aligned 0.4.2

//! A newtype with alignment of at least `A` bytes
//!
//! # Examples
//!
//! ```
//! use std::mem;
//!
//! use aligned::{Aligned, A2, A4, A16};
//!
//! // Array aligned to a 2 byte boundary
//! static X: Aligned<A2, [u8; 3]> = Aligned([0; 3]);
//!
//! // Array aligned to a 4 byte boundary
//! static Y: Aligned<A4, [u8; 3]> = Aligned([0; 3]);
//!
//! // Unaligned array
//! static Z: [u8; 3] = [0; 3];
//!
//! // You can allocate the aligned arrays on the stack too
//! let w: Aligned<A16, _> = Aligned([0u8; 3]);
//!
//! assert_eq!(mem::align_of_val(&X), 2);
//! assert_eq!(mem::align_of_val(&Y), 4);
//! assert_eq!(mem::align_of_val(&Z), 1);
//! assert_eq!(mem::align_of_val(&w), 16);
//! ```

#![deny(missing_docs)]
#![deny(warnings)]
#![cfg_attr(not(test), no_std)]

use core::{
    borrow::{Borrow, BorrowMut},
    cmp::Ordering,
    fmt::{Debug, Display},
    hash::{Hash, Hasher},
    ops,
};

use as_slice::{AsMutSlice, AsSlice};

/// A marker trait for an alignment value.
pub trait Alignment: Copy + sealed::Sealed {}

impl Alignment for A1 {}
impl Alignment for A2 {}
impl Alignment for A4 {}
impl Alignment for A8 {}
impl Alignment for A16 {}
impl Alignment for A32 {}
impl Alignment for A64 {}

mod sealed {
    pub trait Sealed {}

    impl Sealed for super::A1 {}
    impl Sealed for super::A2 {}
    impl Sealed for super::A4 {}
    impl Sealed for super::A8 {}
    impl Sealed for super::A16 {}
    impl Sealed for super::A32 {}
    impl Sealed for super::A64 {}
}

/// 1-byte alignment
#[derive(Clone, Copy)]
#[repr(align(1))]
pub struct A1;

/// 2-byte alignment
#[derive(Clone, Copy)]
#[repr(align(2))]
pub struct A2;

/// 4-byte alignment
#[derive(Clone, Copy)]
#[repr(align(4))]
pub struct A4;

/// 8-byte alignment
#[derive(Clone, Copy)]
#[repr(align(8))]
pub struct A8;

/// 16-byte alignment
#[derive(Clone, Copy)]
#[repr(align(16))]
pub struct A16;

/// 32-byte alignment
#[derive(Clone, Copy)]
#[repr(align(32))]
pub struct A32;

/// 64-byte alignment
#[derive(Clone, Copy)]
#[repr(align(64))]
pub struct A64;

/// A newtype with alignment of at least `A` bytes
#[repr(C)]
pub struct Aligned<A, T>
where
    T: ?Sized,
{
    _alignment: [A; 0],
    value: T,
}

/// Changes the alignment of `value` to be at least `A` bytes
#[allow(non_snake_case)]
pub const fn Aligned<A, T>(value: T) -> Aligned<A, T> {
    Aligned {
        _alignment: [],
        value,
    }
}

impl<A, T> ops::Deref for Aligned<A, T>
where
    A: Alignment,
    T: ?Sized,
{
    type Target = T;

    fn deref(&self) -> &T {
        &self.value
    }
}

impl<A, T> ops::DerefMut for Aligned<A, T>
where
    A: Alignment,
    T: ?Sized,
{
    fn deref_mut(&mut self) -> &mut T {
        &mut self.value
    }
}

impl<A, T> ops::Index<ops::RangeTo<usize>> for Aligned<A, [T]>
where
    A: Alignment,
{
    type Output = Aligned<A, [T]>;

    fn index(&self, range: ops::RangeTo<usize>) -> &Aligned<A, [T]> {
        unsafe { &*(&self.value[range] as *const [T] as *const Aligned<A, [T]>) }
    }
}

impl<A, T> AsSlice for Aligned<A, T>
where
    A: Alignment,
    T: AsSlice,
{
    type Element = T::Element;

    fn as_slice(&self) -> &[T::Element] {
        T::as_slice(&**self)
    }
}

impl<A, T> AsMutSlice for Aligned<A, T>
where
    A: Alignment,
    T: AsMutSlice,
{
    fn as_mut_slice(&mut self) -> &mut [T::Element] {
        T::as_mut_slice(&mut **self)
    }
}

impl<A, T> Borrow<T> for Aligned<A, T>
where
    A: Alignment,
{
    fn borrow(&self) -> &T {
        &self.value
    }
}

impl<A, T> BorrowMut<T> for Aligned<A, T>
where
    A: Alignment,
{
    fn borrow_mut(&mut self) -> &mut T {
        &mut self.value
    }
}

impl<A, T> Borrow<[<Aligned<A, T> as AsSlice>::Element]> for Aligned<A, T>
where
    A: Alignment,
    Aligned<A, T>: AsSlice,
{
    fn borrow(&self) -> &[<Aligned<A, T> as AsSlice>::Element] {
        self.as_slice()
    }
}

