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use core::fmt;
use core::mem::MaybeUninit;
use core::ops::{Index, IndexMut};
use core::{ptr, slice};
pub struct VecDeque<T, const N: usize> {
buf: MaybeUninit<[T; N]>,
end: usize,
start: usize,
is_full: bool,
}
impl<T, const N: usize> VecDeque<T, N> {
const CAPACITY: usize = N;
pub const fn new() -> Self {
VecDeque {
buf: MaybeUninit::uninit(),
end: 0,
start: 0,
is_full: false,
}
}
fn ptr(&self) -> *mut T {
self.buf.as_ptr() as *mut T
}
pub fn capacity(&self) -> usize {
Self::CAPACITY
}
pub fn len(&self) -> usize {
let start = self.start;
let end = self.end;
if self.is_full() {
self.capacity()
} else if end >= start {
end - start
} else {
self.capacity() - start + end
}
}
pub fn is_empty(&self) -> bool {
self.start == self.end && !self.is_full
}
pub fn is_full(&self) -> bool {
self.is_full
}
#[inline]
unsafe fn buffer_read(&mut self, off: usize) -> T {
ptr::read(self.ptr().add(off))
}
#[inline]
unsafe fn buffer_write(&mut self, off: usize, value: T) {
ptr::write(self.ptr().add(off), value);
}
#[inline]
fn wrap_add(&self, idx: usize, addend: usize) -> usize {
let (index, overflow) = idx.overflowing_add(addend);
if index >= self.capacity() || overflow {
index.wrapping_sub(self.capacity())
} else {
index
}
}
#[inline]
fn wrap_sub(&self, idx: usize, subtrahend: usize) -> usize {
let (index, overflow) = idx.overflowing_sub(subtrahend);
if overflow {
index.wrapping_add(self.capacity())
} else {
index
}
}
pub fn get(&self, index: usize) -> Option<&T> {
if index < self.len() {
let idx = self.wrap_add(self.start, index);
unsafe { Some(&*self.ptr().add(idx)) }
} else {
None
}
}
pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
if index < self.len() {
let idx = self.wrap_add(self.start, index);
unsafe { Some(&mut *self.ptr().add(idx)) }
} else {
None
}
}
pub fn as_slices(&self) -> (&[T], &[T]) {
let ptr = self.ptr() as *const T;
if self.end >= self.start && !self.is_full {
(
unsafe { slice::from_raw_parts(ptr.add(self.start), self.end - self.start) },
&mut [],
)
} else {
(
unsafe { slice::from_raw_parts(ptr.add(self.start), N - self.start) },
unsafe { slice::from_raw_parts(ptr, self.end) },
)
}
}
pub fn as_mut_slices(&mut self) -> (&mut [T], &mut [T]) {
let ptr = self.ptr();
if self.end >= self.start && !self.is_full {
(
unsafe { slice::from_raw_parts_mut(ptr.add(self.start), self.end - self.start) },
&mut [],
)
} else {
(
unsafe { slice::from_raw_parts_mut(ptr.add(self.start), N - self.start) },
unsafe { slice::from_raw_parts_mut(ptr, self.end) },
)
}
}
pub fn clear(&mut self) {
let (a, b) = self.as_mut_slices();
unsafe { ptr::drop_in_place(a) };
unsafe { ptr::drop_in_place(b) };
self.end = 0;
self.start = 0;
self.is_full = false;
}
pub fn pop_front(&mut self) -> Option<T> {
if self.is_empty() {
None
} else {
let start = self.start;
self.start = self.wrap_add(self.start, 1);
if self.is_full {
self.is_full = false;
}
unsafe { Some(self.buffer_read(start)) }
}
}
pub fn pop_back(&mut self) -> Option<T> {
if self.is_empty() {
None
} else {
self.end = self.wrap_sub(self.end, 1);
let end = self.end;
if self.is_full {
self.is_full = false;
}
unsafe { Some(self.buffer_read(end)) }
}
}
pub fn push_front(&mut self, value: T) -> Result<(), T> {
if self.is_full() {
return Err(value);
}
if self.len() == self.capacity() - 1 {
self.is_full = true;
}
self.start = self.wrap_sub(self.start, 1);
unsafe { self.buffer_write(self.start, value) };
Ok(())
}
pub fn push_back(&mut self, value: T) -> Result<(), T> {
if self.is_full() {
return Err(value);
}
if self.len() == self.capacity() - 1 {
self.is_full = true;
}
unsafe { self.buffer_write(self.end, value) };
self.end = self.wrap_add(self.end, 1);
Ok(())
}
}
impl<T, const N: usize> Index<usize> for VecDeque<T, N> {
type Output = T;
#[inline]
fn index(&self, index: usize) -> &T {
self.get(index).expect("Out of bounds access")
}
}
impl<T, const N: usize> IndexMut<usize> for VecDeque<T, N> {
#[inline]
fn index_mut(&mut self, index: usize) -> &mut T {
self.get_mut(index).expect("Out of bounds access")
}
}
impl<T: fmt::Debug, const N: usize> fmt::Debug for VecDeque<T, N> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Debug::fmt(&self.as_slices(), f)
}
}
impl<T, const N: usize> Drop for VecDeque<T, N> {
fn drop(&mut self) {
self.clear()
}
}
