aws_lc_rs/
endian.rs

1// Copyright 2015-2021 Brian Smith.
2// SPDX-License-Identifier: ISC
3// Modifications copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
4// SPDX-License-Identifier: Apache-2.0 OR ISC
5
6/// An `Encoding` of a type `T` can be converted to/from its byte
7/// representation without any byte swapping or other computation.
8///
9/// The `Self: Copy` constraint addresses `clippy::declare_interior_mutable_const`.
10pub trait Encoding<T>: From<T> + Into<T>
11where
12    Self: Copy,
13{
14    const ZERO: Self;
15}
16
17use core::mem::size_of_val;
18
19pub fn as_byte_slice<E: Encoding<T>, T>(x: &[E]) -> &[u8] {
20    unsafe { core::slice::from_raw_parts(x.as_ptr().cast::<u8>(), size_of_val(x)) }
21}
22
23/// Work around the inability to implement `AsRef` for arrays of `Encoding`s
24/// due to the coherence rules.
25pub trait ArrayEncoding<T> {
26    fn as_byte_array(&self) -> &T;
27}
28
29/// Work around the inability to implement `from` for arrays of `Encoding`s
30/// due to the coherence rules.
31pub trait FromArray<const N: usize, T>
32where
33    Self: Sized,
34{
35    fn from_array(a: &[T; N]) -> [Self; N];
36}
37
38macro_rules! define_endian {
39    ($endian:ident) => {
40        #[derive(Copy, Clone)]
41        #[repr(transparent)]
42        pub struct $endian<T>(T);
43    };
44}
45
46macro_rules! impl_array_encoding {
47    // This may be converted to use const generics once generic_const_exprs is stable.
48    // https://github.com/rust-lang/rust/issues/76560
49    ($endian:ident, $base:ident, $elems:expr) => {
50        impl ArrayEncoding<[u8; $elems * core::mem::size_of::<$base>()]>
51            for [$endian<$base>; $elems]
52        {
53            fn as_byte_array(&self) -> &[u8; $elems * core::mem::size_of::<$base>()] {
54                as_byte_slice(self).try_into().unwrap()
55            }
56        }
57    };
58}
59
60macro_rules! impl_endian {
61    ($endian:ident, $base:ident, $to_endian:ident, $from_endian:ident, $size:expr) => {
62        impl Encoding<$base> for $endian<$base> {
63            const ZERO: Self = Self(0);
64        }
65
66        impl From<$base> for $endian<$base> {
67            #[inline]
68            fn from(value: $base) -> Self {
69                Self($base::$to_endian(value))
70            }
71        }
72
73        impl From<$endian<$base>> for $base {
74            #[inline]
75            fn from($endian(value): $endian<$base>) -> Self {
76                $base::$from_endian(value)
77            }
78        }
79
80        impl<const N: usize> FromArray<N, $base> for $endian<$base> {
81            fn from_array(value: &[$base; N]) -> [Self; N] {
82                let mut result: [$endian<$base>; N] = [$endian::ZERO; N];
83                for i in 0..N {
84                    result[i] = $endian::from(value[i]);
85                }
86                return result;
87            }
88        }
89
90        impl_array_encoding!($endian, $base, 1);
91        impl_array_encoding!($endian, $base, 2);
92        impl_array_encoding!($endian, $base, 3);
93        impl_array_encoding!($endian, $base, 4);
94        impl_array_encoding!($endian, $base, 8);
95    };
96}
97
98define_endian!(BigEndian);
99define_endian!(LittleEndian);
100impl_endian!(BigEndian, u32, to_be, from_be, 4);
101impl_endian!(BigEndian, u64, to_be, from_be, 8);
102impl_endian!(LittleEndian, u32, to_le, from_le, 4);
103impl_endian!(LittleEndian, u64, to_le, from_le, 8);
104
105#[cfg(test)]
106mod tests {
107    use super::*;
108
109    #[test]
110    fn test_big_endian() {
111        let x = BigEndian::from(1u32);
112        let x2 = x;
113        assert_eq!(u32::from(x), 1);
114        assert_eq!(u32::from(x2), 1);
115    }
116
117    #[test]
118    fn test_endian_from_array() {
119        let be: [BigEndian<u32>; 2] =
120            BigEndian::<u32>::from_array(&[0x_AABB_CCDD_u32, 0x_2233_4455_u32]);
121        let le: [LittleEndian<u32>; 2] =
122            LittleEndian::<u32>::from_array(&[0x_DDCC_BBAA_u32, 0x_5544_3322_u32]);
123        assert_eq!(be.as_byte_array(), le.as_byte_array());
124
125        let be: [BigEndian<u64>; 2] =
126            BigEndian::<u64>::from_array(&[0x_AABB_CCDD_EEFF_0011_u64, 0x_2233_4455_6677_8899_u64]);
127        let le: [LittleEndian<u64>; 2] = LittleEndian::<u64>::from_array(&[
128            0x_1100_FFEE_DDCC_BBAA_u64,
129            0x_9988_7766_5544_3322_u64,
130        ]);
131        assert_eq!(be.as_byte_array(), le.as_byte_array());
132    }
133}
aws_lc_rs/endian.rs

aws_lc_rs/
endian.rs
