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 good statistical properties, besides a low linear
19/// complexity in the lowest bits.
20///
21/// The algorithm used here is translated from [the `xoshiro128starstar.c`
22/// reference source code](http://xoshiro.di.unimi.it/xoshiro128starstar.c) by
23/// David Blackman and Sebastiano Vigna.
24#[derive(Debug, Clone, PartialEq, Eq)]
25#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
26pub struct Xoshiro128Plus {
27 s: [u32; 4],
28}
29
30impl Xoshiro128Plus {
31 /// Jump forward, equivalently to 2^64 calls to `next_u32()`.
32 ///
33 /// This can be used to generate 2^64 non-overlapping subsequences for
34 /// parallel computations.
35 ///
36 /// ```
37 /// use rand_xoshiro::rand_core::SeedableRng;
38 /// use rand_xoshiro::Xoroshiro128StarStar;
39 ///
40 /// let rng1 = Xoroshiro128StarStar::seed_from_u64(0);
41 /// let mut rng2 = rng1.clone();
42 /// rng2.jump();
43 /// let mut rng3 = rng2.clone();
44 /// rng3.jump();
45 /// ```
46 pub fn jump(&mut self) {
47 impl_jump!(u32, self, [0x8764000b, 0xf542d2d3, 0x6fa035c3, 0x77f2db5b]);
48 }
49
50 /// Jump forward, equivalently to 2^96 calls to `next_u32()`.
51 ///
52 /// This can be used to generate 2^32 starting points, from each of which
53 /// `jump()` will generate 2^32 non-overlapping subsequences for parallel
54 /// distributed computations.
55 pub fn long_jump(&mut self) {
56 impl_jump!(u32, self, [0xb523952e, 0x0b6f099f, 0xccf5a0ef, 0x1c580662]);
57 }
58}
59
60impl SeedableRng for Xoshiro128Plus {
61 type Seed = [u8; 16];
62
63 /// Create a new `Xoshiro128Plus`. If `seed` is entirely 0, it will be
64 /// mapped to a different seed.
65 #[inline]
66 fn from_seed(seed: [u8; 16]) -> Xoshiro128Plus {
67 deal_with_zero_seed!(seed, Self, 16);
68 let mut state: [u32; 4] = [0; 4];
69 read_u32_into(&seed, &mut state);
70 Xoshiro128Plus { s: state }
71 }
72
73 /// Seed a `Xoshiro128Plus` from a `u64` using `SplitMix64`.
74 fn seed_from_u64(seed: u64) -> Xoshiro128Plus {
75 from_splitmix!(seed)
76 }
77}
78
79impl RngCore for Xoshiro128Plus {
80 #[inline]
81 fn next_u32(&mut self) -> u32 {
82 let result_plus: u32 = self.s[0].wrapping_add(self.s[3]);
83 impl_xoshiro_u32!(self);
84 result_plus
85 }
86
87 #[inline]
88 fn next_u64(&mut self) -> u64 {
89 next_u64_via_u32(self)
90 }
91
92 #[inline]
93 fn fill_bytes(&mut self, dest: &mut [u8]) {
94 fill_bytes_via_next(self, dest);
95 }
96}
97
98#[cfg(test)]
99mod tests {
100 use super::*;
101
102 #[test]
103 fn reference() {
104 let mut rng = Xoshiro128Plus::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/xoshiro128plus.c
107 let expected = [
108 5, 12295, 25178119, 27286542, 39879690, 1140358681, 3276312097, 4110231701, 399823256,
109 2144435200,
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 = Xoshiro128Plus::from_seed([1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0]);
119 rng.jump();
120 // These values were produced by instrumenting the reference implementation:
121 // http://xoshiro.di.unimi.it/xoshiro128plus.c
122 assert_eq!(rng.s[0], 2843103750);
123 assert_eq!(rng.s[1], 2038079848);
124 assert_eq!(rng.s[2], 1533207345);
125 assert_eq!(rng.s[3], 44816753);
126 }
127
128 #[test]
129 fn test_long_jump() {
130 let mut rng = Xoshiro128Plus::from_seed([1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0]);
131 rng.long_jump();
132 // These values were produced by instrumenting the reference implementation:
133 // http://xoshiro.di.unimi.it/xoshiro128plus.c
134 assert_eq!(rng.s[0], 1611968294);
135 assert_eq!(rng.s[1], 2125834322);
136 assert_eq!(rng.s[2], 966769569);
137 assert_eq!(rng.s[3], 3193880526);
138 }
139}
140