[PATCH] rust: kernel: add support for bits/genmask macros

[Daniel Almeida <daniel.almeida@collabora.com>]

These macros were converted from their C equivalent.
---

Hey all, I did not see any patch for this floating in the mailing list.

Please let me know your thoughts. This one should be rather trivial.


 rust/kernel/bits.rs | 32 ++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs  |  1 +
 2 files changed, 33 insertions(+)
 create mode 100644 rust/kernel/bits.rs

diff --git a/rust/kernel/bits.rs b/rust/kernel/bits.rs
new file mode 100644
index 000000000000..8ac142392086
--- /dev/null
+++ b/rust/kernel/bits.rs
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Bit manipulation macros.
+//!
+//! C header: [`include/linux/bits.h`](srctree/include/linux/bits.h)
+
+/// Produces a literal where bit `n` is set.
+///
+/// Equivalent to the kernel's BIT macro.
+///
+#[macro_export]
+macro_rules! bit {
+    ($n:expr) => {
+        (1 << $n)
+    };
+}
+
+/// Create a contiguous bitmask starting at bit position `l` and ending at
+/// position `h`, where h <= l.
+///
+/// For example genmask(39, 21) gives us the 64bit vector
+/// 0x000000ffffe00000.
+///
+#[macro_export]
+macro_rules! genmask {
+    ($h:expr, $l:expr) => {{
+        const _: () = {
+            assert!($h >= $l);
+        };
+        ((!0u64 - (1u64 << $l) + 1) & (!0u64 >> (64 - 1 - $h)))
+    }};
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 274bdc1b0a82..3aaa1c410d2c 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -27,6 +27,7 @@
 extern crate self as kernel;
 
 pub mod alloc;
+pub mod bits;
 #[cfg(CONFIG_BLOCK)]
 pub mod block;
 mod build_assert;
-- 
2.45.2