rand/rngs/
xoshiro128plusplus.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::{SeedableRng, TryRng, utils};
11#[cfg(feature = "serde")]
12use serde::{Deserialize, Serialize};
13
14/// A xoshiro128++ random number generator.
15///
16/// The xoshiro128++ 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 `xoshiro128plusplus.c`
20/// reference source code](http://xoshiro.di.unimi.it/xoshiro128plusplus.c) by
21/// David Blackman and Sebastiano Vigna.
22#[derive(#[automatically_derived]
impl ::core::fmt::Debug for Xoshiro128PlusPlus {
    #[inline]
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        ::core::fmt::Formatter::debug_struct_field1_finish(f,
            "Xoshiro128PlusPlus", "s", &&self.s)
    }
}Debug, #[automatically_derived]
impl ::core::clone::Clone for Xoshiro128PlusPlus {
    #[inline]
    fn clone(&self) -> Xoshiro128PlusPlus {
        Xoshiro128PlusPlus { s: ::core::clone::Clone::clone(&self.s) }
    }
}Clone, #[automatically_derived]
impl ::core::cmp::PartialEq for Xoshiro128PlusPlus {
    #[inline]
    fn eq(&self, other: &Xoshiro128PlusPlus) -> bool { self.s == other.s }
}PartialEq, #[automatically_derived]
impl ::core::cmp::Eq for Xoshiro128PlusPlus {
    #[inline]
    #[doc(hidden)]
    #[coverage(off)]
    fn assert_receiver_is_total_eq(&self) {
        let _: ::core::cmp::AssertParamIsEq<[u32; 4]>;
    }
}Eq)]
23#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
24pub struct Xoshiro128PlusPlus {
25    s: [u32; 4],
26}
27
28impl SeedableRng for Xoshiro128PlusPlus {
29    type Seed = [u8; 16];
30
31    /// Create a new `Xoshiro128PlusPlus`.  If `seed` is entirely 0, it will be
32    /// mapped to a different seed.
33    #[inline]
34    fn from_seed(seed: [u8; 16]) -> Xoshiro128PlusPlus {
35        let state = utils::read_words(&seed);
36        // Check for zero on aligned integers for better code generation.
37        // Furtermore, seed_from_u64(0) will expand to a constant when optimized.
38        if state.iter().all(|&x| x == 0) {
39            return Self::seed_from_u64(0);
40        }
41        Xoshiro128PlusPlus { s: state }
42    }
43
44    /// Create a new `Xoshiro128PlusPlus` from a `u64` seed.
45    ///
46    /// This uses the SplitMix64 generator internally.
47    #[inline]
48    fn seed_from_u64(mut state: u64) -> Self {
49        const PHI: u64 = 0x9e3779b97f4a7c15;
50        let mut s = [0; 4];
51        for i in s.chunks_exact_mut(2) {
52            state = state.wrapping_add(PHI);
53            let mut z = state;
54            z = (z ^ (z >> 30)).wrapping_mul(0xbf58476d1ce4e5b9);
55            z = (z ^ (z >> 27)).wrapping_mul(0x94d049bb133111eb);
56            z = z ^ (z >> 31);
57            i[0] = z as u32;
58            i[1] = (z >> 32) as u32;
59        }
60        // By using a non-zero PHI we are guaranteed to generate a non-zero state
61        // Thus preventing a recursion between from_seed and seed_from_u64.
62        if true {
    match (&s, &[0; 4]) {
        (left_val, right_val) => {
            if *left_val == *right_val {
                let kind = ::core::panicking::AssertKind::Ne;
                ::core::panicking::assert_failed(kind, &*left_val,
                    &*right_val, ::core::option::Option::None);
            }
        }
    };
};debug_assert_ne!(s, [0; 4]);
63        Xoshiro128PlusPlus { s }
64    }
65}
66
67impl TryRng for Xoshiro128PlusPlus {
68    type Error = Infallible;
69
70    #[inline]
71    fn try_next_u32(&mut self) -> Result<u32, Infallible> {
72        let res = self.s[0]
73            .wrapping_add(self.s[3])
74            .rotate_left(7)
75            .wrapping_add(self.s[0]);
76
77        let t = self.s[1] << 9;
78
79        self.s[2] ^= self.s[0];
80        self.s[3] ^= self.s[1];
81        self.s[1] ^= self.s[2];
82        self.s[0] ^= self.s[3];
83
84        self.s[2] ^= t;
85
86        self.s[3] = self.s[3].rotate_left(11);
87
88        Ok(res)
89    }
90
91    #[inline]
92    fn try_next_u64(&mut self) -> Result<u64, Infallible> {
93        utils::next_u64_via_u32(self)
94    }
95
96    #[inline]
97    fn try_fill_bytes(&mut self, dst: &mut [u8]) -> Result<(), Infallible> {
98        utils::fill_bytes_via_next_word(dst, || self.try_next_u32())
99    }
100}
101
102#[cfg(test)]
103mod tests {
104    use super::Xoshiro128PlusPlus;
105    use rand_core::{Rng, SeedableRng};
106
107    #[test]
108    fn reference() {
109        let mut rng =
110            Xoshiro128PlusPlus::from_seed([1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0]);
111        // These values were produced with the reference implementation:
112        // http://xoshiro.di.unimi.it/xoshiro128plusplus.c
113        let expected = [
114            641, 1573767, 3222811527, 3517856514, 836907274, 4247214768, 3867114732, 1355841295,
115            495546011, 621204420,
116        ];
117        for &e in &expected {
118            assert_eq!(rng.next_u32(), e);
119        }
120    }
121
122    #[test]
123    fn stable_seed_from_u64_and_from_seed() {
124        // We don't guarantee value-stability for SmallRng but this
125        // could influence keeping stability whenever possible (e.g. after optimizations).
126        let mut rng = Xoshiro128PlusPlus::seed_from_u64(0);
127        // from_seed([0; 16]) should produce the same state as seed_from_u64(0).
128        let mut rng_from_seed_0 = Xoshiro128PlusPlus::from_seed([0; 16]);
129        let expected = [
130            1179900579, 1938959192, 3089844957, 3657088315, 1015453891, 479942911, 3433842246,
131            669252886, 3985671746, 2737205563,
132        ];
133        for &e in &expected {
134            assert_eq!(rng.next_u32(), e);
135            assert_eq!(rng_from_seed_0.next_u32(), e);
136        }
137    }
138}
rand/rngs/xoshiro128plusplus.rs

rand/rngs/
xoshiro128plusplus.rs
