rand_xoshiro/
xoshiro128plus.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, 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 = [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 = 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}
rand_xoshiro/xoshiro128plus.rs

rand_xoshiro/
xoshiro128plus.rs
