rand_xoshiro/
xoroshiro128starstar.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
9#[cfg(feature="serde1")] use serde::{Serialize, Deserialize};
10use rand_core::le::read_u64_into;
11use rand_core::impls::fill_bytes_via_next;
12use rand_core::{RngCore, SeedableRng};
13
14/// A xoroshiro128** random number generator.
15///
16/// The xoroshiro128** algorithm is not suitable for cryptographic purposes, but
17/// is very fast and has excellent statistical properties.
18///
19/// The algorithm used here is translated from [the `xoroshiro128starstar.c`
20/// reference source code](http://xoshiro.di.unimi.it/xoroshiro128starstar.c) by
21/// David Blackman and Sebastiano Vigna.
22#[allow(missing_copy_implementations)]
23#[derive(Debug, Clone, PartialEq, Eq)]
24#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
25pub struct Xoroshiro128StarStar {
26    s0: u64,
27    s1: u64,
28}
29
30impl Xoroshiro128StarStar {
31    /// Jump forward, equivalently to 2^64 calls to `next_u64()`.
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!(u64, self, [0xdf900294d8f554a5, 0x170865df4b3201fc]);
48    }
49
50    /// Jump forward, equivalently to 2^96 calls to `next_u64()`.
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!(u64, self, [0xd2a98b26625eee7b, 0xdddf9b1090aa7ac1]);
57    }
58}
59
60impl RngCore for Xoroshiro128StarStar {
61    #[inline]
62    fn next_u32(&mut self) -> u32 {
63        self.next_u64() as u32
64    }
65
66    #[inline]
67    fn next_u64(&mut self) -> u64 {
68        let r = starstar_u64!(self.s0);
69        impl_xoroshiro_u64!(self);
70        r
71    }
72
73    #[inline]
74    fn fill_bytes(&mut self, dest: &mut [u8]) {
75        fill_bytes_via_next(self, dest);
76    }
77
78    #[inline]
79    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand_core::Error> {
80        self.fill_bytes(dest);
81        Ok(())
82    }
83}
84
85impl SeedableRng for Xoroshiro128StarStar {
86    type Seed = [u8; 16];
87
88    /// Create a new `Xoroshiro128StarStar`.  If `seed` is entirely 0, it will be
89    /// mapped to a different seed.
90    fn from_seed(seed: [u8; 16]) -> Xoroshiro128StarStar {
91        deal_with_zero_seed!(seed, Self);
92        let mut s = [0; 2];
93        read_u64_into(&seed, &mut s);
94
95        Xoroshiro128StarStar {
96            s0: s[0],
97            s1: s[1],
98        }
99    }
100
101    /// Seed a `Xoroshiro128StarStar` from a `u64` using `SplitMix64`.
102    fn seed_from_u64(seed: u64) -> Xoroshiro128StarStar {
103        from_splitmix!(seed)
104    }
105}
106
107#[cfg(test)]
108mod tests {
109    use super::*;
110
111    #[test]
112    fn reference() {
113        let mut rng = Xoroshiro128StarStar::from_seed(
114            [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0]);
115        // These values were produced with the reference implementation:
116        // http://xoshiro.di.unimi.it/xoshiro128starstar.c
117        let expected = [
118            5760, 97769243520, 9706862127477703552, 9223447511460779954,
119            8358291023205304566, 15695619998649302768, 8517900938696309774,
120            16586480348202605369, 6959129367028440372, 16822147227405758281,
121        ];
122        for &e in &expected {
123            assert_eq!(rng.next_u64(), e);
124        }
125    }
126}
rand_xoshiro/xoroshiro128starstar.rs

rand_xoshiro/
xoroshiro128starstar.rs
