rand_xoshiro/
xoshiro128plus.rs

Help
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::{next_u64_via_u32, fill_bytes_via_next};
10use rand_core::le::read_u32_into;
11use rand_core::{SeedableRng, RngCore, Error};
12
13/// A xoshiro128+ random number generator.
14///
15/// The xoshiro128+ algorithm is not suitable for cryptographic purposes, but
16/// is very fast and has good statistical properties, besides a low linear
17/// complexity in the lowest bits.
18///
19/// The algorithm used here is translated from [the `xoshiro128starstar.c`
20/// reference source code](http://xoshiro.di.unimi.it/xoshiro128starstar.c) by
21/// David Blackman and Sebastiano Vigna.
22#[derive(Debug, Clone)]
23pub struct Xoshiro128Plus {
24    s: [u32; 4],
25}
26
27impl Xoshiro128Plus {
28    /// Jump forward, equivalently to 2^64 calls to `next_u32()`.
29    ///
30    /// This can be used to generate 2^64 non-overlapping subsequences for
31    /// parallel computations.
32    ///
33    /// ```
34    /// # extern crate rand;
35    /// # extern crate rand_xoshiro;
36    /// # fn main() {
37    /// use rand::SeedableRng;
38    /// use rand_xoshiro::Xoroshiro128StarStar;
39    ///
40    /// let rng1 = Xoroshiro128StarStar::seed_from_u64(0);
41    /// let mut rng2 = rng1.clone();
42    /// rng2.jump();
43    /// let mut rng3 = rng2.clone();
44    /// rng3.jump();
45    /// # }
46    /// ```
47    pub fn jump(&mut self) {
48        impl_jump!(u32, self, [0x8764000b, 0xf542d2d3, 0x6fa035c3, 0x77f2db5b]);
49    }
50}
51
52impl SeedableRng for Xoshiro128Plus {
53    type Seed = [u8; 16];
54
55    /// Create a new `Xoshiro128Plus`.  If `seed` is entirely 0, it will be
56    /// mapped to a different seed.
57    #[inline]
58    fn from_seed(seed: [u8; 16]) -> Xoshiro128Plus {
59        deal_with_zero_seed!(seed, Self);
60        let mut state = [0; 4];
61        read_u32_into(&seed, &mut state);
62        Xoshiro128Plus { s: state }
63    }
64
65    /// Seed a `Xoshiro128Plus` from a `u64` using `SplitMix64`.
66    fn seed_from_u64(seed: u64) -> Xoshiro128Plus {
67        from_splitmix!(seed)
68    }
69}
70
71impl RngCore for Xoshiro128Plus {
72    #[inline]
73    fn next_u32(&mut self) -> u32 {
74        let result_plus = self.s[0].wrapping_add(self.s[3]);
75        impl_xoshiro_u32!(self);
76        result_plus
77    }
78
79    #[inline]
80    fn next_u64(&mut self) -> u64 {
81        next_u64_via_u32(self)
82    }
83
84    #[inline]
85    fn fill_bytes(&mut self, dest: &mut [u8]) {
86        fill_bytes_via_next(self, dest);
87    }
88
89    #[inline]
90    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
91        self.fill_bytes(dest);
92        Ok(())
93    }
94}
95
96#[cfg(test)]
97mod tests {
98    use super::*;
99
100    #[test]
101    fn reference() {
102        let mut rng = Xoshiro128Plus::from_seed(
103            [1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0]);
104        // These values were produced with the reference implementation:
105        // http://xoshiro.di.unimi.it/xoshiro128plus.c
106        let expected = [
107            5, 12295, 25178119, 27286542, 39879690, 1140358681, 3276312097,
108            4110231701, 399823256, 2144435200,
109        ];
110        for &e in &expected {
111            assert_eq!(rng.next_u32(), e);
112        }
113    }
114}
rand_xoshiro/xoshiro128plus.rs

rand_xoshiro/
xoshiro128plus.rs
