aligned 0.3.1

A newtype with alignment of at least `A` bytes
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157

//! 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::ops;

use as_slice::{AsMutSlice, AsSlice};

mod sealed;

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

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

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

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

/// A newtype with alignment of at least `A` bytes
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: sealed::Alignment,
    T: ?Sized,
{
    type Target = T;

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

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

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

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

    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(&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!(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!(x.len(), 3);
    assert_eq!(y.len(), 3);
    assert_eq!(z.len(), 3);
    assert_eq!(w.len(), 3);

    // alignment should be preserved after boxing
    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(&*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 deref-ing
    let x: Aligned<A2, _> = Aligned([0u8; 3]);
    let y: &Aligned<A2, [u8]> = &x;
    let _: &[u8] = y;
}