rand_xoshiro/
xoroshiro128plus.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::le::read_u64_into;
11use rand_core::impls::fill_bytes_via_next;
12use rand_core::{RngCore, SeedableRng};
13
14/// A xoroshiro128+ random number generator.
15///
16/// The xoroshiro128+ algorithm is not suitable for cryptographic purposes, but
17/// is very fast and has good statistical properties, besides a low linear
18/// complexity in the lowest bits.
19///
20/// The algorithm used here is translated from [the `xoroshiro128plus.c`
21/// reference source code](http://xoshiro.di.unimi.it/xoroshiro128plus.c) by
22/// David Blackman and Sebastiano Vigna.
23#[allow(missing_copy_implementations)]
24#[derive(Debug, Clone, PartialEq, Eq)]
25#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
26pub struct Xoroshiro128Plus {
27    s0: u64,
28    s1: u64,
29}
30
31impl Xoroshiro128Plus {
32    /// Jump forward, equivalently to 2^64 calls to `next_u64()`.
33    ///
34    /// This can be used to generate 2^64 non-overlapping subsequences for
35    /// parallel computations.
36    ///
37    /// ```
38    /// use rand_xoshiro::rand_core::SeedableRng;
39    /// use rand_xoshiro::Xoroshiro128Plus;
40    ///
41    /// let rng1 = Xoroshiro128Plus::seed_from_u64(0);
42    /// let mut rng2 = rng1.clone();
43    /// rng2.jump();
44    /// let mut rng3 = rng2.clone();
45    /// rng3.jump();
46    /// ```
47    pub fn jump(&mut self) {
48        impl_jump!(u64, self, [0xdf900294d8f554a5, 0x170865df4b3201fc]);
49    }
50
51    /// Jump forward, equivalently to 2^96 calls to `next_u64()`.
52    ///
53    /// This can be used to generate 2^32 starting points, from each of which
54    /// `jump()` will generate 2^32 non-overlapping subsequences for parallel
55    /// distributed computations.
56    pub fn long_jump(&mut self) {
57        impl_jump!(u64, self, [0xd2a98b26625eee7b, 0xdddf9b1090aa7ac1]);
58    }
59}
60
61impl RngCore for Xoroshiro128Plus {
62    #[inline]
63    fn next_u32(&mut self) -> u32 {
64        // The two 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 r = self.s0.wrapping_add(self.s1);
72        impl_xoroshiro_u64!(self);
73        r
74    }
75
76    #[inline]
77    fn fill_bytes(&mut self, dest: &mut [u8]) {
78        fill_bytes_via_next(self, dest);
79    }
80
81    #[inline]
82    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand_core::Error> {
83        self.fill_bytes(dest);
84        Ok(())
85    }
86}
87
88impl SeedableRng for Xoroshiro128Plus {
89    type Seed = [u8; 16];
90
91    /// Create a new `Xoroshiro128Plus`.  If `seed` is entirely 0, it will be
92    /// mapped to a different seed.
93    fn from_seed(seed: [u8; 16]) -> Xoroshiro128Plus {
94        deal_with_zero_seed!(seed, Self);
95        let mut s = [0; 2];
96        read_u64_into(&seed, &mut s);
97
98        Xoroshiro128Plus {
99            s0: s[0],
100            s1: s[1],
101        }
102    }
103
104    /// Seed a `Xoroshiro128Plus` from a `u64` using `SplitMix64`.
105    fn seed_from_u64(seed: u64) -> Xoroshiro128Plus {
106        from_splitmix!(seed)
107    }
108}
109
110#[cfg(test)]
111mod tests {
112    use super::*;
113
114    #[test]
115    fn reference() {
116        let mut rng = Xoroshiro128Plus::from_seed(
117            [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0]);
118        // These values were produced with the reference implementation:
119        // http://xoshiro.di.unimi.it/xoshiro128starstar.c
120        let expected = [
121            3, 412333834243, 2360170716294286339, 9295852285959843169,
122            2797080929874688578, 6019711933173041966, 3076529664176959358,
123            3521761819100106140, 7493067640054542992, 920801338098114767,
124        ];
125        for &e in &expected {
126            assert_eq!(rng.next_u64(), e);
127        }
128    }
129}
rand_xoshiro/xoroshiro128plus.rs

rand_xoshiro/
xoroshiro128plus.rs