impl<A, T> BorrowMut<[<Aligned<A, T> as AsSlice>::Element]> for Aligned<A, T>
where
    A: Alignment,
    Aligned<A, T>: AsMutSlice,
{
    fn borrow_mut(&mut self) -> &mut [<Aligned<A, T> as AsSlice>::Element] {
        self.as_mut_slice()
    }
}

impl<A, T> Clone for Aligned<A, T>
where
    A: Alignment,
    T: Clone,
{
    fn clone(&self) -> Self {
        Self {
            _alignment: [],
            value: self.value.clone(),
        }
    }
}

impl<A, T> Copy for Aligned<A, T>
where
    A: Alignment,
    T: Copy,
{
}

impl<A, T> Default for Aligned<A, T>
where
    A: Alignment,
    T: Default,
{
    fn default() -> Self {
        Self {
            _alignment: [],
            value: Default::default(),
        }
    }
}

impl<A, T> Debug for Aligned<A, T>
where
    A: Alignment,
    T: Debug,
{
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        self.value.fmt(f)
    }
}

impl<A, T> Display for Aligned<A, T>
where
    A: Alignment,
    T: Display,
{
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        self.value.fmt(f)
    }
}

impl<A, T> PartialEq for Aligned<A, T>
where
    A: Alignment,
    T: PartialEq,
{
    fn eq(&self, other: &Self) -> bool {
        self.value == other.value
    }
}

impl<A, T> Eq for Aligned<A, T>
where
    A: Alignment,
    T: Eq,
{
}

impl<A, T> Hash for Aligned<A, T>
where
    A: Alignment,
    T: Hash,
{
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.value.hash(state);
    }
}

impl<A, T> Ord for Aligned<A, T>
where
    A: Alignment,
    T: Ord,
{
    fn cmp(&self, other: &Self) -> Ordering {
        self.value.cmp(&other.value)
    }
}

impl<A, T> PartialOrd for Aligned<A, T>
where
    A: Alignment,
    T: PartialOrd,
{
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        self.value.partial_cmp(&other.value)
    }
}

#[test]
fn sanity() {
    use core::mem;

    let a: Aligned<A1, _> = Aligned([0u8; 3]);
    let x: Aligned<A2, _> = Aligned([0u8; 3]);
    let y: Aligned<A4, _> = Aligned([0u8; 3]);
    let z: Aligned<A8, _> = Aligned([0u8; 3]);
    let w: Aligned<A16, _> = Aligned([0u8; 3]);

    // check alignment
    assert_eq!(mem::align_of_val(&a), 1);
    assert_eq!(mem::align_of_val(&x), 2);
    assert_eq!(mem::align_of_val(&y), 4);
    assert_eq!(mem::align_of_val(&z), 8);
    assert_eq!(mem::align_of_val(&w), 16);

    assert!(a.as_ptr() as usize % 1 == 0);
    assert!(x.as_ptr() as usize % 2 == 0);
    assert!(y.as_ptr() as usize % 4 == 0);
    assert!(z.as_ptr() as usize % 8 == 0);
    assert!(w.as_ptr() as usize % 16 == 0);

    // test `deref`
    assert_eq!(a.len(), 3);
    assert_eq!(x.len(), 3);
    assert_eq!(y.len(), 3);
    assert_eq!(z.len(), 3);
    assert_eq!(w.len(), 3);

    // alignment should be preserved after slicing
    let a: &Aligned<_, [_]> = &a;
    let x: &Aligned<_, [_]> = &x;
    let y: &Aligned<_, [_]> = &y;
    let z: &Aligned<_, [_]> = &z;
    let w: &Aligned<_, [_]> = &w;

    let a: &Aligned<_, _> = &a[..2];
    let x: &Aligned<_, _> = &x[..2];
    let y: &Aligned<_, _> = &y[..2];
    let z: &Aligned<_, _> = &z[..2];
    let w: &Aligned<_, _> = &w[..2];

    assert!(a.as_ptr() as usize % 1 == 0);
    assert!(x.as_ptr() as usize % 2 == 0);
    assert!(y.as_ptr() as usize % 4 == 0);
    assert!(z.as_ptr() as usize % 8 == 0);
    assert!(w.as_ptr() as usize % 16 == 0);

    // alignment should be preserved after boxing
    let a: Box<Aligned<A1, [u8]>> = Box::new(Aligned([0u8; 3]));
    let x: Box<Aligned<A2, [u8]>> = Box::new(Aligned([0u8; 3]));
    let y: Box<Aligned<A4, [u8]>> = Box::new(Aligned([0u8; 3]));
    let z: Box<Aligned<A8, [u8]>> = Box::new(Aligned([0u8; 3]));
    let w: Box<Aligned<A16, [u8]>> = Box::new(Aligned([0u8; 3]));

    assert_eq!(mem::align_of_val(&*a), 1);
    assert_eq!(mem::align_of_val(&*x), 2);
    assert_eq!(mem::align_of_val(&*y), 4);
    assert_eq!(mem::align_of_val(&*z), 8);
    assert_eq!(mem::align_of_val(&*w), 16);

    // test coercions
    let x: Aligned<A2, _> = Aligned([0u8; 3]);
    let y: &Aligned<A2, [u8]> = &x;
    let _: &[u8] = y;
}