Refactor to integer with access methods

Signed-off-by: Marcus Weiner <[email protected]>

riscv64/src/mem.rs

@@ -16,8 +16,12 @@ bitflags! {
   }
 }
 
-#[derive(Clone, Copy, Debug)]
-struct SizedInteger<const N: usize>(u64);
+/// Used as an index for PPN and VPN
+pub enum PN {
+    _0,
+    _1,
+    _2,
+}
 
 #[derive(Debug)]
 pub struct NumberTooLarge;
@@ -47,14 +51,27 @@ pub struct PageTableEntry {
     flags: PageTableFlags,
 }
 
+#[derive(Debug)]
+pub struct PageTableEntry(u64);
+
 impl PageTableEntry {
-    pub fn serialize(&self) -> u64 {
-        let mut out = 0u64;
-        out.set_bits(0..=7, self.flags.bits() as _);
-        out.set_bits(10..=18, self.ppn0.into());
-        out.set_bits(19..=27, self.ppn1.into());
-        out.set_bits(28..=53, self.ppn2.into());
-        out
+    pub unsafe fn write_to(&self, addr: u64) {
+        unsafe { write_volatile(addr as *mut u64, self.0) }
+    }
+
+    pub fn ppn(&self, i: PN) -> u64 {
+        use PN::*;
+        match i {
+            _0 => self.0.get_bits(10..=18),
+            _1 => self.0.get_bits(19..=27),
+            _2 => self.0.get_bits(28..=53),
+        }
+    }
+
+    pub fn flags(&self) -> PageTableFlags {
+        let bits = self.0.get_bits(0..=7) as u8;
+        // safe to unwrap since all bits of a u8 are defined flags
+        PageTableFlags::from_bits(bits).unwrap()
     }
 
     pub unsafe fn write_to(&self, addr: u64) {
@@ -64,13 +81,13 @@ impl PageTableEntry {
 
 impl From<u64> for PageTableEntry {
     fn from(value: u64) -> Self {
-        let flags = PageTableFlags::from_bits(value.get_bits(0..=7) as _).unwrap();
-        Self {
-            ppn2: value.get_bits(28..=53).try_into().unwrap(),
-            ppn1: value.get_bits(19..=27).try_into().unwrap(),
-            ppn0: value.get_bits(10..=18).try_into().unwrap(),
-            flags,
-        }
+        Self(value)
+    }
+}
+
+impl From<PageTableEntry> for u64 {
+    fn from(value: PageTableEntry) -> Self {
+        value.0
     }
 }