98 lines
2.8 KiB
Rust
98 lines
2.8 KiB
Rust
use {crate::unreachable_unchecked, alloc::vec::Vec, core::mem::replace};
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#[derive(Debug)]
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enum Entry<T> {
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Vacant(usize),
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Occupied(T),
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}
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#[derive(Debug)]
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pub(crate) struct Slab<T> {
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next_vacant: usize,
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entries: Vec<Entry<T>>,
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}
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impl<T> Slab<T> {
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pub fn new() -> Self {
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Slab {
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next_vacant: !0,
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entries: Vec::new(),
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}
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}
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/// Inserts value into this linked vec and returns index
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/// at which value can be accessed in constant time.
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pub fn insert(&mut self, value: T) -> usize {
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if self.next_vacant >= self.entries.len() {
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self.entries.push(Entry::Occupied(value));
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self.entries.len() - 1
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} else {
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match *unsafe { self.entries.get_unchecked(self.next_vacant) } {
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Entry::Vacant(next_vacant) => {
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unsafe {
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*self.entries.get_unchecked_mut(self.next_vacant) = Entry::Occupied(value);
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}
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replace(&mut self.next_vacant, next_vacant)
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}
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_ => unsafe { unreachable_unchecked() },
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}
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}
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}
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pub fn len(&self) -> usize {
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self.entries.len()
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}
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pub unsafe fn get_unchecked(&self, index: usize) -> &T {
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debug_assert!(index < self.len());
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match self.entries.get_unchecked(index) {
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Entry::Occupied(value) => value,
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_ => unreachable_unchecked(),
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}
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}
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pub unsafe fn get_unchecked_mut(&mut self, index: usize) -> &mut T {
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debug_assert!(index < self.len());
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match self.entries.get_unchecked_mut(index) {
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Entry::Occupied(value) => value,
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_ => unreachable_unchecked(),
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}
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}
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pub fn get(&self, index: usize) -> &T {
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match self.entries.get(index) {
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Some(Entry::Occupied(value)) => value,
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_ => panic!("Invalid index"),
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}
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}
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pub fn get_mut(&mut self, index: usize) -> &mut T {
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match self.entries.get_mut(index) {
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Some(Entry::Occupied(value)) => value,
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_ => panic!("Invalid index"),
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}
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}
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pub unsafe fn remove_unchecked(&mut self, index: usize) -> T {
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let entry = replace(
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self.entries.get_unchecked_mut(index),
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Entry::Vacant(self.next_vacant),
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);
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self.next_vacant = index;
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match entry {
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Entry::Occupied(value) => value,
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_ => unreachable_unchecked(),
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}
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}
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pub fn remove(&mut self, index: usize) -> T {
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match self.entries.get_mut(index) {
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Some(Entry::Occupied(_)) => unsafe { self.remove_unchecked(index) },
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_ => panic!("Invalid index"),
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}
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}
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}
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