src/byteorder.rs - platform/external/rust/crates/zerocopy - Git at Google

 // Copyright 2019 The Fuchsia Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 //! Byte order-aware numeric primitives.
 //!
 //! This module contains equivalents of the native multi-byte integer types with
 //! no alignment requirement and supporting byte order conversions.
 //!
 //! For each native multi-byte integer type - `u16`, `i16`, `u32`, etc - an
 //! equivalent type is defined by this module - [`U16`], [`I16`], [`U32`], etc.
 //! Unlike their native counterparts, these types have alignment 1, and take a
 //! type parameter specifying the byte order in which the bytes are stored in
 //! memory. Each type implements the [`FromBytes`], [`AsBytes`], and
 //! [`Unaligned`] traits.
 //!
 //! These two properties, taken together, make these types very useful for
 //! defining data structures whose memory layout matches a wire format such as
 //! that of a network protocol or a file format. Such formats often have
 //! multi-byte values at offsets that do not respect the alignment requirements
 //! of the equivalent native types, and stored in a byte order not necessarily
 //! the same as that of the target platform.
 //!
 //! # Example
 //!
 //! One use of these types is for representing network packet formats, such as
 //! UDP:
 //!
 //! ```edition2018
 //! # use zerocopy::*;
 //! use ::byteorder::NetworkEndian;
 //!
 //! #[derive(FromBytes, AsBytes, Unaligned)]
 //! #[repr(C)]
 //! struct UdpHeader {
 //!     src_port: U16<NetworkEndian>,
 //!     dst_port: U16<NetworkEndian>,
 //!     length: U16<NetworkEndian>,
 //!     checksum: U16<NetworkEndian>,
 //! }
 //!
 //! struct UdpPacket<B: ByteSlice> {
 //!     header: LayoutVerified<B, UdpHeader>,
 //!     body: B,
 //! }
 //!
 //! impl<B: ByteSlice> UdpPacket<B> {
 //!     fn parse(bytes: B) -> Option<UdpPacket<B>> {
 //!         let (header, body) = LayoutVerified::new_from_prefix(bytes)?;
 //!         Some(UdpPacket { header, body })
 //!     }
 //!
 //!     fn src_port(&self) -> u16 {
 //!         self.header.src_port.get()
 //!     }
 //!
 //!     // more getters...
 //! }
 //! ```

 use core::convert::{TryFrom, TryInto};
 use core::fmt::{self, Binary, Debug, Display, Formatter, LowerHex, Octal, UpperHex};
 use core::marker::PhantomData;
 use core::num::TryFromIntError;

 use zerocopy_derive::*;

 use crate::AsBytes;
 // This allows the custom derives to work. See the comment on this module for an
 // explanation.
 use crate::zerocopy;

 // NOTE: We don't reexport `WriteBytesExt` or `ReadBytesExt` because those are
 // only available with the `std` feature enabled, and zerocopy is `no_std` by
 // default.
 pub use byteorder::{BigEndian, ByteOrder, LittleEndian, NativeEndian, NetworkEndian, BE, LE};

 macro_rules! impl_fmt_trait {
     ($name:ident, $native:ident, $trait:ident) => {
         impl<O: ByteOrder> $trait for $name<O> {
             fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
                 $trait::fmt(&self.get(), f)
             }
         }
     };
 }

 macro_rules! doc_comment {
     ($x:expr, $($tt:tt)*) => {
         #[doc = $x]
         $($tt)*
     };
 }

 macro_rules! define_max_value_constant {
     ($name:ident, $bytes:expr, unsigned) => {
         /// The maximum value.
         ///
         /// This constant should be preferred to constructing a new value using
         /// `new`, as `new` may perform an endianness swap depending on the
         /// endianness `O` and the endianness of the platform.
         pub const MAX_VALUE: $name<O> = $name([0xFFu8; $bytes], PhantomData);
     };
     ($name:ident, $bytes:expr, signed) => {
         // We don't provide maximum and minimum value constants for signed
         // values because there's no way to do it generically - it would require
         // a different value depending on the value of the ByteOrder type
         // parameter. Currently, one workaround would be to provide
         // implementations for concrete implementations of that trait. In the
         // long term, if we are ever able to make the `new` constructor a const
         // fn, we could use that instead.
     };
 }

 macro_rules! define_type {
     ($article:ident,
         $name:ident,
         $native:ident,
         $bits:expr,
         $bytes:expr,
         $read_method:ident,
         $write_method:ident,
         $sign:ident,
         [$($larger_native:ty),*],
         [$($larger_byteorder:ident),*]) => {
         doc_comment! {
             concat!("A ", stringify!($bits), "-bit ", stringify!($sign), " integer
 stored in `O` byte order.

