rand_xoshiro/
xoshiro256plus.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::impls::fill_bytes_via_next;
11use rand_core::le::read_u64_into;
12use rand_core::{SeedableRng, RngCore, Error};
13
14/// A xoshiro256+ random number generator.
15///
16/// The xoshiro256+ algorithm is not suitable for cryptographic purposes, but
17/// is very fast and has good statistical properties, besides a low linear
18/// complexity in the lowest bits.
19///
20/// The algorithm used here is translated from [the `xoshiro256plus.c`
21/// reference source code](http://xoshiro.di.unimi.it/xoshiro256plus.c) by
22/// David Blackman and Sebastiano Vigna.
23#[derive(Debug, Clone, PartialEq, Eq)]
24#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
25pub struct Xoshiro256Plus {
26    s: [u64; 4],
27}
28
29impl Xoshiro256Plus {
30    /// Jump forward, equivalently to 2^128 calls to `next_u64()`.
31    ///
32    /// This can be used to generate 2^128 non-overlapping subsequences for
33    /// parallel computations.
34    ///
35    /// ```
36    /// use rand_xoshiro::rand_core::SeedableRng;
37    /// use rand_xoshiro::Xoshiro256Plus;
38    ///
39    /// let rng1 = Xoshiro256Plus::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!(u64, self, [
47            0x180ec6d33cfd0aba, 0xd5a61266f0c9392c,
48            0xa9582618e03fc9aa, 0x39abdc4529b1661c
49        ]);
50    }
51
52    /// Jump forward, equivalently to 2^192 calls to `next_u64()`.
53    ///
54    /// This can be used to generate 2^64 starting points, from each of which
55    /// `jump()` will generate 2^64 non-overlapping subsequences for parallel
56    /// distributed computations.
57    pub fn long_jump(&mut self) {
58        impl_jump!(u64, self, [
59            0x76e15d3efefdcbbf, 0xc5004e441c522fb3,
60            0x77710069854ee241, 0x39109bb02acbe635
61        ]);
62    }
63}
64
65impl SeedableRng for Xoshiro256Plus {
66    type Seed = [u8; 32];
67
68    /// Create a new `Xoshiro256Plus`.  If `seed` is entirely 0, it will be
69    /// mapped to a different seed.
70    #[inline]
71    fn from_seed(seed: [u8; 32]) -> Xoshiro256Plus {
72        deal_with_zero_seed!(seed, Self);
73        let mut state = [0; 4];
74        read_u64_into(&seed, &mut state);
75        Xoshiro256Plus { s: state }
76    }
77
78    /// Seed a `Xoshiro256Plus` from a `u64` using `SplitMix64`.
79    fn seed_from_u64(seed: u64) -> Xoshiro256Plus {
80        from_splitmix!(seed)
81    }
82}
83
84impl RngCore for Xoshiro256Plus {
85    #[inline]
86    fn next_u32(&mut self) -> u32 {
87        // The lowest bits have some linear dependencies, so we use the
88        // upper bits instead.
89        (self.next_u64() >> 32) as u32
90    }
91
92    #[inline]
93    fn next_u64(&mut self) -> u64 {
94        let result_plus = self.s[0].wrapping_add(self.s[3]);
95        impl_xoshiro_u64!(self);
96        result_plus
97    }
98
99    #[inline]
100    fn fill_bytes(&mut self, dest: &mut [u8]) {
101        fill_bytes_via_next(self, dest);
102    }
103
104    #[inline]
105    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
106        self.fill_bytes(dest);
107        Ok(())
108    }
109}
110
111#[cfg(test)]
112mod tests {
113    use super::*;
114
115    #[test]
116    fn reference() {
117        let mut rng = Xoshiro256Plus::from_seed(
118            [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0,
119             3, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0]);
120        // These values were produced with the reference implementation:
121        // http://xoshiro.di.unimi.it/xoshiro256plus.c
122        let expected = [
123            5, 211106232532999, 211106635186183, 9223759065350669058,
124            9250833439874351877, 13862484359527728515, 2346507365006083650,
125            1168864526675804870, 34095955243042024, 3466914240207415127,
126        ];
127        for &e in &expected {
128            assert_eq!(rng.next_u64(), e);
129        }
130    }
131}
rand_xoshiro/xoshiro256plus.rs

rand_xoshiro/
xoshiro256plus.rs
