devela/num/rand/xorshift/
u32.rs

1// devela::num::rand::xorshift::u32
2//
3//! 32-bit version of XorShift.
4//
5
6use crate::{ConstDefault, Own, xorshift_basis};
7
8#[doc = crate::TAG_RAND!()]
9/// The `XorShift32` <abbr title="Pseudo-Random Number Generator">PRNG</abbr>.
10///
11/// It has a 32-bit state and generates 32-bit numbers.
12///
13/// This is the classic 32-bit *XorShift* algorithm by George Marsaglia.
14///
15/// The `BASIS` and triplet (`A`, `B`, `C`) values default to the canonical example.
16#[must_use]
17#[derive(Clone, Copy, Debug, PartialEq, Eq)]
18pub struct XorShift32<
19    const BASIS: usize = 1,
20    const A: usize = 5,
21    const B: usize = 17,
22    const C: usize = 13,
23>(u32);
24
25/// Creates a new PRNG initialized with the default fixed seed.
26impl Default for XorShift32 {
27    fn default() -> Self {
28        Self::DEFAULT
29    }
30}
31/// Creates a new PRNG initialized with the default fixed seed.
32impl ConstDefault for XorShift32 {
33    const DEFAULT: Self = Self::new_unchecked(Self::DEFAULT_SEED);
34}
35
36// private associated items
37impl<const BASIS: usize, const A: usize, const B: usize, const C: usize>
38    XorShift32<BASIS, A, B, C>
39{
40    const DEFAULT_SEED: u32 = 0xDEFA_0017;
41
42    #[cold] #[allow(dead_code)] #[rustfmt::skip]
43    const fn cold_path_default() -> Self { Self::new_unchecked(Self::DEFAULT_SEED) }
44}
45
46impl<const BASIS: usize, const A: usize, const B: usize, const C: usize>
47    XorShift32<BASIS, A, B, C>
48{
49    /// Returns a seeded `XorShift32` generator from the given 32-bit seed.
50    ///
51    /// If the seed is `0`, the default seed is used instead.
52    pub const fn new(seed: u32) -> Self {
53        if seed == 0 { Self::cold_path_default() } else { Self(seed) }
54    }
55
56    /// Returns a seeded `XorShift32` generator from the given 8-bit seed, unchecked.
57    ///
58    /// The seed must not be `0`, otherwise every result will also be `0`.
59    pub const fn new_unchecked(seed: u32) -> Self {
60        debug_assert![seed != 0, "Seed must be non-zero"];
61        Self(seed)
62    }
63
64    #[must_use]
65    /// Returns the PRNG's inner state as a raw snapshot.
66    pub const fn inner_state(self) -> u32 {
67        self.0
68    }
69    /// Restores the PRNG from the given state.
70    pub const fn from_state(state: u32) -> Self {
71        Self(state)
72    }
73
74    /// Returns the current random `u32`.
75    #[must_use]
76    pub const fn current_u32(&self) -> u32 {
77        self.0
78    }
79
80    /// Returns the next random `u32`.
81    //
82    // Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs"
83    #[must_use]
84    pub fn next_u32(&mut self) -> u32 {
85        let mut x = self.0;
86        xorshift_basis!(x, BASIS, (A, B, C));
87        self.0 = x;
88        x
89    }
90
91    /// Returns a copy of the next new random state.
92    pub const fn peek_next_state(&self) -> Self {
93        let mut x = self.0;
94        xorshift_basis!(x, BASIS, (A, B, C));
95        Self(x)
96    }
97
98    /// Returns both the next random state and the `u32` value.
99    pub const fn own_next_u32(self) -> Own<Self, u32> {
100        let s = self.peek_next_state();
101        let v = s.current_u32();
102        Own::new(s, v)
103    }
104}
105
106/// # Extra constructors
107impl<const BASIS: usize, const A: usize, const B: usize, const C: usize>
108    XorShift32<BASIS, A, B, C>
109{
110    /// Returns a seeded `XorShift32` generator from the given 32-bit seed.
111    ///
112    /// This is an alias of [`new`][Self#method.new].
113    pub const fn new1_u32(seed: u32) -> Self {
114        Self::new(seed)
115    }
116
117    /// Returns a seeded `XorShift32` generator from the given 2 × 16-bit seeds.
118    ///
119    /// The seeds will be joined in little endian order.
120    #[cfg(feature = "join")]
121    #[cfg_attr(nightly_doc, doc(cfg(feature = "join")))]
122    pub const fn new2_u16(seeds: [u16; 2]) -> Self {
123        Self::new(crate::Cast::<u32>::from_u16_le(seeds))
124    }
125
126    /// Returns a seeded `XorShift32` generator from the given 4 × 8-bit seeds.