 `", stringify!($name), "` is like the native `", stringify!($native), "` type with
 two major differences: First, it has no alignment requirement (its alignment is 1).
 Second, the endianness of its memory layout is given by the type parameter `O`.

 ", stringify!($article), " `", stringify!($name), "` can be constructed using
 the [`new`] method, and its contained value can be obtained as a native
 `",stringify!($native), "` using the [`get`] method, or updated in place with
 the [`set`] method. In all cases, if the endianness `O` is not the same as the
 endianness of the current platform, an endianness swap will be performed in
 order to uphold the invariants that a) the layout of `", stringify!($name), "`
 has endianness `O` and that, b) the layout of `", stringify!($native), "` has
 the platform's native endianness.

 `", stringify!($name), "` implements [`FromBytes`], [`AsBytes`], and [`Unaligned`],
 making it useful for parsing and serialization. See the module documentation for an
 example of how it can be used for parsing UDP packets.

 [`new`]: crate::byteorder::", stringify!($name), "::new
 [`get`]: crate::byteorder::", stringify!($name), "::get
 [`set`]: crate::byteorder::", stringify!($name), "::set
 [`FromBytes`]: crate::FromBytes
 [`AsBytes`]: crate::AsBytes
 [`Unaligned`]: crate::Unaligned"),
             #[derive(FromBytes, Unaligned, Copy, Clone, Eq, PartialEq, Hash)]
             #[repr(transparent)]
             pub struct $name<O>([u8; $bytes], PhantomData<O>);
         }

         impl<O> Default for $name<O> {
             fn default() -> $name<O> {
                 $name::ZERO
             }
         }

         // TODO(joshlf): Replace this with #[derive(AsBytes)] once that derive
         // supports type parameters.
         unsafe impl<O: ByteOrder> AsBytes for $name<O> {
             fn only_derive_is_allowed_to_implement_this_trait()
             where
                 Self: Sized,
             {
             }
         }

         impl<O> $name<O> {
             /// The value zero.
             ///
             /// This constant should be preferred to constructing a new value
             /// using `new`, as `new` may perform an endianness swap depending
             /// on the endianness and platform.
             pub const ZERO: $name<O> = $name([0u8; $bytes], PhantomData);

             define_max_value_constant!($name, $bytes, $sign);

             /// Constructs a new value from bytes which are already in the
             /// endianness `O`.
             pub const fn from_bytes(bytes: [u8; $bytes]) -> $name<O> {
                 $name(bytes, PhantomData)
             }
         }

         impl<O: ByteOrder> $name<O> {
             // TODO(joshlf): Make these const fns if the ByteOrder methods ever
             // become const fns.

             /// Constructs a new value, possibly performing an endianness swap
             /// to guarantee that the returned value has endianness `O`.
             pub fn new(n: $native) -> $name<O> {
                 let mut out = $name::default();
                 O::$write_method(&mut out.0[..], n);
                 out
             }

             /// Returns the value as a primitive type, possibly performing an
             /// endianness swap to guarantee that the return value has the
             /// endianness of the native platform.
             pub fn get(self) -> $native {
                 O::$read_method(&self.0[..])
             }

             /// Updates the value in place as a primitive type, possibly
             /// performing an endianness swap to guarantee that the stored value
             /// has the endianness `O`.
             pub fn set(&mut self, n: $native) {
                 O::$write_method(&mut self.0[..], n);
             }
         }

         // NOTE: The reasoning behind which traits to implement here is to only
         // implement traits which won't cause inference issues. Notably,
         // comparison traits like PartialEq and PartialOrd tend to cause
         // inference issues.

         impl<O: ByteOrder> From<$name<O>> for [u8; $bytes] {
             fn from(x: $name<O>) -> [u8; $bytes] {
                 x.0
             }
         }

         impl<O: ByteOrder> From<[u8; $bytes]> for $name<O> {
             fn from(bytes: [u8; $bytes]) -> $name<O> {
                 $name(bytes, PhantomData)
             }
         }

         impl<O: ByteOrder> From<$name<O>> for $native {
             fn from(x: $name<O>) -> $native {
                 x.get()
             }
         }

         impl<O: ByteOrder> From<$native> for $name<O> {
             fn from(x: $native) -> $name<O> {
                 $name::new(x)
             }
         }

         $(
             impl<O: ByteOrder> From<$name<O>> for $larger_native {
                 fn from(x: $name<O>) -> $larger_native {
                     x.get().into()
                 }
             }

             impl<O: ByteOrder> TryFrom<$larger_native> for $name<O> {
                 type Error = TryFromIntError;
                 fn try_from(x: $larger_native) -> Result<$name<O>, TryFromIntError> {
                     $native::try_from(x).map($name::new)
                 }
             }
         )*

