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
15use crate::Seed512;
16
17/// A xoshiro512** random number generator.
18///
19/// The xoshiro512** algorithm is not suitable for cryptographic purposes, but
20/// is very fast and has excellent statistical properties.
21///
22/// The algorithm used here is translated from [the `xoshiro512starstar.c`
23/// reference source code](http://xoshiro.di.unimi.it/xoshiro512starstar.c) by
24/// David Blackman and Sebastiano Vigna.
25#[derive(Debug, Clone, PartialEq, Eq)]
26#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
27pub struct Xoshiro512StarStar {
28 s: [u64; 8],
29}
30
31impl Xoshiro512StarStar {
32 /// Jump forward, equivalently to 2^256 calls to `next_u64()`.
33 ///
34 /// This can be used to generate 2^256 non-overlapping subsequences for
35 /// parallel computations.
36 ///
37 /// ```
38 /// use rand_xoshiro::rand_core::SeedableRng;
39 /// use rand_xoshiro::Xoshiro512StarStar;
40 ///
41 /// let rng1 = Xoshiro512StarStar::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!(
49 u64,
50 self,
51 [
52 0x33ed89b6e7a353f9,
53 0x760083d7955323be,
54 0x2837f2fbb5f22fae,
55 0x4b8c5674d309511c,
56 0xb11ac47a7ba28c25,
57 0xf1be7667092bcc1c,
58 0x53851efdb6df0aaf,
59 0x1ebbc8b23eaf25db
60 ]
61 );
62 }
63
64 /// Jump forward, equivalently to 2^384 calls to `next_u64()`.
65 ///
66 /// This can be used to generate 2^128 starting points, from each of which
67 /// `jump()` will generate 2^128 non-overlapping subsequences for parallel
68 /// distributed computations.
69 pub fn long_jump(&mut self) {
70 impl_jump!(
71 u64,
72 self,
73 [
74 0x11467fef8f921d28,
75 0xa2a819f2e79c8ea8,
76 0xa8299fc284b3959a,
77 0xb4d347340ca63ee1,
78 0x1cb0940bedbff6ce,
79 0xd956c5c4fa1f8e17,
80 0x915e38fd4eda93bc,
81 0x5b3ccdfa5d7daca5
82 ]
83 );
84 }
85}
86
87impl SeedableRng for Xoshiro512StarStar {
88 type Seed = Seed512;
89
90 /// Create a new `Xoshiro512StarStar`. If `seed` is entirely 0, it will be
91 /// mapped to a different seed.
92 #[inline]
93 fn from_seed(seed: Seed512) -> Xoshiro512StarStar {
94 deal_with_zero_seed!(seed, Self);
95 let mut state: [u64; 8] = [0; 8];
96 read_u64_into(&seed.0, &mut state);
97 Xoshiro512StarStar { s: state }
98 }
99
100 /// Seed a `Xoshiro512StarStar` from a `u64` using `SplitMix64`.
101 fn seed_from_u64(seed: u64) -> Xoshiro512StarStar {
102 from_splitmix!(seed)
103 }
104}
105
106impl RngCore for Xoshiro512StarStar {
107 #[inline]
108 fn next_u32(&mut self) -> u32 {
109 // The lowest bits have some linear dependencies, so we use the
110 // upper bits instead.
111 (self.next_u64() >> 32) as u32
112 }
113
114 #[inline]
115 fn next_u64(&mut self) -> u64 {
116 let result_starstar: u64 = starstar_u64!(self.s[1]);
117 impl_xoshiro_large!(self);
118 result_starstar
119 }
120
121 #[inline]
122 fn fill_bytes(&mut self, dest: &mut [u8]) {
123 fill_bytes_via_next(self, dest);
124 }
125}
126
127#[cfg(test)]
128mod tests {
129 use super::*;
130
131 #[test]
132 #[rustfmt::skip]
133 fn reference() {
134 let mut rng = Xoshiro512StarStar::from_seed(Seed512(
135 [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0,
136 3, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0,
137 5, 0, 0, 0, 0, 0, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0,
138 7, 0, 0, 0, 0, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0]));
139 // These values were produced with the reference implementation:
140 // http://xoshiro.di.unimi.it/xoshiro512starstar.c
141 let expected = [
142 11520,
143 0,
144 23040,
145 23667840,
146 144955163520,
147 303992986974289920,
148 25332796375735680,
149 296904390158016,
150 13911081092387501979,
151 15304787717237593024,
152 ];
153 for &e in &expected {
154 assert_eq!(rng.next_u64(), e);
155 }
156 }
157}
158