rand_xoshiro/
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
9use rand_core::impls::fill_bytes_via_next;
10use rand_core::le::read_u64_into;
11use rand_core::{RngCore, SeedableRng};
12#[cfg(feature = "serde")]
13use serde::{Deserialize, Serialize};
14
15/// A xoshiro256++ random number generator.
16///
17/// The xoshiro256++ algorithm is not suitable for cryptographic purposes, but
18/// is very fast and has excellent statistical properties.
19///
20/// The algorithm used here is translated from [the `xoshiro256plusplus.c`
21/// reference source code](http://xoshiro.di.unimi.it/xoshiro256plusplus.c) by
22/// David Blackman and Sebastiano Vigna.
23#[derive(Debug, Clone, PartialEq, Eq)]
24#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
25pub struct Xoshiro256PlusPlus {
26    s: [u64; 4],
27}
28
29impl Xoshiro256PlusPlus {
30    /// Jump forward, equivalently to 2^128 calls to `next_u64()`.
31    ///
32    /// This can be used to generate 2^128 non-overlapping subsequences for
33    /// parallel computations.
34    ///
35    /// ```
36    /// use rand_xoshiro::rand_core::SeedableRng;
37    /// use rand_xoshiro::Xoshiro256PlusPlus;
38    ///
39    /// let rng1 = Xoshiro256PlusPlus::seed_from_u64(0);
40    /// let mut rng2 = rng1.clone();
41    /// rng2.jump();
42    /// let mut rng3 = rng2.clone();
43    /// rng3.jump();
44    /// ```
45    pub fn jump(&mut self) {
46        impl_jump!(
47            u64,
48            self,
49            [
50                0x180ec6d33cfd0aba,
51                0xd5a61266f0c9392c,
52                0xa9582618e03fc9aa,
53                0x39abdc4529b1661c
54            ]
55        );
56    }
57
58    /// Jump forward, equivalently to 2^192 calls to `next_u64()`.
59    ///
60    /// This can be used to generate 2^64 starting points, from each of which
61    /// `jump()` will generate 2^64 non-overlapping subsequences for parallel
62    /// distributed computations.
63    pub fn long_jump(&mut self) {
64        impl_jump!(
65            u64,
66            self,
67            [
68                0x76e15d3efefdcbbf,
69                0xc5004e441c522fb3,
70                0x77710069854ee241,
71                0x39109bb02acbe635
72            ]
73        );
74    }
75}
76
77impl SeedableRng for Xoshiro256PlusPlus {
78    type Seed = [u8; 32];
79
80    /// Create a new `Xoshiro256PlusPlus`.  If `seed` is entirely 0, it will be
81    /// mapped to a different seed.
82    #[inline]
83    fn from_seed(seed: [u8; 32]) -> Xoshiro256PlusPlus {
84        deal_with_zero_seed!(seed, Self);
85        let mut state = [0; 4];
86        read_u64_into(&seed, &mut state);
87        Xoshiro256PlusPlus { s: state }
88    }
89
90    /// Seed a `Xoshiro256PlusPlus` from a `u64` using `SplitMix64`.
91    fn seed_from_u64(seed: u64) -> Xoshiro256PlusPlus {
92        from_splitmix!(seed)
93    }
94}
95
96impl RngCore for Xoshiro256PlusPlus {
97    #[inline]
98    fn next_u32(&mut self) -> u32 {
99        // The lowest bits have some linear dependencies, so we use the
100        // upper bits instead.
101        (self.next_u64() >> 32) as u32
102    }
103
104    #[inline]
105    fn next_u64(&mut self) -> u64 {
106        let result_plusplus = plusplus_u64!(self.s[0], self.s[3], 23);
107        impl_xoshiro_u64!(self);
108        result_plusplus
109    }
110
111    #[inline]
112    fn fill_bytes(&mut self, dest: &mut [u8]) {
113        fill_bytes_via_next(self, dest);
114    }
115}
116
117#[cfg(test)]
118mod tests {
119    use super::*;
120
121    #[test]
122    fn reference() {
123        let mut rng = Xoshiro256PlusPlus::from_seed([
124            1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0,
125            0, 0, 0,
126        ]);
127        // These values were produced with the reference implementation:
128        // http://xoshiro.di.unimi.it/xoshiro256plusplus.c
129        let expected = [
130            41943041,
131            58720359,
132            3588806011781223,
133            3591011842654386,
134            9228616714210784205,
135            9973669472204895162,
136            14011001112246962877,
137            12406186145184390807,
138            15849039046786891736,
139            10450023813501588000,
140        ];
141        for &e in &expected {
142            assert_eq!(rng.next_u64(), e);
143        }
144    }
145}
rand_xoshiro/xoshiro256plusplus.rs

rand_xoshiro/
xoshiro256plusplus.rs