         $(
             impl<O: ByteOrder, P: ByteOrder> From<$name<O>> for $larger_byteorder<P> {
                 fn from(x: $name<O>) -> $larger_byteorder<P> {
                     $larger_byteorder::new(x.get().into())
                 }
             }

             impl<O: ByteOrder, P: ByteOrder> TryFrom<$larger_byteorder<P>> for $name<O> {
                 type Error = TryFromIntError;
                 fn try_from(x: $larger_byteorder<P>) -> Result<$name<O>, TryFromIntError> {
                     x.get().try_into().map($name::new)
                 }
             }
         )*

         impl<O: ByteOrder> AsRef<[u8; $bytes]> for $name<O> {
             fn as_ref(&self) -> &[u8; $bytes] {
                 &self.0
             }
         }

         impl<O: ByteOrder> AsMut<[u8; $bytes]> for $name<O> {
             fn as_mut(&mut self) -> &mut [u8; $bytes] {
                 &mut self.0
             }
         }

         impl<O: ByteOrder> PartialEq<$name<O>> for [u8; $bytes] {
             fn eq(&self, other: &$name<O>) -> bool {
                 self.eq(&other.0)
             }
         }

         impl<O: ByteOrder> PartialEq<[u8; $bytes]> for $name<O> {
             fn eq(&self, other: &[u8; $bytes]) -> bool {
                 self.0.eq(other)
             }
         }

         impl_fmt_trait!($name, $native, Display);
         impl_fmt_trait!($name, $native, Octal);
         impl_fmt_trait!($name, $native, LowerHex);
         impl_fmt_trait!($name, $native, UpperHex);
         impl_fmt_trait!($name, $native, Binary);

         impl<O: ByteOrder> Debug for $name<O> {
             fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
                 // This results in a format like "U16(42)"
                 write!(f, concat!(stringify!($name), "({})"), self.get())
             }
         }
     };
 }

 define_type!(
     A,
     U16,
     u16,
     16,
     2,
     read_u16,
     write_u16,
     unsigned,
     [u32, u64, u128, usize],
     [U32, U64, U128]
 );
 define_type!(A, U32, u32, 32, 4, read_u32, write_u32, unsigned, [u64, u128], [U64, U128]);
 define_type!(A, U64, u64, 64, 8, read_u64, write_u64, unsigned, [u128], [U128]);
 define_type!(A, U128, u128, 128, 16, read_u128, write_u128, unsigned, [], []);
 define_type!(
     An,
     I16,
     i16,
     16,
     2,
     read_i16,
     write_i16,
     signed,
     [i32, i64, i128, isize],
     [I32, I64, I128]
 );
 define_type!(An, I32, i32, 32, 4, read_i32, write_i32, signed, [i64, i128], [I64, I128]);
 define_type!(An, I64, i64, 64, 8, read_i64, write_i64, signed, [i128], [I128]);
 define_type!(An, I128, i128, 128, 16, read_i128, write_i128, signed, [], []);

 #[cfg(test)]
 mod tests {
     use byteorder::NativeEndian;

     use super::*;
     use crate::{AsBytes, FromBytes, Unaligned};

     // A native integer type (u16, i32, etc)
     trait Native: FromBytes + AsBytes + Copy + Eq + Debug {
         const ZERO: Self;
         const MAX_VALUE: Self;

         fn rand() -> Self;
     }

     trait ByteArray:
         FromBytes + AsBytes + Copy + AsRef<[u8]> + AsMut<[u8]> + Debug + Default + Eq
     {
         /// Invert the order of the bytes in the array.
         fn invert(self) -> Self;
     }

     trait ByteOrderType: FromBytes + AsBytes + Unaligned + Copy + Eq + Debug {
         type Native: Native;
         type ByteArray: ByteArray;

         const ZERO: Self;

         fn new(native: Self::Native) -> Self;
         fn get(self) -> Self::Native;
         fn set(&mut self, native: Self::Native);
         fn from_bytes(bytes: Self::ByteArray) -> Self;
         fn into_bytes(self) -> Self::ByteArray;
     }

     trait ByteOrderTypeUnsigned: ByteOrderType {
         const MAX_VALUE: Self;
     }

     macro_rules! impl_byte_array {
         ($bytes:expr) => {
             impl ByteArray for [u8; $bytes] {
                 fn invert(mut self) -> [u8; $bytes] {
                     self.reverse();
                     self
                 }
             }
         };
     }

     impl_byte_array!(2);
     impl_byte_array!(4);
     impl_byte_array!(8);
     impl_byte_array!(16);

     macro_rules! impl_byte_order_type_unsigned {
         ($name:ident, unsigned) => {
             impl<O: ByteOrder> ByteOrderTypeUnsigned for $name<O> {
                 const MAX_VALUE: $name<O> = $name::MAX_VALUE;
             }
         };
         ($name:ident, signed) => {};
     }

