rand_xoshiro/
splitmix64.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, Error};
13
14/// A splitmix64 random number generator.
15///
16/// The splitmix algorithm is not suitable for cryptographic purposes, but is
17/// very fast and has a 64 bit state.
18///
19/// The algorithm used here is translated from [the `splitmix64.c`
20/// reference source code](http://xoshiro.di.unimi.it/splitmix64.c) by
21/// Sebastiano Vigna. For `next_u32`, a more efficient mixing function taken
22/// from [`dsiutils`](http://dsiutils.di.unimi.it/) is used.
23#[allow(missing_copy_implementations)]
24#[derive(Debug, Clone, PartialEq, Eq)]
25#[cfg_attr(feature="serde1", derive(Serialize, Deserialize))]
26pub struct SplitMix64 {
27    x: u64,
28}
29
30const PHI: u64 = 0x9e3779b97f4a7c15;
31
32impl RngCore for SplitMix64 {
33    #[inline]
34    fn next_u32(&mut self) -> u32 {
35        self.x = self.x.wrapping_add(PHI);
36        let mut z = self.x;
37        // David Stafford's
38        // (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html)
39        // "Mix4" variant of the 64-bit finalizer in Austin Appleby's
40        // MurmurHash3 algorithm.
41        z = (z ^ (z >> 33)).wrapping_mul(0x62A9D9ED799705F5);
42        z = (z ^ (z >> 28)).wrapping_mul(0xCB24D0A5C88C35B3);
43        (z >> 32) as u32
44    }
45
46    #[inline]
47    fn next_u64(&mut self) -> u64 {
48        self.x = self.x.wrapping_add(PHI);
49        let mut z = self.x;
50        z = (z ^ (z >> 30)).wrapping_mul(0xbf58476d1ce4e5b9);
51        z = (z ^ (z >> 27)).wrapping_mul(0x94d049bb133111eb);
52        z ^ (z >> 31)
53    }
54
55    #[inline]
56    fn fill_bytes(&mut self, dest: &mut [u8]) {
57        fill_bytes_via_next(self, dest);
58    }
59
60    #[inline]
61    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
62        self.fill_bytes(dest);
63        Ok(())
64    }
65}
66
67impl SeedableRng for SplitMix64 {
68    type Seed = [u8; 8];
69
70    /// Create a new `SplitMix64`.
71    fn from_seed(seed: [u8; 8]) -> SplitMix64 {
72        let mut state = [0; 1];
73        read_u64_into(&seed, &mut state);
74        SplitMix64 {
75            x: state[0],
76        }
77    }
78
79    /// Seed a `SplitMix64` from a `u64`.
80    fn seed_from_u64(seed: u64) -> SplitMix64 {
81        SplitMix64::from_seed(seed.to_le_bytes())
82    }
83}
84
85#[cfg(test)]
86mod tests {
87    use super::*;
88
89    #[test]
90    fn reference() {
91        let mut rng = SplitMix64::seed_from_u64(1477776061723855037);
92        // These values were produced with the reference implementation:
93        // http://xoshiro.di.unimi.it/splitmix64.c
94        let expected : [u64 ; 50]= [
95            1985237415132408290, 2979275885539914483, 13511426838097143398,
96            8488337342461049707, 15141737807933549159, 17093170987380407015,
97            16389528042912955399, 13177319091862933652, 10841969400225389492,
98            17094824097954834098, 3336622647361835228, 9678412372263018368,
99            11111587619974030187, 7882215801036322410, 5709234165213761869,
100            7799681907651786826, 4616320717312661886, 4251077652075509767,
101            7836757050122171900, 5054003328188417616, 12919285918354108358,
102            16477564761813870717, 5124667218451240549, 18099554314556827626,
103            7603784838804469118, 6358551455431362471, 3037176434532249502,
104            3217550417701719149, 9958699920490216947, 5965803675992506258,
105            12000828378049868312, 12720568162811471118, 245696019213873792,
106            8351371993958923852, 14378754021282935786, 5655432093647472106,
107            5508031680350692005, 8515198786865082103, 6287793597487164412,
108            14963046237722101617, 3630795823534910476, 8422285279403485710,
109            10554287778700714153, 10871906555720704584, 8659066966120258468,
110            9420238805069527062, 10338115333623340156, 13514802760105037173,
111            14635952304031724449, 15419692541594102413,
112        ];
113        for &e in expected.iter() {
114            assert_eq!(rng.next_u64(), e);
115        }
116    }
117
118    #[test]
119    fn next_u32() {
120        let mut rng = SplitMix64::seed_from_u64(10);
121        // These values were produced with the reference implementation:
122        // http://dsiutils.di.unimi.it/dsiutils-2.5.1-src.tar.gz
123        let expected : [u32 ; 100]= [
124            3930361779, 4016923089, 4113052479, 925926767, 1755287528,
125            802865554, 954171070, 3724185978, 173676273, 1414488795, 12664133,
126            1784889697, 1303817078, 261610523, 941280008, 2571813643,
127            2954453492, 378291111, 2546873158, 3923319175, 645257028,
128            3881821278, 2681538690, 3037029984, 1999958137, 1853970361,
129            2989951788, 2126166628, 839962987, 3989679659, 3656977858,
130            684284364, 1673258011, 170979192, 3037622326, 1600748179,
131            1780764218, 1141430714, 4139736875, 3336905707, 2262051600,
132            3830850262, 2430765325, 1073032139, 1668888979, 2716938970,
133            4102420032, 40305196, 386350562, 2754480591, 622869439, 2129598760,
134            2306038241, 4218338739, 412298926, 3453855056, 3061469690,
135            4284292697, 994843708, 1591016681, 414726151, 1238182607, 18073498,
136            1237631493, 351884714, 2347486264, 2488990876, 802846256, 645670443,
137            957607012, 3126589776, 1966356370, 3036485766, 868696717,
138            2808613630, 2070968151, 1025536863, 1743949425, 466212687,
139            2994327271, 209776458, 1246125124, 3344380309, 2203947859,
140            968313105, 2805485302, 197484837, 3472483632, 3931823935,
141            3288490351, 4165666529, 3671080416, 689542830, 1272555356,
142            1039141475, 3984640460, 4142959054, 2252788890, 2459379590,
143            991872507,
144        ];
145        for &e in expected.iter() {
146            assert_eq!(rng.next_u32(), e);
147        }
148    }
149}
rand_xoshiro/splitmix64.rs

rand_xoshiro/
splitmix64.rs
