](http://xoshiro.di.unimi.it/xoshiro256plusplus.c) by
21/// David Blackman and Sebastiano Vigna.
22#[derive(Debug, Clone, PartialEq, Eq)]
23#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
24pub struct Xoshiro256PlusPlus {
25    s: [u64; 4],
26}
27
28impl SeedableRng for Xoshiro256PlusPlus {
29    type Seed = [u8; 32];
30
31    /// Create a new `Xoshiro256PlusPlus`.  If `seed` is entirely 0, it will be
32    /// mapped to a different seed.
33    #[inline]
34    fn from_seed(seed: [u8; 32]) -> Xoshiro256PlusPlus {
35        if seed.iter().all(|&x| x == 0) {
36            return Self::seed_from_u64(0);
37        }
38        let mut state = [0; 4];
39        read_u64_into(&seed, &mut state);
40        Xoshiro256PlusPlus { s: state }
41    }
42
43    /// Create a new `Xoshiro256PlusPlus` from a `u64` seed.
44    ///
45    /// This uses the SplitMix64 generator internally.
46    fn seed_from_u64(mut state: u64) -> Self {
47        const PHI: u64 = 0x9e3779b97f4a7c15;
48        let mut seed = Self::Seed::default();
49        for chunk in seed.as_mut().chunks_mut(8) {
50            state = state.wrapping_add(PHI);
51            let mut z = state;
52            z = (z ^ (z >> 30)).wrapping_mul(0xbf58476d1ce4e5b9);
53            z = (z ^ (z >> 27)).wrapping_mul(0x94d049bb133111eb);
54            z = z ^ (z >> 31);
55            chunk.copy_from_slice(&z.to_le_bytes());
56        }
57        Self::from_seed(seed)
58    }
59}
60
61impl RngCore for Xoshiro256PlusPlus {
62    #[inline]
63    fn next_u32(&mut self) -> u32 {
64        // The lowest bits have some linear dependencies, so we use the
65        // upper bits instead.
66        (self.next_u64() >> 32) as u32
67    }
68
69    #[inline]
70    fn next_u64(&mut self) -> u64 {
71        let result_plusplus = self.s[0]
72            .wrapping_add(self.s[3])
73            .rotate_left(23)
74            .wrapping_add(self.s[0]);
75
76        let t = self.s[1] << 17;
77
78        self.s[2] ^= self.s[0];
79        self.s[3] ^= self.s[1];
80        self.s[1] ^= self.s[2];
81        self.s[0] ^= self.s[3];
82
83        self.s[2] ^= t;
84
85        self.s[3] = self.s[3].rotate_left(45);
86
87        result_plusplus
88    }
89
90    #[inline]
91    fn fill_bytes(&mut self, dest: &mut [u8]) {
92        fill_bytes_via_next(self, dest);
93    }
94
95    #[inline]
96    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
97        self.fill_bytes(dest);
98        Ok(())
99    }
100}
101
102#[cfg(test)]
103mod tests {
104    use super::*;
105
106    #[test]
107    fn reference() {
108        let mut rng = Xoshiro256PlusPlus::from_seed(
109            [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0,
110             3, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0]);
111        // These values were produced with the reference implementation:
112        // http://xoshiro.di.unimi.it/xoshiro256plusplus.c
113        let expected = [
114            41943041, 58720359, 3588806011781223, 3591011842654386,
115            9228616714210784205, 9973669472204895162, 14011001112246962877,
116            12406186145184390807, 15849039046786891736, 10450023813501588000,
117        ];
118        for &e in &expected {
119            assert_eq!(rng.next_u64(), e);
120        }
121    }
122}
rand/rngs/xoshiro256plusplus.rs

rand/rngs/
xoshiro256plusplus.rs
