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, next_u64_via_u32};
10use rand_core::le::read_u32_into;
11use rand_core::{RngCore, SeedableRng};
12#[cfg(feature = "serde")]
13use serde::{Deserialize, Serialize};
14
15/// A xoshiro128++ random number generator.
16///
17/// The xoshiro128++ 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 `xoshiro128plusplus.c`
21/// reference source code](http://xoshiro.di.unimi.it/xoshiro128plusplus.c) by
22/// David Blackman and Sebastiano Vigna.
23#[derive(Debug, Clone, PartialEq, Eq)]
24#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
25pub struct Xoshiro128PlusPlus {
26 s: [u32; 4],
27}
28
29impl Xoshiro128PlusPlus {
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::Xoroshiro128PlusPlus;
38 ///
39 /// let rng1 = Xoroshiro128PlusPlus::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 /// Jump forward, equivalently to 2^96 calls to `next_u32()`.
50 ///
51 /// This can be used to generate 2^32 starting points, from each of which
52 /// `jump()` will generate 2^32 non-overlapping subsequences for parallel
53 /// distributed computations.
54 pub fn long_jump(&mut self) {
55 impl_jump!(u32, self, [0xb523952e, 0x0b6f099f, 0xccf5a0ef, 0x1c580662]);
56 }
57}
58
59impl SeedableRng for Xoshiro128PlusPlus {
60 type Seed = [u8; 16];
61
62 /// Create a new `Xoshiro128PlusPlus`. If `seed` is entirely 0, it will be
63 /// mapped to a different seed.
64 #[inline]
65 fn from_seed(seed: [u8; 16]) -> Xoshiro128PlusPlus {
66 deal_with_zero_seed!(seed, Self, 16);
67 let mut state: [u32; 4] = [0; 4];
68 read_u32_into(&seed, &mut state);
69 Xoshiro128PlusPlus { s: state }
70 }
71
72 /// Seed a `Xoshiro128PlusPlus` from a `u64` using `SplitMix64`.
73 fn seed_from_u64(seed: u64) -> Xoshiro128PlusPlus {
74 from_splitmix!(seed)
75 }
76}
77
78impl RngCore for Xoshiro128PlusPlus {
79 #[inline]
80 fn next_u32(&mut self) -> u32 {
81 let result_starstar: u32 = plusplus_u32!(self.s[0], self.s[3]);
82 impl_xoshiro_u32!(self);
83 result_starstar
84 }
85
86 #[inline]
87 fn next_u64(&mut self) -> u64 {
88 next_u64_via_u32(self)
89 }
90
91 #[inline]
92 fn fill_bytes(&mut self, dest: &mut [u8]) {
93 fill_bytes_via_next(self, dest);
94 }
95}
96
97#[cfg(test)]
98mod tests {
99 use super::*;
100
101 #[test]
102 fn reference() {
103 let mut rng =
104 Xoshiro128PlusPlus::from_seed([1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0]);
105 // These values were produced with the reference implementation:
106 // http://xoshiro.di.unimi.it/xoshiro128plusplus.c
107 let expected = [
108 641, 1573767, 3222811527, 3517856514, 836907274, 4247214768, 3867114732, 1355841295,
109 495546011, 621204420,
110 ];
111 for &e in &expected {
112 assert_eq!(rng.next_u32(), e);
113 }
114 }
115
116 #[test]
117 fn test_jump() {
118 let mut rng =
119 Xoshiro128PlusPlus::from_seed([1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0]);
120 rng.jump();
121 // These values were produced by instrumenting the reference implementation:
122 // http://xoshiro.di.unimi.it/xoshiro128plus.c
123 assert_eq!(rng.s[0], 2843103750);
124 assert_eq!(rng.s[1], 2038079848);
125 assert_eq!(rng.s[2], 1533207345);
126 assert_eq!(rng.s[3], 44816753);
127 }
128
129 #[test]
130 fn test_long_jump() {
131 let mut rng =
132 Xoshiro128PlusPlus::from_seed([1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0]);
133 rng.long_jump();
134 // These values were produced by instrumenting the reference implementation:
135 // http://xoshiro.di.unimi.it/xoshiro128plus.c
136 assert_eq!(rng.s[0], 1611968294);
137 assert_eq!(rng.s[1], 2125834322);
138 assert_eq!(rng.s[2], 966769569);
139 assert_eq!(rng.s[3], 3193880526);
140 }
141}
142