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use slab::Slab;
/// Buffers frames for multiple streams.
#[derive(Debug)]
pub struct Buffer<T> {
slab: Slab<Slot<T>>,
}
/// A sequence of frames in a `Buffer`
#[derive(Debug)]
pub struct Deque {
indices: Option<Indices>,
}
/// Tracks the head & tail for a sequence of frames in a `Buffer`.
#[derive(Debug, Default, Copy, Clone)]
struct Indices {
head: usize,
tail: usize,
}
#[derive(Debug)]
struct Slot<T> {
value: T,
next: Option<usize>,
}
impl<T> Buffer<T> {
pub fn new() -> Self {
Buffer { slab: Slab::new() }
}
}
impl Deque {
pub fn new() -> Self {
Deque { indices: None }
}
pub fn is_empty(&self) -> bool {
self.indices.is_none()
}
pub fn push_back<T>(&mut self, buf: &mut Buffer<T>, value: T) {
let key = buf.slab.insert(Slot { value, next: None });
match self.indices {
Some(ref mut idxs) => {
buf.slab[idxs.tail].next = Some(key);
idxs.tail = key;
}
None => {
self.indices = Some(Indices {
head: key,
tail: key,
});
}
}
}
pub fn push_front<T>(&mut self, buf: &mut Buffer<T>, value: T) {
let key = buf.slab.insert(Slot { value, next: None });
match self.indices {
Some(ref mut idxs) => {
buf.slab[key].next = Some(idxs.head);
idxs.head = key;
}
None => {
self.indices = Some(Indices {
head: key,
tail: key,
});
}
}
}
pub fn pop_front<T>(&mut self, buf: &mut Buffer<T>) -> Option<T> {
match self.indices {
Some(mut idxs) => {
let mut slot = buf.slab.remove(idxs.head);
if idxs.head == idxs.tail {
assert!(slot.next.is_none());
self.indices = None;
} else {
idxs.head = slot.next.take().unwrap();
self.indices = Some(idxs);
}
Some(slot.value)
}
None => None,
}
}
}