constify align_down, is_aligned & into

We can't constify the public methods because const traits are not yet
stable, but we can introduce private const methods that don't use
traits. We'll use these internally in other const methods.

Author: Freax13

src/addr.rs

@@ -177,7 +177,15 @@ impl VirtAddr {
     where
         U: Into<u64>,
     {
-        VirtAddr::new_truncate(align_down(self.0, align.into()))
+        self.align_down_u64(align.into())
+    }
+
+    /// Aligns the virtual address downwards to the given alignment.
+    ///
+    /// See the `align_down` function for more information.
+    #[inline]
+    pub(crate) const fn align_down_u64(self, align: u64) -> Self {
+        VirtAddr::new_truncate(align_down(self.0, align))
     }
 
     /// Checks whether the virtual address has the demanded alignment.
@@ -186,7 +194,13 @@ impl VirtAddr {
     where
         U: Into<u64>,
     {
-        self.align_down(align) == self
+        self.is_aligned_u64(align.into())
+    }
+
+    /// Checks whether the virtual address has the demanded alignment.
+    #[inline]
+    pub(crate) const fn is_aligned_u64(self, align: u64) -> bool {
+        self.align_down_u64(align).as_u64() == self.as_u64()
     }
 
     /// Returns the 12-bit page offset of this virtual address.

src/structures/paging/page_table.rs

@@ -306,6 +306,10 @@ impl PageTableIndex {
     pub const fn new_truncate(index: u16) -> Self {
         Self(index % ENTRY_COUNT as u16)
     }
+
+    pub(crate) const fn into_u64(self) -> u64 {
+        self.0 as u64
+    }
 }
 
 impl From<PageTableIndex> for u16 {
@@ -325,7 +329,7 @@ impl From<PageTableIndex> for u32 {
 impl From<PageTableIndex> for u64 {
     #[inline]
     fn from(index: PageTableIndex) -> Self {
-        u64::from(index.0)
+        index.into_u64()
     }
 }