From 3bb62e4dc4ae7e07ba8a373e804c86b96137f2ec Mon Sep 17 00:00:00 2001
From: Erin <erin@hashbang.sh>
Date: Sun, 4 Jun 2017 15:54:12 -0500
Subject: [PATCH] memory::paging::Page: impl useful functions

---
 src/arch/x86_64/memory/paging/mod.rs | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/src/arch/x86_64/memory/paging/mod.rs b/src/arch/x86_64/memory/paging/mod.rs
index 7cd63be..99c123e 100644
--- a/src/arch/x86_64/memory/paging/mod.rs
+++ b/src/arch/x86_64/memory/paging/mod.rs
@@ -40,3 +40,32 @@ impl ActivePageTable {
 pub struct Page {
     index: usize,
 }
+
+impl Page {
+    /// Retrieves the page containing a given virtual address.
+    pub fn containing_address(address: VirtualAddress) -> Page {
+        assert!(address < 0x0000_8000_0000_0000 ||
+            address >= 0xffff_8000_0000_0000,
+            "invalid address: 0x{:x}", address);
+
+        Page { index: address / PAGE_SIZE }
+    }
+
+    /// Returns the start (virtual) address of a page
+    pub fn start_address(&self) -> VirtualAddress {
+        self.index * PAGE_SIZE
+    }
+
+    fn p4_index(&self) -> usize {
+        (self.index >> 27) & 0o777
+    }
+    fn p3_index(&self) -> usize {
+        (self.index >> 18) & 0o777
+    }
+    fn p2_index(&self) -> usize {
+        (self.index >> 9) & 0o777
+    }
+    fn p1_index(&self) -> usize {
+        (self.index >> 0) & 0o777
+    }
+}