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
158

//! This crate provides functions for aligning addresses.
//!
//! [`Align`] is implemented for all unsigned integers and provides methods for:
//! * [`align_down`]
//! * [`align_up`]
//! * [`is_aligned`]
//!
//! [`align_down`]: Align::align_down
//! [`align_up`]: Align::align_up
//! [`is_aligned`]: Align::is_aligned
//!
//! This crate is based on work from the [`x86_64`] crate, but is available for all architectures and all unsigned integer types.
//!
//! [`x86_64`]: https://docs.rs/x86_64
//!
//! # Examples
//!
//! ```
//! use align_address::Align;
//!
//! assert_eq!(123_u64.align_up(2_u64), 124);
//! ```

#![no_std]
#![forbid(unsafe_code)]

/// An adress that can be aligned.
pub trait Align<A>: Copy {
    /// Align address downwards.
    ///
    /// Returns the greatest `x` with alignment `align` so that `x <= addr`.
    ///
    /// Panics if the alignment is not a power of two.
    fn align_down(self, align: A) -> Self;

    /// Align address upwards.
    ///
    /// Returns the smallest `x` with alignment `align` so that `x >= addr`.
    ///
    /// Panics if the alignment is not a power of two or if an overflow occurs.
    fn align_up(self, align: A) -> Self;

    /// Checks whether the address has the demanded alignment.
    fn is_aligned(self, align: A) -> bool;
}

macro_rules! align_impl {
    ($u:ty, $align_down:ident, $align_up:ident) => {
        /// Align address downwards.
        ///
        /// Returns the greatest `x` with alignment `align` so that `x <= addr`.
        ///
        /// Panics if the alignment is not a power of two.
        // Adapted from `x86_64`
        #[inline]
        const fn $align_down(addr: $u, align: $u) -> $u {
            assert!(align.is_power_of_two(), "`align` must be a power of two");
            addr & !(align - 1)
        }

        /// Align address upwards.
        ///
        /// Returns the smallest `x` with alignment `align` so that `x >= addr`.
        ///
        /// Panics if the alignment is not a power of two or if an overflow occurs.
        // Adapted from `x86_64`
        #[inline]
        const fn $align_up(addr: $u, align: $u) -> $u {
            assert!(align.is_power_of_two(), "`align` must be a power of two");
            let align_mask = align - 1;
            if addr & align_mask == 0 {
                addr // already aligned
            } else {
                // FIXME: Replace with .expect, once `Option::expect` is const.
                if let Some(aligned) = (addr | align_mask).checked_add(1) {
                    aligned
                } else {
                    panic!("attempt to add with overflow")
                }
            }
        }

        impl<A: Into<Self>> Align<A> for $u {
            #[inline]
            fn align_down(self, align: A) -> Self {
                $align_down(self, align.into())
            }

            #[inline]
            fn align_up(self, align: A) -> Self {
                $align_up(self, align.into())
            }

            #[inline]
            fn is_aligned(self, align: A) -> bool {
                self.align_down(align) == self
            }
        }
    };
}

align_impl!(u8, align_down_u8, align_up_u8);
align_impl!(u16, align_down_u16, align_up_u16);
align_impl!(u32, align_down_u32, align_up_u32);
align_impl!(u64, align_down_u64, align_up_u64);
align_impl!(u128, align_down_u128, align_up_u128);
align_impl!(usize, align_down_usize, align_up_usize);

// Adapted from `x86_64`
#[cfg(test)]
mod tests {
    use super::*;

    macro_rules! test_align_up_impl {
        ($u:ty, $align_up:ident, $test_align_up:ident) => {
            #[test]
            fn $test_align_up() {
                // align 1
                assert_eq!($align_up(0, 1), 0);
                assert_eq!($align_up(123, 1), 123);
                assert_eq!($align_up(<$u>::MAX, 1), <$u>::MAX);
                // align 2
                assert_eq!($align_up(0, 2), 0);
                assert_eq!($align_up(123, 2), 124);
                assert_eq!($align_up(<$u>::MAX - 1, 2), <$u>::MAX - 1);
                // address 0
                assert_eq!($align_up(0, 128), 0);
                assert_eq!($align_up(0, 1), 0);
                assert_eq!($align_up(0, 2), 0);
                assert_eq!($align_up(0, <$u>::MAX & 1 << (<$u>::BITS - 1)), 0);
            }
        };
    }

    test_align_up_impl!(u8, align_up_u8, test_align_up_u8);
    test_align_up_impl!(u16, align_up_u16, test_align_up_u16);
    test_align_up_impl!(u32, align_up_u32, test_align_up_u32);
    test_align_up_impl!(u64, align_up_u64, test_align_up_u64);
    test_align_up_impl!(u128, align_up_u128, test_align_up_u128);
    test_align_up_impl!(usize, align_up_usize, test_align_up_usize);

    macro_rules! test_align_up_overflow_impl {
        ($u:ty, $test_align_up_overflow:ident, $two:expr) => {
            #[test]
            #[should_panic]
            fn $test_align_up_overflow() {
                <$u>::MAX.align_up($two);
            }
        };
    }

    test_align_up_overflow_impl!(u8, test_align_up_overflow_u8, 2_u8);
    test_align_up_overflow_impl!(u16, test_align_up_overflow_u16, 2_u16);
    test_align_up_overflow_impl!(u32, test_align_up_overflow_u32, 2_u32);
    test_align_up_overflow_impl!(u64, test_align_up_overflow_u64, 2_u64);
    test_align_up_overflow_impl!(u128, test_align_up_overflow_u128, 2_u128);
    test_align_up_overflow_impl!(usize, test_align_up_overflow_usize, 2_usize);
}