rand_xoshiro/
xoshiro128plus.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::{next_u64_via_u32, fill_bytes_via_next};
11use rand_core::le::read_u32_into;
12use rand_core::{SeedableRng, RngCore, Error};
13
14/// A xoshiro128+ random number generator.
15///
16/// The xoshiro128+ 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 `xoshiro128starstar.c`
21/// reference source code](http://xoshiro.di.unimi.it/xoshiro128starstar.c) by
22/// David Blackman and Sebastiano Vigna.
23#[derive(Debug, Clone, PartialEq, Eq)]
24#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
25pub struct Xoshiro128Plus {
26    s: [u32; 4],
27}
28
29impl Xoshiro128Plus {
30    /// Jump forward, equivalently to 2^64 calls to `next_u32()`.
31    ///
32    /// This can be used to generate 2^64 non-overlapping subsequences for
33    /// parallel computations.
34    ///
35    /// ```
36    /// use rand_xoshiro::rand_core::SeedableRng;
37    /// use rand_xoshiro::Xoroshiro128StarStar;
38    ///
39    /// let rng1 = Xoroshiro128StarStar::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!(u32, self, [0x8764000b, 0xf542d2d3, 0x6fa035c3, 0x77f2db5b]);
47    }
48}
49
50impl SeedableRng for Xoshiro128Plus {
51    type Seed = [u8; 16];
52
53    /// Create a new `Xoshiro128Plus`.  If `seed` is entirely 0, it will be
54    /// mapped to a different seed.
55    #[inline]
56    fn from_seed(seed: [u8; 16]) -> Xoshiro128Plus {
57        deal_with_zero_seed!(seed, Self);
58        let mut state = [0; 4];
59        read_u32_into(&seed, &mut state);
60        Xoshiro128Plus { s: state }
61    }
62
63    /// Seed a `Xoshiro128Plus` from a `u64` using `SplitMix64`.
64    fn seed_from_u64(seed: u64) -> Xoshiro128Plus {
65        from_splitmix!(seed)
66    }
67}
68
69impl RngCore for Xoshiro128Plus {
70    #[inline]
71    fn next_u32(&mut self) -> u32 {
72        let result_plus = self.s[0].wrapping_add(self.s[3]);
73        impl_xoshiro_u32!(self);
74        result_plus
75    }
76
77    #[inline]
78    fn next_u64(&mut self) -> u64 {
79        next_u64_via_u32(self)
80    }
81
82    #[inline]
83    fn fill_bytes(&mut self, dest: &mut [u8]) {
84        fill_bytes_via_next(self, dest);
85    }
86
87    #[inline]
88    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
89        self.fill_bytes(dest);
90        Ok(())
91    }
92}
93
94#[cfg(test)]
95mod tests {
96    use super::*;
97
98    #[test]
99    fn reference() {
100        let mut rng = Xoshiro128Plus::from_seed(
101            [1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0]);
102        // These values were produced with the reference implementation:
103        // http://xoshiro.di.unimi.it/xoshiro128plus.c
104        let expected = [
105            5, 12295, 25178119, 27286542, 39879690, 1140358681, 3276312097,
106            4110231701, 399823256, 2144435200,
107        ];
108        for &e in &expected {
109            assert_eq!(rng.next_u32(), e);
110        }
111    }
112}
rand_xoshiro/xoshiro128plus.rs

rand_xoshiro/
xoshiro128plus.rs