     macro_rules! impl_traits {
         ($name:ident, $native:ident, $bytes:expr, $sign:ident) => {
             impl Native for $native {
                 const ZERO: $native = 0;
                 const MAX_VALUE: $native = ::core::$native::MAX;

                 fn rand() -> $native {
                     rand::random()
                 }
             }

             impl<O: ByteOrder> ByteOrderType for $name<O> {
                 type Native = $native;
                 type ByteArray = [u8; $bytes];

                 const ZERO: $name<O> = $name::ZERO;

                 fn new(native: $native) -> $name<O> {
                     $name::new(native)
                 }

                 fn get(self) -> $native {
                     $name::get(self)
                 }

                 fn set(&mut self, native: $native) {
                     $name::set(self, native)
                 }

                 fn from_bytes(bytes: [u8; $bytes]) -> $name<O> {
                     $name::from(bytes)
                 }

                 fn into_bytes(self) -> [u8; $bytes] {
                     <[u8; $bytes]>::from(self)
                 }
             }

             impl_byte_order_type_unsigned!($name, $sign);
         };
     }

     impl_traits!(U16, u16, 2, unsigned);
     impl_traits!(U32, u32, 4, unsigned);
     impl_traits!(U64, u64, 8, unsigned);
     impl_traits!(U128, u128, 16, unsigned);
     impl_traits!(I16, i16, 2, signed);
     impl_traits!(I32, i32, 4, signed);
     impl_traits!(I64, i64, 8, signed);
     impl_traits!(I128, i128, 16, signed);

     macro_rules! call_for_all_types {
         ($fn:ident, $byteorder:ident) => {
             $fn::<U16<$byteorder>>();
             $fn::<U32<$byteorder>>();
             $fn::<U64<$byteorder>>();
             $fn::<U128<$byteorder>>();
             $fn::<I16<$byteorder>>();
             $fn::<I32<$byteorder>>();
             $fn::<I64<$byteorder>>();
             $fn::<I128<$byteorder>>();
         };
     }

     macro_rules! call_for_unsigned_types {
         ($fn:ident, $byteorder:ident) => {
             $fn::<U16<$byteorder>>();
             $fn::<U32<$byteorder>>();
             $fn::<U64<$byteorder>>();
             $fn::<U128<$byteorder>>();
         };
     }

     #[cfg(target_endian = "big")]
     type NonNativeEndian = byteorder::LittleEndian;
     #[cfg(target_endian = "little")]
     type NonNativeEndian = byteorder::BigEndian;

     #[test]
     fn test_zero() {
         fn test_zero<T: ByteOrderType>() {
             assert_eq!(T::ZERO.get(), T::Native::ZERO);
         }

         call_for_all_types!(test_zero, NativeEndian);
         call_for_all_types!(test_zero, NonNativeEndian);
     }

     #[test]
     fn test_max_value() {
         fn test_max_value<T: ByteOrderTypeUnsigned>() {
             assert_eq!(T::MAX_VALUE.get(), T::Native::MAX_VALUE);
         }

         call_for_unsigned_types!(test_max_value, NativeEndian);
         call_for_unsigned_types!(test_max_value, NonNativeEndian);
     }

     #[test]
     fn test_native_endian() {
         fn test_native_endian<T: ByteOrderType>() {
             for _ in 0..1024 {
                 let native = T::Native::rand();
                 let mut bytes = T::ByteArray::default();
                 bytes.as_bytes_mut().copy_from_slice(native.as_bytes());
                 let mut from_native = T::new(native);
                 let from_bytes = T::from_bytes(bytes);
                 assert_eq!(from_native, from_bytes);
                 assert_eq!(from_native.get(), native);
                 assert_eq!(from_bytes.get(), native);
                 assert_eq!(from_native.into_bytes(), bytes);
                 assert_eq!(from_bytes.into_bytes(), bytes);

                 let updated = T::Native::rand();
                 from_native.set(updated);
                 assert_eq!(from_native.get(), updated);
             }
         }

         call_for_all_types!(test_native_endian, NativeEndian);
     }

     #[test]
     fn test_non_native_endian() {
         fn test_non_native_endian<T: ByteOrderType>() {
             for _ in 0..1024 {
                 let native = T::Native::rand();
                 let mut bytes = T::ByteArray::default();
                 bytes.as_bytes_mut().copy_from_slice(native.as_bytes());
                 bytes = bytes.invert();
                 let mut from_native = T::new(native);
                 let from_bytes = T::from_bytes(bytes);
                 assert_eq!(from_native, from_bytes);
                 assert_eq!(from_native.get(), native);
                 assert_eq!(from_bytes.get(), native);
                 assert_eq!(from_native.into_bytes(), bytes);
                 assert_eq!(from_bytes.into_bytes(), bytes);

