[PATCH v6 19/34] rust: ptr: add const_align_up()

[John Hubbard]

Add const_align_up() to kernel::ptr as the const-compatible equivalent
of Alignable::align_up().

Suggested-by: Danilo Krummrich <dakr@xxxxxxxxxx>
Suggested-by: Gary Guo <gary@xxxxxxxxxxx>
Suggested-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
---
 rust/kernel/ptr.rs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/rust/kernel/ptr.rs b/rust/kernel/ptr.rs
index 5b6a382637fe..1e15aac4faca 100644
--- a/rust/kernel/ptr.rs
+++ b/rust/kernel/ptr.rs
@@ -225,3 +225,27 @@ fn align_up(self, alignment: Alignment) -> Option<Self> {
 }
 
 impl_alignable_uint!(u8, u16, u32, u64, usize);
+
+/// Aligns `value` up to `align`.
+///
+/// This is the const-compatible equivalent of [`Alignable::align_up`].
+///
+/// Returns [`None`] on overflow.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::ptr::{const_align_up, Alignment};
+/// use kernel::sizes::SZ_4K;
+///
+/// assert_eq!(const_align_up(0x4f, Alignment::new::<16>()), Some(0x50));
+/// assert_eq!(const_align_up(0x40, Alignment::new::<16>()), Some(0x40));
+/// assert_eq!(const_align_up(1, Alignment::new::<SZ_4K>()), Some(SZ_4K));
+/// ```
+#[inline(always)]
+pub const fn const_align_up(value: usize, align: Alignment) -> Option<usize> {
+    match value.checked_add(align.as_usize() - 1) {
+        Some(v) => Some(v & align.mask()),
+        None => None,
+    }
+}
-- 
2.53.0