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1421319dcf
Rename it to SmallVec, make it more generic and switch NAK to it. Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com> Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31409>
83 lines
2.7 KiB
Rust
83 lines
2.7 KiB
Rust
// Copyright © 2022 Collabora, Ltd.
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// SPDX-License-Identifier: MIT
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/// `SmallVec` is an optimized data structure that handles collections of items.
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/// It is designed to avoid allocating a `Vec` unless multiple items are present.
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///
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/// # Variants
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///
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/// * `None` - Represents an empty collection, no items are stored.
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/// * `One(T)` - Stores a single item without allocating a `Vec`.
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/// * `Many(Vec<T>)` - Stores multiple items in a heap-allocated `Vec`.
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///
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/// This helps to reduce the amount of Vec's allocated in the optimization passes.
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pub enum SmallVec<T> {
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None,
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One(T),
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Many(Vec<T>),
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}
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impl<T> SmallVec<T> {
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/// Adds an item to the `SmallVec`.
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///
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/// If the collection is empty (`None`), the item is stored as `One`.
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/// If the collection has one item (`One`), it transitions to `Many` and both items are stored in a `Vec`.
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/// If the collection is already in the `Many` variant, the new item is pushed into the existing `Vec`.
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///
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/// # Arguments
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///
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/// * `item` - The item to be added.
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///
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/// # Example
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///
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/// ```
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/// let mut vec: SmallVec<String> = SmallVec::None;
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/// vec.push("Hello".to_string());
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/// vec.push("World".to_string());
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/// ```
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pub fn push(&mut self, i: T) {
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match self {
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SmallVec::None => {
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*self = SmallVec::One(i);
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}
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SmallVec::One(_) => {
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*self = match std::mem::replace(self, SmallVec::None) {
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SmallVec::One(o) => SmallVec::Many(vec![o, i]),
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_ => panic!("Not a One"),
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};
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}
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SmallVec::Many(v) => {
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v.push(i);
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}
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}
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}
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/// Returns a mutable reference to the last item in the `SmallVec`, if it exists.
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///
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/// * If the collection is empty (`None`), it returns `None`.
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/// * If the collection has one item (`One`), it returns a mutable reference to that item.
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/// * If the collection has multiple items (`Many`), it returns a mutable reference to the last item in the `Vec`.
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///
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/// # Returns
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///
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/// * `Option<&mut T>` - A mutable reference to the last item, or `None` if the collection is empty.
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///
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/// # Example
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///
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/// ```
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/// let mut vec: SmallVec<i32> = SmallVec::None;
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/// vec.push(1);
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/// vec.push(2);
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///
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/// if let Some(last) = vec.last_mut() {
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/// *last = 10; // Modify the last element.
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/// }
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/// ```
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pub fn last_mut(&mut self) -> Option<&mut T> {
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match self {
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SmallVec::None => None,
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SmallVec::One(item) => Some(item),
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SmallVec::Many(v) => v.last_mut(),
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}
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}
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}
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