                 let updated = T::Native::rand();
                 from_native.set(updated);
                 assert_eq!(from_native.get(), updated);
             }
         }

         call_for_all_types!(test_non_native_endian, NonNativeEndian);
     }
 }
	// Copyright 2019 The Fuchsia Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	//! Byte order-aware numeric primitives.
	//!
	//! This module contains equivalents of the native multi-byte integer types with
	//! no alignment requirement and supporting byte order conversions.
	//!
	//! For each native multi-byte integer type - `u16`, `i16`, `u32`, etc - an
	//! equivalent type is defined by this module - [`U16`], [`I16`], [`U32`], etc.
	//! Unlike their native counterparts, these types have alignment 1, and take a
	//! type parameter specifying the byte order in which the bytes are stored in
	//! memory. Each type implements the [`FromBytes`], [`AsBytes`], and
	//! [`Unaligned`] traits.
	//!
	//! These two properties, taken together, make these types very useful for
	//! defining data structures whose memory layout matches a wire format such as
	//! that of a network protocol or a file format. Such formats often have
	//! multi-byte values at offsets that do not respect the alignment requirements
	//! of the equivalent native types, and stored in a byte order not necessarily
	//! the same as that of the target platform.
	//!
	//! # Example
	//!
	//! One use of these types is for representing network packet formats, such as
	//! UDP:
	//!
	//! ```edition2018
	//! # use zerocopy::*;
	//! use ::byteorder::NetworkEndian;
	//!
	//! #[derive(FromBytes, AsBytes, Unaligned)]
	//! #[repr(C)]
	//! struct UdpHeader {
	//! src_port: U16<NetworkEndian>,
	//! dst_port: U16<NetworkEndian>,
	//! length: U16<NetworkEndian>,
	//! checksum: U16<NetworkEndian>,
	//! }
	//!
	//! struct UdpPacket<B: ByteSlice> {
	//! header: LayoutVerified<B, UdpHeader>,
	//! body: B,
	//! }
	//!
	//! impl<B: ByteSlice> UdpPacket<B> {
	//! fn parse(bytes: B) -> Option<UdpPacket<B>> {
	//! let (header, body) = LayoutVerified::new_from_prefix(bytes)?;
	//! Some(UdpPacket { header, body })
	//! }
	//!
	//! fn src_port(&self) -> u16 {
	//! self.header.src_port.get()
	//! }
	//!
	//! // more getters...
	//! }
	//! ```

	use core::convert::{TryFrom, TryInto};
	use core::fmt::{self, Binary, Debug, Display, Formatter, LowerHex, Octal, UpperHex};
	use core::marker::PhantomData;
	use core::num::TryFromIntError;

	use zerocopy_derive::*;

	use crate::AsBytes;
	// This allows the custom derives to work. See the comment on this module for an
	// explanation.
	use crate::zerocopy;

	// NOTE: We don't reexport `WriteBytesExt` or `ReadBytesExt` because those are
	// only available with the `std` feature enabled, and zerocopy is `no_std` by
	// default.
	pub use byteorder::{BigEndian, ByteOrder, LittleEndian, NativeEndian, NetworkEndian, BE, LE};

	macro_rules! impl_fmt_trait {
	($name:ident, $native:ident, $trait:ident) => {
	impl<O: ByteOrder> $trait for $name<O> {
	fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
	$trait::fmt(&self.get(), f)
	}
	}
	};
	}

	macro_rules! doc_comment {
	($x:expr, $($tt:tt)*) => {
	#[doc = $x]
	$($tt)*
	};
	}

	macro_rules! define_max_value_constant {
	($name:ident, $bytes:expr, unsigned) => {
	/// The maximum value.
	///
	/// This constant should be preferred to constructing a new value using
	/// `new`, as `new` may perform an endianness swap depending on the
	/// endianness `O` and the endianness of the platform.
	pub const MAX_VALUE: $name<O> = $name([0xFFu8; $bytes], PhantomData);
	};
	($name:ident, $bytes:expr, signed) => {
	// We don't provide maximum and minimum value constants for signed
	// values because there's no way to do it generically - it would require
	// a different value depending on the value of the ByteOrder type
	// parameter. Currently, one workaround would be to provide
	// implementations for concrete implementations of that trait. In the
	// long term, if we are ever able to make the `new` constructor a const
	// fn, we could use that instead.
	};
	}

	macro_rules! define_type {
	($article:ident,
	$name:ident,
	$native:ident,
	$bits:expr,
	$bytes:expr,
	$read_method:ident,
	$write_method:ident,
	$sign:ident,
	[$($larger_native:ty),*],
	[$($larger_byteorder:ident),*]) => {
	doc_comment! {
	concat!("A ", stringify!($bits), "-bit ", stringify!($sign), " integer
	stored in `O` byte order.

