rand_xoshiro/
xoroshiro128starstar.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 xoroshiro128** random number generator.
16///
17/// The xoroshiro128** 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 `xoroshiro128starstar.c`
21/// reference source code](http://xoshiro.di.unimi.it/xoroshiro128starstar.c) by
22/// David Blackman and Sebastiano Vigna.
23#[allow(missing_copy_implementations)]
24#[derive(Debug, Clone, PartialEq, Eq)]
25#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
26pub struct Xoroshiro128StarStar {
27    s0: u64,
28    s1: u64,
29}
30
31impl Xoroshiro128StarStar {
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::Xoroshiro128StarStar;
40    ///
41    /// let rng1 = Xoroshiro128StarStar::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 Xoroshiro128StarStar {
62    #[inline]
63    fn next_u32(&mut self) -> u32 {
64        self.next_u64() as u32
65    }
66
67    #[inline]
68    fn next_u64(&mut self) -> u64 {
69        let r = starstar_u64!(self.s0);
70        impl_xoroshiro_u64!(self);
71        r
72    }
73
74    #[inline]
75    fn fill_bytes(&mut self, dest: &mut [u8]) {
76        fill_bytes_via_next(self, dest);
77    }
78}
79
80impl SeedableRng for Xoroshiro128StarStar {
81    type Seed = [u8; 16];
82
83    /// Create a new `Xoroshiro128StarStar`.  If `seed` is entirely 0, it will be
84    /// mapped to a different seed.
85    fn from_seed(seed: [u8; 16]) -> Xoroshiro128StarStar {
86        deal_with_zero_seed!(seed, Self, 16);
87        let mut s = [0; 2];
88        read_u64_into(&seed, &mut s);
89
90        Xoroshiro128StarStar { s0: s[0], s1: s[1] }
91    }
92
93    /// Seed a `Xoroshiro128StarStar` from a `u64` using `SplitMix64`.
94    fn seed_from_u64(seed: u64) -> Xoroshiro128StarStar {
95        from_splitmix!(seed)
96    }
97}
98
99#[cfg(test)]
100mod tests {
101    use super::*;
102
103    #[test]
104    fn reference() {
105        let mut rng =
106            Xoroshiro128StarStar::from_seed([1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0]);
107        // These values were produced with the reference implementation:
108        // http://xoshiro.di.unimi.it/xoshiro128starstar.c
109        let expected = [
110            5760,
111            97769243520,
112            9706862127477703552,
113            9223447511460779954,
114            8358291023205304566,
115            15695619998649302768,
116            8517900938696309774,
117            16586480348202605369,
118            6959129367028440372,
119            16822147227405758281,
120        ];
121        for &e in &expected {
122            assert_eq!(rng.next_u64(), e);
123        }
124    }
125}
rand_xoshiro/xoroshiro128starstar.rs

rand_xoshiro/
xoroshiro128starstar.rs
