rust: add num module and Integer trait

Introduce the `num` module, which will provide numerical extensions and
utilities for the kernel.

For now, introduce the `Integer` trait, which is implemented for all
primitive integer types to provides their core properties to generic
code.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20251108-bounded_ints-v4-1-c9342ac7ebd1@nvidia.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/kernel/lib.rs

@@ -109,6 +109,7 @@
 pub mod mm;
 #[cfg(CONFIG_NET)]
 pub mod net;
+pub mod num;
 pub mod of;
 #[cfg(CONFIG_PM_OPP)]
 pub mod opp;

rust/kernel/num.rs

@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Additional numerical features for the kernel.
+
+use core::ops;
+
+/// Designates unsigned primitive types.
+pub enum Unsigned {}
+
+/// Designates signed primitive types.
+pub enum Signed {}
+
+/// Describes core properties of integer types.
+pub trait Integer:
+    Sized
+    + Copy
+    + Clone
+    + PartialEq
+    + Eq
+    + PartialOrd
+    + Ord
+    + ops::Add<Output = Self>
+    + ops::AddAssign
+    + ops::Sub<Output = Self>
+    + ops::SubAssign
+    + ops::Mul<Output = Self>
+    + ops::MulAssign
+    + ops::Div<Output = Self>
+    + ops::DivAssign
+    + ops::Rem<Output = Self>
+    + ops::RemAssign
+    + ops::BitAnd<Output = Self>
+    + ops::BitAndAssign
+    + ops::BitOr<Output = Self>
+    + ops::BitOrAssign
+    + ops::BitXor<Output = Self>
+    + ops::BitXorAssign
+    + ops::Shl<u32, Output = Self>
+    + ops::ShlAssign<u32>
+    + ops::Shr<u32, Output = Self>
+    + ops::ShrAssign<u32>
+    + ops::Not
+{
+    /// Whether this type is [`Signed`] or [`Unsigned`].
+    type Signedness;
+
+    /// Number of bits used for value representation.
+    const BITS: u32;
+}
+
+macro_rules! impl_integer {
+    ($($type:ty: $signedness:ty), *) => {
+        $(
+        impl Integer for $type {
+            type Signedness = $signedness;
+
+            const BITS: u32 = <$type>::BITS;
+        }
+        )*
+    };
+}
+
+impl_integer!(
+    u8: Unsigned,
+    u16: Unsigned,
+    u32: Unsigned,
+    u64: Unsigned,
+    u128: Unsigned,
+    usize: Unsigned,
+    i8: Signed,
+    i16: Signed,
+    i32: Signed,
+    i64: Signed,
+    i128: Signed,
+    isize: Signed
+);