	`", stringify!($name), "` is like the native `", stringify!($native), "` type with
	two major differences: First, it has no alignment requirement (its alignment is 1).
	Second, the endianness of its memory layout is given by the type parameter `O`.

	", stringify!($article), " `", stringify!($name), "` can be constructed using
	the [`new`] method, and its contained value can be obtained as a native
	`",stringify!($native), "` using the [`get`] method, or updated in place with
	the [`set`] method. In all cases, if the endianness `O` is not the same as the
	endianness of the current platform, an endianness swap will be performed in
	order to uphold the invariants that a) the layout of `", stringify!($name), "`
	has endianness `O` and that, b) the layout of `", stringify!($native), "` has
	the platform's native endianness.

	`", stringify!($name), "` implements [`FromBytes`], [`AsBytes`], and [`Unaligned`],
	making it useful for parsing and serialization. See the module documentation for an
	example of how it can be used for parsing UDP packets.

	[`new`]: crate::byteorder::", stringify!($name), "::new
	[`get`]: crate::byteorder::", stringify!($name), "::get
	[`set`]: crate::byteorder::", stringify!($name), "::set
	[`FromBytes`]: crate::FromBytes
	[`AsBytes`]: crate::AsBytes
	[`Unaligned`]: crate::Unaligned"),
	#[derive(FromBytes, Unaligned, Copy, Clone, Eq, PartialEq, Hash)]
	#[repr(transparent)]
	pub struct $name<O>([u8; $bytes], PhantomData<O>);
	}

	impl<O> Default for $name<O> {
	fn default() -> $name<O> {
	$name::ZERO
	}
	}

	// TODO(joshlf): Replace this with #[derive(AsBytes)] once that derive
	// supports type parameters.
	unsafe impl<O: ByteOrder> AsBytes for $name<O> {
	fn only_derive_is_allowed_to_implement_this_trait()
	where
	Self: Sized,
	{
	}
	}

	impl<O> $name<O> {
	/// The value zero.
	///
	/// This constant should be preferred to constructing a new value
	/// using `new`, as `new` may perform an endianness swap depending
	/// on the endianness and platform.
	pub const ZERO: $name<O> = $name([0u8; $bytes], PhantomData);

	define_max_value_constant!($name, $bytes, $sign);

	/// Constructs a new value from bytes which are already in the
	/// endianness `O`.
	pub const fn from_bytes(bytes: [u8; $bytes]) -> $name<O> {
	$name(bytes, PhantomData)
	}
	}

	impl<O: ByteOrder> $name<O> {
	// TODO(joshlf): Make these const fns if the ByteOrder methods ever
	// become const fns.

	/// Constructs a new value, possibly performing an endianness swap
	/// to guarantee that the returned value has endianness `O`.
	pub fn new(n: $native) -> $name<O> {
	let mut out = $name::default();
	O::$write_method(&mut out.0[..], n);
	out
	}

	/// Returns the value as a primitive type, possibly performing an
	/// endianness swap to guarantee that the return value has the
	/// endianness of the native platform.
	pub fn get(self) -> $native {
	O::$read_method(&self.0[..])
	}

	/// Updates the value in place as a primitive type, possibly
	/// performing an endianness swap to guarantee that the stored value
	/// has the endianness `O`.
	pub fn set(&mut self, n: $native) {
	O::$write_method(&mut self.0[..], n);
	}
	}

	// NOTE: The reasoning behind which traits to implement here is to only
	// implement traits which won't cause inference issues. Notably,
	// comparison traits like PartialEq and PartialOrd tend to cause
	// inference issues.

	impl<O: ByteOrder> From<$name<O>> for [u8; $bytes] {
	fn from(x: $name<O>) -> [u8; $bytes] {
	x.0
	}
	}

	impl<O: ByteOrder> From<[u8; $bytes]> for $name<O> {
	fn from(bytes: [u8; $bytes]) -> $name<O> {
	$name(bytes, PhantomData)
	}
	}

	impl<O: ByteOrder> From<$name<O>> for $native {
	fn from(x: $name<O>) -> $native {
	x.get()
	}
	}

	impl<O: ByteOrder> From<$native> for $name<O> {
	fn from(x: $native) -> $name<O> {
	$name::new(x)
	}
	}

	$(
	impl<O: ByteOrder> From<$name<O>> for $larger_native {
	fn from(x: $name<O>) -> $larger_native {
	x.get().into()
	}
	}

	impl<O: ByteOrder> TryFrom<$larger_native> for $name<O> {
	type Error = TryFromIntError;
	fn try_from(x: $larger_native) -> Result<$name<O>, TryFromIntError> {
	$native::try_from(x).map($name::new)
	}
	}
	)*

