rand_xoshiro/
xoshiro512starstar.rs

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 core::convert::Infallible;
10use rand_core::{Rng, SeedableRng, TryRng, utils};
11#[cfg(feature = "serde")]
12use serde::{Deserialize, Serialize};
13
14use crate::Seed512;
15
16/// A xoshiro512** random number generator.
17///
18/// The xoshiro512** algorithm is not suitable for cryptographic purposes, but
19/// is very fast and has excellent statistical properties.
20///
21/// The algorithm used here is translated from [the `xoshiro512starstar.c`
22/// reference source code](http://xoshiro.di.unimi.it/xoshiro512starstar.c) by
23/// David Blackman and Sebastiano Vigna.
24#[derive(Debug, Clone, PartialEq, Eq)]
25#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
26pub struct Xoshiro512StarStar {
27    s: [u64; 8],
28}
29
30impl Xoshiro512StarStar {
31    /// Jump forward, equivalently to 2^256 calls to `next_u64()`.
32    ///
33    /// This can be used to generate 2^256 non-overlapping subsequences for
34    /// parallel computations.
35    ///
36    /// ```
37    /// use rand_xoshiro::rand_core::SeedableRng;
38    /// use rand_xoshiro::Xoshiro512StarStar;
39    ///
40    /// let rng1 = Xoshiro512StarStar::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!(
48            u64,
49            self,
50            [
51                0x33ed89b6e7a353f9,
52                0x760083d7955323be,
53                0x2837f2fbb5f22fae,
54                0x4b8c5674d309511c,
55                0xb11ac47a7ba28c25,
56                0xf1be7667092bcc1c,
57                0x53851efdb6df0aaf,
58                0x1ebbc8b23eaf25db
59            ]
60        );
61    }
62
63    /// Jump forward, equivalently to 2^384 calls to `next_u64()`.
64    ///
65    /// This can be used to generate 2^128 starting points, from each of which
66    /// `jump()` will generate 2^128 non-overlapping subsequences for parallel
67    /// distributed computations.
68    pub fn long_jump(&mut self) {
69        impl_jump!(
70            u64,
71            self,
72            [
73                0x11467fef8f921d28,
74                0xa2a819f2e79c8ea8,
75                0xa8299fc284b3959a,
76                0xb4d347340ca63ee1,
77                0x1cb0940bedbff6ce,
78                0xd956c5c4fa1f8e17,
79                0x915e38fd4eda93bc,
80                0x5b3ccdfa5d7daca5
81            ]
82        );
83    }
84}
85
86impl_state_seed512!(Xoshiro512StarStar);
87
88impl SeedableRng for Xoshiro512StarStar {
89    type Seed = Seed512;
90
91    /// Create a new `Xoshiro512StarStar`.  If `seed` is entirely 0, it will be
92    /// mapped to a different seed.
93    #[inline]
94    fn from_seed(seed: Seed512) -> Xoshiro512StarStar {
95        Xoshiro512StarStar {
96            s: utils::read_words(crate::common::zero_seed_fallback(&seed.0)),
97        }
98    }
99
100    /// Seed a `Xoshiro512StarStar` from a `u64` using `SplitMix64`.
101    fn seed_from_u64(seed: u64) -> Xoshiro512StarStar {
102        from_splitmix!(seed)
103    }
104}
105
106impl TryRng for Xoshiro512StarStar {
107    type Error = Infallible;
108
109    #[inline]
110    fn try_next_u32(&mut self) -> Result<u32, Self::Error> {
111        // The lowest bits have some linear dependencies, so we use the
112        // upper bits instead.
113        Ok((self.next_u64() >> 32) as u32)
114    }
115
116    #[inline]
117    fn try_next_u64(&mut self) -> Result<u64, Self::Error> {
118        let result_starstar = starstar_u64!(self.s[1]);
119        impl_xoshiro_large!(self);
120        Ok(result_starstar)
121    }
122
123    #[inline]
124    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Self::Error> {
125        utils::fill_bytes_via_next_word(dest, || self.try_next_u64())
126    }
127}
128
129#[cfg(test)]
130mod tests {
131    use super::*;
132
133    #[test]
134    #[rustfmt::skip]
135    fn reference() {
136        let mut rng = Xoshiro512StarStar::from_seed(Seed512(
137            [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0,
138             3, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0,
139             5, 0, 0, 0, 0, 0, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0,
140             7, 0, 0, 0, 0, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0]));
141        // These values were produced with the reference implementation:
142        // http://xoshiro.di.unimi.it/xoshiro512starstar.c
143        let expected = [
144            11520,
145            0,
146            23040,
147            23667840,
148            144955163520,
149            303992986974289920,
150            25332796375735680,
151            296904390158016,
152            13911081092387501979,
153            15304787717237593024,
154        ];
155        for &e in &expected {
156            assert_eq!(rng.next_u64(), e);
157        }
158    }
159
160    #[test]
161    fn zero_seed_maps_to_seed_from_u64_zero() {
162        let from_zero = Xoshiro512StarStar::from_seed(Seed512([0u8; 64]));
163        let from_sm0 = Xoshiro512StarStar::seed_from_u64(0);
164        assert_eq!(from_zero, from_sm0);
165    }
166
167    #[test]
168    fn state_roundtrip() {
169        let rng = Xoshiro512StarStar::seed_from_u64(42);
170        let clone = Xoshiro512StarStar::from_seed(rng.state());
171        assert_eq!(clone, rng);
172    }
173}
rand_xoshiro/xoshiro512starstar.rs

rand_xoshiro/
xoshiro512starstar.rs
