dsi_bitstream/traits/
endianness.rs

1/*
2 * SPDX-FileCopyrightText: 2023 Tommaso Fontana
3 * SPDX-FileCopyrightText: 2023 Inria
4 * SPDX-FileCopyrightText: 2023 Sebastiano Vigna
5 *
6 * SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
7 */
8
9/// Inner private trait used to make implementing [`Endianness`]
10/// impossible for other structs.
11mod private {
12    /// This is a [SealedTrait](https://predr.ag/blog/definitive-guide-to-sealed-traits-in-rust/).
13    pub trait Endianness: 'static + Send + Sync + Copy {
14        /// The name of the endianness.
15        const _NAME: &'static str;
16        /// Whether the endianness is little-endian.
17        const _IS_LITTLE: bool;
18        /// Whether the endianness is big-endian.
19        const _IS_BIG: bool;
20    }
21}
22
23impl<T: private::Endianness> Endianness for T {
24    const NAME: &'static str = T::_NAME;
25    const IS_LITTLE: bool = T::_IS_LITTLE;
26    const IS_BIG: bool = T::_IS_BIG;
27}
28
29/// Marker trait for endianness selector types.
30///
31/// Its only implementations are [`LittleEndian`] and [`BigEndian`].
32///
33/// Note that in principle marker traits are not necessary to use selector
34/// types, but they are useful to prevent the user from specifying a nonsensical
35/// type, and to document the meaning of type parameters.
36pub trait Endianness: private::Endianness {
37    /// The name of the endianness.
38    const NAME: &'static str;
39    /// Whether the endianness is little-endian.
40    const IS_LITTLE: bool;
41    /// Whether the endianness is big-endian.
42    const IS_BIG: bool;
43}
44
45impl core::fmt::Display for LE {
46    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
47        f.write_str(LE::NAME)
48    }
49}
50
51impl core::fmt::Display for BE {
52    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
53        f.write_str(BE::NAME)
54    }
55}
56
57/// Selector type for little-endian streams.
58#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
59pub struct LittleEndian;
60
61/// Selector type for big-endian streams.
62#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
63pub struct BigEndian;
64
65impl private::Endianness for LittleEndian {
66    const _NAME: &'static str = "little";
67    const _IS_LITTLE: bool = true;
68    const _IS_BIG: bool = false;
69}
70
71impl private::Endianness for BigEndian {
72    const _NAME: &'static str = "big";
73    const _IS_LITTLE: bool = false;
74    const _IS_BIG: bool = true;
75}
76
77/// Alias for [`BigEndian`].
78pub type BE = BigEndian;
79
80/// Alias for [`LittleEndian`].
81pub type LE = LittleEndian;
82
83#[cfg(target_endian = "little")]
84/// A type alias for the native endianness of the target platform.
85pub type NativeEndian = LittleEndian;
86#[cfg(target_endian = "big")]
87/// A type alias for the native endianness of the target platform.
88pub type NativeEndian = BigEndian;
89
90/// Alias for [`NativeEndian`].
91pub type NE = NativeEndian;
dsi_bitstream/traits/endianness.rs

dsi_bitstream/traits/
endianness.rs