	$(
	impl<O: ByteOrder, P: ByteOrder> From<$name<O>> for $larger_byteorder<P> {
	fn from(x: $name<O>) -> $larger_byteorder<P> {
	$larger_byteorder::new(x.get().into())
	}
	}

	impl<O: ByteOrder, P: ByteOrder> TryFrom<$larger_byteorder<P>> for $name<O> {
	type Error = TryFromIntError;
	fn try_from(x: $larger_byteorder<P>) -> Result<$name<O>, TryFromIntError> {
	x.get().try_into().map($name::new)
	}
	}
	)*

	impl<O: ByteOrder> AsRef<[u8; $bytes]> for $name<O> {
	fn as_ref(&self) -> &[u8; $bytes] {
	&self.0
	}
	}

	impl<O: ByteOrder> AsMut<[u8; $bytes]> for $name<O> {
	fn as_mut(&mut self) -> &mut [u8; $bytes] {
	&mut self.0
	}
	}

	impl<O: ByteOrder> PartialEq<$name<O>> for [u8; $bytes] {
	fn eq(&self, other: &$name<O>) -> bool {
	self.eq(&other.0)
	}
	}

	impl<O: ByteOrder> PartialEq<[u8; $bytes]> for $name<O> {
	fn eq(&self, other: &[u8; $bytes]) -> bool {
	self.0.eq(other)
	}
	}

	impl_fmt_trait!($name, $native, Display);
	impl_fmt_trait!($name, $native, Octal);
	impl_fmt_trait!($name, $native, LowerHex);
	impl_fmt_trait!($name, $native, UpperHex);
	impl_fmt_trait!($name, $native, Binary);

	impl<O: ByteOrder> Debug for $name<O> {
	fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
	// This results in a format like "U16(42)"
	write!(f, concat!(stringify!($name), "({})"), self.get())
	}
	}
	};
	}

	define_type!(
	A,
	U16,
	u16,
	16,
	2,
	read_u16,
	write_u16,
	unsigned,
	[u32, u64, u128, usize],
	[U32, U64, U128]
	);
	define_type!(A, U32, u32, 32, 4, read_u32, write_u32, unsigned, [u64, u128], [U64, U128]);
	define_type!(A, U64, u64, 64, 8, read_u64, write_u64, unsigned, [u128], [U128]);
	define_type!(A, U128, u128, 128, 16, read_u128, write_u128, unsigned, [], []);
	define_type!(
	An,
	I16,
	i16,
	16,
	2,
	read_i16,
	write_i16,
	signed,
	[i32, i64, i128, isize],
	[I32, I64, I128]
	);
	define_type!(An, I32, i32, 32, 4, read_i32, write_i32, signed, [i64, i128], [I64, I128]);
	define_type!(An, I64, i64, 64, 8, read_i64, write_i64, signed, [i128], [I128]);
	define_type!(An, I128, i128, 128, 16, read_i128, write_i128, signed, [], []);

	#[cfg(test)]
	mod tests {
	use byteorder::NativeEndian;

	use super::*;
	use crate::{AsBytes, FromBytes, Unaligned};

	// A native integer type (u16, i32, etc)
	trait Native: FromBytes + AsBytes + Copy + Eq + Debug {
	const ZERO: Self;
	const MAX_VALUE: Self;

	fn rand() -> Self;
	}

	trait ByteArray:
	FromBytes + AsBytes + Copy + AsRef<[u8]> + AsMut<[u8]> + Debug + Default + Eq
	{
	/// Invert the order of the bytes in the array.
	fn invert(self) -> Self;
	}

	trait ByteOrderType: FromBytes + AsBytes + Unaligned + Copy + Eq + Debug {
	type Native: Native;
	type ByteArray: ByteArray;

	const ZERO: Self;

	fn new(native: Self::Native) -> Self;
	fn get(self) -> Self::Native;
	fn set(&mut self, native: Self::Native);
	fn from_bytes(bytes: Self::ByteArray) -> Self;
	fn into_bytes(self) -> Self::ByteArray;
	}

	trait ByteOrderTypeUnsigned: ByteOrderType {
	const MAX_VALUE: Self;
	}

	macro_rules! impl_byte_array {
	($bytes:expr) => {
	impl ByteArray for [u8; $bytes] {
	fn invert(mut self) -> [u8; $bytes] {
	self.reverse();
	self
	}
	}
	};
	}

	impl_byte_array!(2);
	impl_byte_array!(4);
	impl_byte_array!(8);
	impl_byte_array!(16);

	macro_rules! impl_byte_order_type_unsigned {
	($name:ident, unsigned) => {
	impl<O: ByteOrder> ByteOrderTypeUnsigned for $name<O> {
	const MAX_VALUE: $name<O> = $name::MAX_VALUE;
	}
	};
	($name:ident, signed) => {};
	}

