rand_xoshiro/
xoshiro128starstar.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 excellent statistical properties.
19///
20/// The algorithm used here is translated from [the `xoshiro128starstar.c`
21/// reference source code](http://xoshiro.di.unimi.it/xoshiro128starstar.c) by
22/// David Blackman and Sebastiano Vigna.
23#[derive(Debug, Clone, PartialEq, Eq)]
24#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
25pub struct Xoshiro128StarStar {
26    s: [u32; 4],
27}
28
29impl Xoshiro128StarStar {
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::Xoroshiro128StarStar;
38    ///
39    /// let rng1 = Xoroshiro128StarStar::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 Xoshiro128StarStar {
60    type Seed = [u8; 16];
61
62    /// Create a new `Xoshiro128StarStar`.  If `seed` is entirely 0, it will be
63    /// mapped to a different seed.
64    #[inline]
65    fn from_seed(seed: [u8; 16]) -> Xoshiro128StarStar {
66        deal_with_zero_seed!(seed, Self, 16);
67        let mut state = [0; 4];
68        read_u32_into(&seed, &mut state);
69        Xoshiro128StarStar { s: state }
70    }
71
72    /// Seed a `Xoshiro128StarStar` from a `u64` using `SplitMix64`.
73    fn seed_from_u64(seed: u64) -> Xoshiro128StarStar {
74        from_splitmix!(seed)
75    }
76}
77
78impl RngCore for Xoshiro128StarStar {
79    #[inline]
80    fn next_u32(&mut self) -> u32 {
81        let result_starstar = starstar_u64!(self.s[1]);
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            Xoshiro128StarStar::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 (v1.1):
106        // http://xoshiro.di.unimi.it/xoshiro128starstar.c
107        let expected = [
108            11520, 0, 5927040, 70819200, 2031721883, 1637235492, 1287239034, 3734860849,
109            3729100597, 4258142804,
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            Xoshiro128StarStar::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            Xoshiro128StarStar::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}
rand_xoshiro/xoshiro128starstar.rs

rand_xoshiro/
xoshiro128starstar.rs
