urng 0.4.5

Universal Random Number Generator
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149

use crate::rng32::SplitMix32;
use crate::{rng::Rng32, wrap};
use std::num::Wrapping;

// --- Xorshift32 ---

/// A 32-bit Xorshift random number generator.
///
/// This generator uses a shift-register based algorithm.
///
/// # Examples
///
/// ```
/// use urng::prelude::*;
///
/// let mut rng = Xorshift32::new(1);
/// let _ = rng.nextu();
/// ```
#[repr(C)]
pub struct Xorshift32 {
    a: Wrapping<u32>,
}

impl Xorshift32 {
    /// Creates a new `Xorshift32` instance seeded with the given value.
    pub fn new(seed: u32) -> Self {
        let mut sm = SplitMix32::new(seed);
        Self {
            a: wrap!(sm.nextu()),
        }
    }
}

impl Rng32 for Xorshift32 {
    #[inline]
    fn nextu(&mut self) -> u32 {
        let x = self.a;
        self.a = x ^ (x << 13);
        self.a ^= self.a >> 17;
        self.a ^= self.a << 5;
        self.a.0
    }
}

// --- Xorshift128 ---

/// A 128-bit Xorshift random number generator.
///
/// Produces 32-bit output from a 128-bit internal state.
/// Period: 2^128 - 1.
///
/// # Examples
///
/// ```
/// use urng::prelude::*;
///
/// let mut rng = Xorshift128::new(1);
/// let _ = rng.nextu();
/// assert!(rng.randi(1, 100) >= 1);
/// ```
#[repr(C)]
pub struct Xorshift128 {
    x: [u32; 4],
}

impl Xorshift128 {
    /// Creates a new `Xorshift128` instance.
    ///
    /// Each seed element is OR-ed with 1 to prevent an all-zero state.
    pub fn new(seed: u32) -> Self {
        let mut sm = SplitMix32::new(seed);
        Self {
            x: [sm.nextu(), sm.nextu(), sm.nextu(), sm.nextu()],
        }
    }
}

impl Rng32 for Xorshift128 {
    #[inline]
    fn nextu(&mut self) -> u32 {
        let mut t = self.x[3];
        t ^= t << 11;
        t ^= t >> 8;
        let s = self.x[0];
        (self.x[1], self.x[2], self.x[3]) = (s, self.x[1], self.x[2]);
        self.x[0] = t ^ s ^ (s >> 19);
        self.x[0]
    }
}

/// A XORWOW random number generator.
///
/// This generator combines a Xorshift-based algorithm with a Weyl sequence (linear counter).
/// It has a state of 192 bits (5 x 32-bit state + 32-bit counter).
/// This is the default generator used in NVIDIA cuRAND.
///
/// # Examples
///
/// ```
/// use urng::prelude::*;
///
/// let mut rng = Xorwow::new(1);
/// assert_eq!(rng.nextu(), 3932718581);
/// ```
#[repr(C)]
pub struct Xorwow {
    x: [Wrapping<u32>; 5],
    c: Wrapping<u32>,
}

impl Xorwow {
    /// Creates a new `Xorwow` instance seeded with the given value.
    ///
    pub fn new(seed: u32) -> Self {
        let mut sm = SplitMix32::new(seed);
        Self {
            x: wrap![sm.nextu(), sm.nextu(), sm.nextu(), sm.nextu(), sm.nextu()],
            c: wrap!(sm.nextu()),
        }
    }
}

impl Rng32 for Xorwow {
    #[inline]
    fn nextu(&mut self) -> u32 {
        let mut t = self.x[4];

        let s = self.x[0];
        self.x[4] = self.x[3];
        self.x[3] = self.x[2];
        self.x[2] = self.x[1];
        self.x[1] = s;

        t ^= t >> 2;
        t ^= t << 1;
        t ^= s ^ (s << 4);
        self.x[0] = t;
        self.c += wrap!(362437);
        (t + self.c).0
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    crate::safe_test!(Xorshift32);
    crate::safe_test!(Xorwow);
}