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#![no_std]
#![feature(const_fn)]
use core::{
cell::UnsafeCell,
marker::PhantomData,
sync::atomic::{AtomicUsize, Ordering},
};
const CAPACITY: usize = 1024;
#[derive(Debug, PartialEq)]
pub enum Error {
BufferFull,
}
pub struct RingBuffer<T> {
head: AtomicUsize,
tail: AtomicUsize,
buf: UnsafeCell<[T; CAPACITY]>,
}
impl<T> RingBuffer<T>
where
T: Copy,
{
pub const fn new(default: T) -> Self {
Self {
head: AtomicUsize::new(0),
tail: AtomicUsize::new(0),
buf: UnsafeCell::new([default; CAPACITY]),
}
}
pub const fn split<'a>(&'a self) -> (Reader<T>, Writer<T>) {
let rbr = Reader {
rb: self as *const _,
_marker: PhantomData,
};
let rbw = Writer {
rb: self as *const _,
_marker: PhantomData,
};
(rbr, rbw)
}
}
pub struct Reader<'a, T> {
rb: *const RingBuffer<T>,
_marker: PhantomData<&'a ()>,
}
unsafe impl<T> Send for Reader<'_, T> where T: Send {}
unsafe impl<T> Sync for Reader<'_, T> {}
pub struct Writer<'a, T> {
rb: *const RingBuffer<T>,
_marker: PhantomData<&'a ()>,
}
unsafe impl<T> Send for Writer<'_, T> where T: Send {}
unsafe impl<T> Sync for Writer<'_, T> {}
impl<T> Reader<'_, T>
where
T: Copy,
{
pub fn len(&self) -> usize {
let rb: &mut RingBuffer<T> = unsafe { core::mem::transmute(self.rb) };
let h = rb.head.load(Ordering::SeqCst);
let t = rb.tail.load(Ordering::SeqCst);
let rc = (t + CAPACITY - h) % CAPACITY;
rc
}
pub fn is_empty(&self) -> bool {
self.len() == 0
}
pub fn shift(&mut self) -> Option<T> {
let rb: &mut RingBuffer<T> = unsafe { core::mem::transmute(self.rb) };
let h = rb.head.load(Ordering::SeqCst);
let t = rb.tail.load(Ordering::SeqCst);
if h == t {
None
} else {
let nh = (h + 1) % CAPACITY;
let rc = unsafe {
let buf = &mut *rb.buf.get();
Some(*buf.get_unchecked(h))
};
rb.head.store(nh, Ordering::SeqCst);
rc
}
}
}
impl<T> Iterator for Reader<'_, T>
where
T: Copy,
{
type Item = T;
fn next(&mut self) -> Option<Self::Item> {
self.shift()
}
}
impl<T> Writer<'_, T>
where
T: Copy,
{
pub fn unshift(&mut self, v: T) -> Result<(), Error> {
let rb: &mut RingBuffer<T> = unsafe { core::mem::transmute(self.rb) };
let h = rb.head.load(Ordering::SeqCst);
let t = rb.tail.load(Ordering::SeqCst);
let nt = (t + 1) % CAPACITY;
if nt == h {
Err(Error::BufferFull)
} else {
unsafe {
let buf = &mut *rb.buf.get();
*buf.get_unchecked_mut(t) = v;
}
rb.tail.store(nt, Ordering::SeqCst);
Ok(())
}
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn detects_empty() {
let rb = RingBuffer::<bool>::new(false);
let (mut rbr, mut rbw) = rb.split();
assert!(rbr.is_empty());
rbw.unshift(true).ok();
assert!(!rbr.is_empty());
rbr.shift();
assert!(rbr.is_empty());
}
#[test]
fn len_matches() {
let rb = RingBuffer::<bool>::new(false);
let (mut rbr, mut rbw) = rb.split();
for i in 0..CAPACITY - 1 {
assert_eq!(rbr.len(), i);
assert_eq!(rbw.unshift(true), Ok(()));
}
for i in 0..CAPACITY - 1 {
assert_eq!(rbr.len(), CAPACITY - 1 - i);
rbr.shift();
}
assert_eq!(rbr.len(), 0);
}
#[test]
fn can_wrap() {
let rb = RingBuffer::<usize>::new(0);
let (mut rbr, mut rbw) = rb.split();
for i in 0..CAPACITY - 1 {
assert_eq!(rbw.unshift(i), Ok(()))
}
for i in 0..CAPACITY - 1 {
assert_eq!(rbr.shift(), Some(i))
}
}
#[test]
fn cannot_overwrite() {
let rb = RingBuffer::<usize>::new(0);
let (mut rbr, mut rbw) = rb.split();
for i in 0..CAPACITY - 1 {
assert_eq!(rbw.unshift(i), Ok(()));
}
assert_eq!(rbw.unshift(0xffff), Err(Error::BufferFull));
rbr.shift();
assert_eq!(rbw.unshift(0xffff), Ok(()));
}
#[test]
fn can_iter() {
let rb = RingBuffer::<usize>::new(0);
let (rbr, mut rbw) = rb.split();
for i in 0..CAPACITY - 1 {
assert_eq!(rbw.unshift(i), Ok(()));
}
let mut i = 0;
for e in rbr {
assert_eq!(e, i);
i += 1;
}
}
}