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 `xoroshiro128plusplus.c`
21/// reference source code](http://xoshiro.di.unimi.it/xoroshiro128plusplus.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 Xoroshiro128PlusPlus {
27 s0: u64,
28 s1: u64,
29}
30
31impl Xoroshiro128PlusPlus {
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::Xoroshiro128PlusPlus;
40 ///
41 /// let rng1 = Xoroshiro128PlusPlus::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, [0x2bd7a6a6e99c2ddc, 0x0992ccaf6a6fca05]);
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, [0x360fd5f2cf8d5d99, 0x9c6e6877736c46e3]);
58 }
59}
60
61impl RngCore for Xoroshiro128PlusPlus {
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: u64 = plusplus_u64!(self.s0, self.s1, 17);
70 impl_xoroshiro_u64_plusplus!(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 Xoroshiro128PlusPlus {
81 type Seed = [u8; 16];
82
83 /// Create a new `Xoroshiro128PlusPlus`. If `seed` is entirely 0, it will be
84 /// mapped to a different seed.
85 fn from_seed(seed: [u8; 16]) -> Xoroshiro128PlusPlus {
86 deal_with_zero_seed!(seed, Self, 16);
87 let mut s: [u64; 2] = [0; 2];
88 read_u64_into(&seed, &mut s);
89
90 Xoroshiro128PlusPlus { s0: s[0], s1: s[1] }
91 }
92
93 /// Seed a `Xoroshiro128PlusPlus` from a `u64` using `SplitMix64`.
94 fn seed_from_u64(seed: u64) -> Xoroshiro128PlusPlus {
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 Xoroshiro128PlusPlus::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/xoshiro128plusplus.c
109 let expected = [
110 393217,
111 669327710093319,
112 1732421326133921491,
113 11394790081659126983,
114 9555452776773192676,
115 3586421180005889563,
116 1691397964866707553,
117 10735626796753111697,
118 15216282715349408991,
119 14247243556711267923,
120 ];
121 for &e in &expected {
122 assert_eq!(rng.next_u64(), e);
123 }
124 }
125}
126

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