tcp/util/
mod.rs

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1pub mod time;
2
3/// An array that derefs to a variable-length slice. Useful for storing variable-length data in a
4/// struct without allocating. The generic `N` must be a valid `u8`, so can only store up to
5/// `u8::MAX` items.
6#[derive(Copy, Clone, Debug)]
7pub struct SmallArrayBackedSlice<const N: usize, T> {
8    len: u8,
9    bytes: [T; N],
10}
11
12// we could avoid the `Default` and `Copy` requirements by using `MaybeUninit`, but it's not worth
13// the `unsafe` when we only plan to use this for integer arrays
14impl<const N: usize, T: Default + Copy> SmallArrayBackedSlice<N, T> {
15    // N isn't available from a constant context in `new()` for some reason so we need to do this
16    // check here, but it doesn't actually run unless we access `CHECK_N` from somewhere like
17    // `new()`
18    const CHECK_N: () = {
19        assert!(N <= u8::MAX as usize);
20    };
21
22    /// Returns `None` if there's not enough space.
23    pub fn new(bytes: &[T]) -> Option<Self> {
24        // force a compile-time check that `N` is a valid `u8`
25        #[allow(clippy::let_unit_value)]
26        let _ = Self::CHECK_N;
27
28        if bytes.len() > N {
29            return None;
30        }
31
32        let mut rv = Self::empty();
33
34        rv.len = bytes.len().try_into().unwrap();
35        rv.bytes[..bytes.len()].copy_from_slice(bytes);
36
37        Some(rv)
38    }
39
40    pub fn empty() -> Self {
41        // force a compile-time check that `N` is a valid `u8`
42        #[allow(clippy::let_unit_value)]
43        let _ = Self::CHECK_N;
44
45        Self {
46            len: 0,
47            bytes: [T::default(); N],
48        }
49    }
50}
51
52impl<const N: usize, T> std::ops::Deref for SmallArrayBackedSlice<N, T> {
53    type Target = [T];
54
55    fn deref(&self) -> &Self::Target {
56        &self.bytes[..(self.len as usize)]
57    }
58}
59
60impl<const N: usize, T> AsRef<[T]> for SmallArrayBackedSlice<N, T> {
61    fn as_ref(&self) -> &[T] {
62        self
63    }
64}
65
66/// Remove at most one item from a [`LinkedList`](std::collections::LinkedList).
67pub(crate) fn remove_from_list<T: Eq>(list: &mut std::collections::LinkedList<T>, item: &T) {
68    if let Some(pos) = list.iter().position(|e| e == item) {
69        let mut split_list = list.split_off(pos);
70        split_list.pop_front();
71        list.append(&mut split_list);
72    }
73}
74
75#[cfg(test)]
76mod tests {
77    use super::*;
78
79    #[test]
80    fn test_new_small_slice() {
81        SmallArrayBackedSlice::<3, u8>::empty();
82        SmallArrayBackedSlice::<3, u8>::new(&[]).unwrap();
83        SmallArrayBackedSlice::<3, u8>::new(&[1]).unwrap();
84        SmallArrayBackedSlice::<3, u8>::new(&[1, 2]).unwrap();
85        SmallArrayBackedSlice::<3, u8>::new(&[1, 2, 3]).unwrap();
86        assert!(SmallArrayBackedSlice::<3, u8>::new(&[1, 2, 3, 4]).is_none());
87    }
88
89    #[test]
90    fn test_deref_small_slice() {
91        let slice = SmallArrayBackedSlice::<3, u8>::empty();
92        assert!(slice.is_empty());
93
94        let slice = SmallArrayBackedSlice::<3, u8>::new(&[]).unwrap();
95        assert!(slice.is_empty());
96
97        let slice = SmallArrayBackedSlice::<3, u8>::new(&[1]).unwrap();
98        assert_eq!(slice.len(), 1);
99
100        let slice = SmallArrayBackedSlice::<3, u8>::new(&[1, 2, 3]).unwrap();
101        assert_eq!(slice.len(), 3);
102        assert_eq!(&*slice, &[1, 2, 3]);
103    }
104
105    #[test]
106    fn test_remove_from_list() {
107        let mut list: std::collections::LinkedList<u8> =
108            [1, 6, 2, 7, 3, 6, 4, 0].into_iter().collect();
109
110        fn to_vec<T: Clone>(list: &std::collections::LinkedList<T>) -> Vec<T> {
111            list.clone().into_iter().collect()
112        }
113
114        remove_from_list(&mut list, &3);
115        assert_eq!(&to_vec(&list), &[1, 6, 2, 7, 6, 4, 0]);
116
117        remove_from_list(&mut list, &6);
118        assert_eq!(&to_vec(&list), &[1, 2, 7, 6, 4, 0]);
119
120        remove_from_list(&mut list, &6);
121        assert_eq!(&to_vec(&list), &[1, 2, 7, 4, 0]);
122
123        remove_from_list(&mut list, &1);
124        assert_eq!(&to_vec(&list), &[2, 7, 4, 0]);
125
126        remove_from_list(&mut list, &0);
127        assert_eq!(&to_vec(&list), &[2, 7, 4]);
128
129        remove_from_list(&mut list, &7);
130        assert_eq!(&to_vec(&list), &[2, 4]);
131
132        remove_from_list(&mut list, &4);
133        assert_eq!(&to_vec(&list), &[2]);
134
135        remove_from_list(&mut list, &3);
136        assert_eq!(&to_vec(&list), &[2]);
137
138        remove_from_list(&mut list, &2);
139        assert_eq!(&to_vec(&list), &[]);
140
141        remove_from_list(&mut list, &2);
142        assert_eq!(&to_vec(&list), &[]);
143    }
144}
tcp/util/mod.rs

tcp/util/
mod.rs