127    ///
128    /// The seeds will be joined in little endian order.
129    pub const fn new4_u8(seeds: [u8; 4]) -> Self {
130        Self::new(u32::from_le_bytes(seeds))
131    }
132}
133
134#[cfg(all(feature = "dep_rand_core", feature = "join"))]
135#[cfg_attr(nightly_doc, doc(cfg(all(feature = "dep_rand_core", feature = "join"))))]
136mod impl_rand {
137    use crate::_dep::rand_core::{RngCore, SeedableRng};
138    use crate::{Cast, XorShift32};
139
140    impl<const BASIS: usize, const A: usize, const B: usize, const C: usize> RngCore
141        for XorShift32<BASIS, A, B, C>
142    {
143        /// Returns the next random `u32`.
144        fn next_u32(&mut self) -> u32 {
145            self.next_u32()
146        }
147
148        /// Returns the next 2 × random `u32` combined as a single `u64`.
149        fn next_u64(&mut self) -> u64 {
150            Cast::<u64>::from_u32_le([self.next_u32(), self.next_u32()])
151        }
152
153        fn fill_bytes(&mut self, dest: &mut [u8]) {
154            let mut i = 0;
155            while i < dest.len() {
156                let random_u32 = self.next_u32();
157                let bytes = random_u32.to_le_bytes();
158                let remaining = dest.len() - i;
159
160                if remaining >= 4 {
161                    dest[i..i + 4].copy_from_slice(&bytes);
162                    i += 4;
163                } else {
164                    dest[i..].copy_from_slice(&bytes[..remaining]);
165                    break;
166                }
167            }
168        }
169    }
170
171    impl<const BASIS: usize, const A: usize, const B: usize, const C: usize> SeedableRng
172        for XorShift32<BASIS, A, B, C>
173    {
174        type Seed = [u8; 4];
175
176        /// When seeded with zero this implementation uses the default seed
177        /// value as the cold path.
178        fn from_seed(seed: Self::Seed) -> Self {
179            if seed == [0; 4] {
180                Self::cold_path_default()
181            } else {
182                Self::new_unchecked(u32::from_le_bytes(seed))
183            }
184        }
185    }
186}
187
188/// 81 × good triplets for 32-bit xorshift. (243 Bytes)
189#[doc(hidden)]
190#[rustfmt::skip]
191#[allow(dead_code)]
192pub const XOROSHIFT_32_TRIPLETS: [(u8, u8, u8); 81] = [
193    ( 1, 3,10), ( 1, 5,16), ( 1, 5,19), ( 1, 9,29), ( 1,11, 6), ( 1,11,16),
194    ( 1,19, 3), ( 1,21,20), ( 1,27,27), ( 2, 5,15), ( 2, 5,21), ( 2, 7, 7),
195    ( 2, 7, 9), ( 2, 7,25), ( 2, 9,15), ( 2,15,17), ( 2,15,25), ( 2,21, 9),
196    ( 3, 1,14), ( 3, 3,26), ( 3, 3,28), ( 3, 3,29), ( 3, 5,20), ( 3, 5,22),
197    ( 3, 5,25), ( 3, 7,29), ( 3,13, 7), ( 3,23,25), ( 3,25,24), ( 3,27,11),
198    ( 4, 3,17), ( 4, 3,27), ( 4, 5,15), ( 5, 3,21), ( 5, 7,22), ( 5, 9, 7),
199    ( 5, 9,28), ( 5, 9,31), ( 5,13, 6), ( 5,15,17), ( 5,17,13), ( 5,21,12),
200    ( 5,27, 8), ( 5,27,21), ( 5,27,25), ( 5,27,28), ( 6, 1,11), ( 6, 3,17),
201    ( 6,17, 9), ( 6,21, 7), ( 6,21,13), ( 7, 1, 9), ( 7, 1,18), ( 7, 1,25),
202    ( 7,13,25), ( 7,17,21), ( 7,25,12), ( 7,25,20), ( 8, 7,23), ( 8, 9,23),
203    ( 9, 5, 1), ( 9, 5,25), ( 9,11,19), ( 9,21,16), (10, 9,21), (10, 9,25),
204    (11, 7,12), (11,7, 16), (11,17,13), (11,21,13), (12, 9,23), (13, 3,17),
205    (13, 3,27), (13,5, 19), (13,17,15), (14, 1,15), (14,13,15), (15, 1,29),
206    (17,15,20), (17,15,23), (17,15,26)
207];
devela/num/rand/xorshift/u32.rs

devela/num/rand/xorshift/
u32.rs
