calc_lib/
cache.rs

1/// Unit tests.
2#[cfg(test)]
3mod tests;
4use core::ops::Index;
5/// A cache of `N` `T`s. When the cache is filled up,
6/// a new entry overwrites the oldest entry. `Cache<T, N>`
7/// cannot be expanded or shrunk.
8#[derive(Debug)]
9pub struct Cache<T, const N: usize> {
10    /// The cache of `T`s.
11    vals: [T; N],
12    /// The number of `T`s in our cache. Once
13    /// `N` number of `T`s have been cached, this will
14    /// always be `N`.
15    len: usize,
16    /// The index position of the next insert.
17    next_head: usize,
18}
19impl<T, const N: usize> Cache<T, N> {
20    /// Returns the number of items cached.
21    /// This will always return `N` once at least
22    /// `N` items have been cached.
23    #[inline]
24    pub const fn len(&self) -> usize {
25        self.len
26    }
27    /// Returns true iff no items have been cached.
28    #[inline]
29    pub const fn is_empty(&self) -> bool {
30        self.len == 0
31    }
32}
33/// Implements the functions `get`, `get_unsafe`, and `push` as well as `Index<usize, Output = T>`
34/// for each of the passed usize literals.
35/// Only powers of two are allowed to be passed due to how the above functions are implemented.
36/// If any other value is passed, the implementation of those functions will be wrong.
37macro_rules! cache {
38    ( $( $x:literal),* ) => {
39        $(
40impl<T> Cache<T, $x> {
41    /// Returns `Some(&T)` iff there is an item located
42    /// at index `idx`. Indexing begins at the newest
43    /// entry (i.e., `self.get(0)` will return the most recent entry
44    /// iff at least one item has been cached).
45    #[inline]
46    pub fn get(&self, idx: usize) -> Option<&T> {
47        (idx < self.len).then(|| self.vals.index(self.next_head.wrapping_sub(1).wrapping_sub(idx) & ($x - 1)))
48    }
49    /// Returns a `&T` at index position `idx % N`. In the event
50    /// `(idx % N) >= self.len()`, then `&T` references the
51    /// default value of `T` that was inserted at creation but *not*
52    /// actually inserted via `push`.
53    ///
54    /// # Correctness
55    ///
56    /// `idx < self.len()`; otherwise a value that was not actually inserted will be returned.
57    #[inline]
58    pub fn get_unchecked(&self, idx: usize) -> &T {
59        self.vals.index(self.next_head.wrapping_sub(1).wrapping_sub(idx) & ($x - 1))
60    }
61    /// Adds `val` to the cache. In the event `N` values have already been cached,
62    /// the oldest entry is overwritten.
63    #[expect(clippy::arithmetic_side_effects, reason = "must, and overflow is not possible")]
64    #[expect(clippy::indexing_slicing, reason = "wont panic since next_head is always correct")]
65    #[inline]
66    pub fn push(&mut self, val: T) {
67        if self.len < $x {
68            self.len += 1;
69        }
70        // next_head is always less than or equal to N since we only implement
71        // this function when N is a power of 2.
72        self.vals[self.next_head] = val;
73        self.next_head = (self.next_head + 1) & ($x - 1);
74    }
75}
76impl<T> Index<usize> for Cache<T, $x> {
77    type Output = T;
78    #[inline]
79    fn index(&self, index: usize) -> &Self::Output {
80        self.get(index).unwrap()
81    }
82}
83        )*
84    };
85}
86// MUST only pass powers of two! Anything else will lead to wrong code.
87cache!(
88    0x1,
89    0x2,
90    0x4,
91    0x8,
92    0x10,
93    0x20,
94    0x40,
95    0x80,
96    0x100,
97    0x200,
98    0x400,
99    0x800,
100    0x1000,
101    0x2000,
102    0x4000,
103    0x8000,
104    0x0001_0000,
105    0x0002_0000,
106    0x0004_0000,
107    0x0008_0000,
108    0x0010_0000,
109    0x0020_0000,
110    0x0040_0000,
111    0x0080_0000,
112    0x0100_0000,
113    0x0200_0000,
114    0x0400_0000,
115    0x0800_0000,
116    0x1000_0000,
117    0x2000_0000,
118    0x4000_0000,
119    0x8000_0000,
120    0x0001_0000_0000,
121    0x0002_0000_0000,
122    0x0004_0000_0000,
123    0x0008_0000_0000,
124    0x0010_0000_0000,
125    0x0020_0000_0000,
126    0x0040_0000_0000,
127    0x0080_0000_0000,
128    0x0100_0000_0000,
129    0x0200_0000_0000,
130    0x0400_0000_0000,
131    0x0800_0000_0000,
132    0x1000_0000_0000,
133    0x2000_0000_0000,
134    0x4000_0000_0000,
135    0x8000_0000_0000,
136    0x0001_0000_0000_0000,
137    0x0002_0000_0000_0000,
138    0x0004_0000_0000_0000,
139    0x0008_0000_0000_0000,
140    0x0010_0000_0000_0000,
141    0x0020_0000_0000_0000,
142    0x0040_0000_0000_0000,
143    0x0080_0000_0000_0000,
144    0x0100_0000_0000_0000,
145    0x0200_0000_0000_0000,
146    0x0400_0000_0000_0000,
147    0x0800_0000_0000_0000,
148    0x1000_0000_0000_0000,
149    0x2000_0000_0000_0000,
150    0x4000_0000_0000_0000,
151    0x8000_0000_0000_0000
152);
153impl<T, const N: usize> Cache<T, N>
154where
155    [T; N]: Default,
156{
157    /// Returns an instance of itself pre-loaded with
158    /// the `N` instances of the default value of `T`.
159    /// Note these default instances are treated as though
160    /// they don't exist (i.e., `self.is_empty()` will return true).
161    #[inline]
162    #[must_use]
163    pub fn new() -> Self {
164        Self::default()
165    }
166}
167impl<T, const N: usize> Default for Cache<T, N>
168where
169    [T; N]: Default,
170{
171    #[inline]
172    fn default() -> Self {
173        Self {
174            vals: Default::default(),
175            len: 0,
176            next_head: 0,
177        }
178    }
179}
calc_lib/cache.rs

calc_lib/
cache.rs
