Add a BITS constant in preparation for #76904

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes will be documented in this file.
 
 This document is written according to the [Keep a Changelog][kac] style.
 
+## 1.2
+
+Add `BITS` in preparation for [`rust-lang/rust#76904`].
+
 ## 1.1
 
 Add `leading_ones` and `trailing_ones`, as these methods were introduced in Rust
@@ -23,3 +27,4 @@ The width relation traits allow users to constrain the widths of numbers they
 require.
 
 [kac]: //keepachangelog.com/en/1.0.0/
+[`rust-lang/rust#76904`]: https://github.com/rust-lang/rust/issues/76904

src/lib.rs

@@ -137,8 +137,12 @@ pub trait IsNumber: Sized
 	+ RemAssign<Self>
 	+ for<'a> RemAssign<&'a Self>
 {
+	/// The `[u8; N]` byte array that stores values of `Self`.
 	type Bytes;
 
+	/// The size of this numeric type in bits.
+	const BITS: u32;
+
 	/// Return the memory representation of this number as a byte array in
 	/// big-endian (network) byte order.
 	fn to_be_bytes(self) -> Self::Bytes;
@@ -1294,6 +1298,10 @@ macro_rules! impl_for {
 		impl IsNumber for $t {
 			type Bytes = [u8; core::mem::size_of::<Self>()];
 
+			//  This can be replaced with the `::BITS` inherent once it
+			//  stabilizes in the standard library.
+			const BITS: u32 = core::mem::size_of::<Self>() as u32 * 8;
+
 			func!(to_be_bytes(self) -> Self::Bytes);
 			func!(to_le_bytes(self) -> Self::Bytes);
 			func!(to_ne_bytes(self) -> Self::Bytes);