	macro_rules! impl_traits {
	($name:ident, $native:ident, $bytes:expr, $sign:ident) => {
	impl Native for $native {
	const ZERO: $native = 0;
	const MAX_VALUE: $native = ::core::$native::MAX;

	fn rand() -> $native {
	rand::random()
	}
	}

	impl<O: ByteOrder> ByteOrderType for $name<O> {
	type Native = $native;
	type ByteArray = [u8; $bytes];

	const ZERO: $name<O> = $name::ZERO;

	fn new(native: $native) -> $name<O> {
	$name::new(native)
	}

	fn get(self) -> $native {
	$name::get(self)
	}

	fn set(&mut self, native: $native) {
	$name::set(self, native)
	}

	fn from_bytes(bytes: [u8; $bytes]) -> $name<O> {
	$name::from(bytes)
	}

	fn into_bytes(self) -> [u8; $bytes] {
	<[u8; $bytes]>::from(self)
	}
	}

	impl_byte_order_type_unsigned!($name, $sign);
	};
	}

	impl_traits!(U16, u16, 2, unsigned);
	impl_traits!(U32, u32, 4, unsigned);
	impl_traits!(U64, u64, 8, unsigned);
	impl_traits!(U128, u128, 16, unsigned);
	impl_traits!(I16, i16, 2, signed);
	impl_traits!(I32, i32, 4, signed);
	impl_traits!(I64, i64, 8, signed);
	impl_traits!(I128, i128, 16, signed);

	macro_rules! call_for_all_types {
	($fn:ident, $byteorder:ident) => {
	$fn::<U16<$byteorder>>();
	$fn::<U32<$byteorder>>();
	$fn::<U64<$byteorder>>();
	$fn::<U128<$byteorder>>();
	$fn::<I16<$byteorder>>();
	$fn::<I32<$byteorder>>();
	$fn::<I64<$byteorder>>();
	$fn::<I128<$byteorder>>();
	};
	}

	macro_rules! call_for_unsigned_types {
	($fn:ident, $byteorder:ident) => {
	$fn::<U16<$byteorder>>();
	$fn::<U32<$byteorder>>();
	$fn::<U64<$byteorder>>();
	$fn::<U128<$byteorder>>();
	};
	}

	#[cfg(target_endian = "big")]
	type NonNativeEndian = byteorder::LittleEndian;
	#[cfg(target_endian = "little")]
	type NonNativeEndian = byteorder::BigEndian;

	#[test]
	fn test_zero() {
	fn test_zero<T: ByteOrderType>() {
	assert_eq!(T::ZERO.get(), T::Native::ZERO);
	}

	call_for_all_types!(test_zero, NativeEndian);
	call_for_all_types!(test_zero, NonNativeEndian);
	}

	#[test]
	fn test_max_value() {
	fn test_max_value<T: ByteOrderTypeUnsigned>() {
	assert_eq!(T::MAX_VALUE.get(), T::Native::MAX_VALUE);
	}

	call_for_unsigned_types!(test_max_value, NativeEndian);
	call_for_unsigned_types!(test_max_value, NonNativeEndian);
	}

	#[test]
	fn test_native_endian() {
	fn test_native_endian<T: ByteOrderType>() {
	for _ in 0..1024 {
	let native = T::Native::rand();
	let mut bytes = T::ByteArray::default();
	bytes.as_bytes_mut().copy_from_slice(native.as_bytes());
	let mut from_native = T::new(native);
	let from_bytes = T::from_bytes(bytes);
	assert_eq!(from_native, from_bytes);
	assert_eq!(from_native.get(), native);
	assert_eq!(from_bytes.get(), native);
	assert_eq!(from_native.into_bytes(), bytes);
	assert_eq!(from_bytes.into_bytes(), bytes);

	let updated = T::Native::rand();
	from_native.set(updated);
	assert_eq!(from_native.get(), updated);
	}
	}

	call_for_all_types!(test_native_endian, NativeEndian);
	}

	#[test]
	fn test_non_native_endian() {
	fn test_non_native_endian<T: ByteOrderType>() {
	for _ in 0..1024 {
	let native = T::Native::rand();
	let mut bytes = T::ByteArray::default();
	bytes.as_bytes_mut().copy_from_slice(native.as_bytes());
	bytes = bytes.invert();
	let mut from_native = T::new(native);
	let from_bytes = T::from_bytes(bytes);
	assert_eq!(from_native, from_bytes);
	assert_eq!(from_native.get(), native);
	assert_eq!(from_bytes.get(), native);
	assert_eq!(from_native.into_bytes(), bytes);
	assert_eq!(from_bytes.into_bytes(), bytes);

	let updated = T::Native::rand();
	from_native.set(updated);
	assert_eq!(from_native.get(), updated);
	}
	}

	call_for_all_types!(test_non_native_endian, NonNativeEndian);
	}
	}