Finish basics of new paging module

src/memory/paging/translate.rs

@@ -0,0 +1,42 @@
+use super::{VirtualAddress, PhysicalAddress, Page, PAGE_SIZE, ENTRY_COUNT};
+use super::table::P4;
+use super::entry::{PRESENT, HUGE_PAGE};
+use memory::Frame;
+
+pub fn translate(virtual_address: VirtualAddress) -> Option<PhysicalAddress> {
+    let page = Page::containing_address(virtual_address);
+    let offset = virtual_address % PAGE_SIZE;
+
+    let p4 = unsafe { &*P4 };
+
+    let huge_page = || {
+        p4.next_table(page.p4_index())
+          .and_then(|p3| {
+              // 1GiB page?
+              if p3[page.p3_index()].flags().contains(HUGE_PAGE | PRESENT) {
+                  let start_frame_number = p3[page.p3_index()].pointed_frame().number;
+                  // address must be 1GiB aligned
+                  assert!(start_frame_number % (ENTRY_COUNT * ENTRY_COUNT) == 0);
+                  return Some(start_frame_number + page.p2_index() * ENTRY_COUNT + page.p1_index());
+              }
+              if let Some(p2) = p3.next_table(page.p3_index()) {
+                  // 2MiB page?
+                  if p2[page.p2_index()].flags().contains(HUGE_PAGE | PRESENT) {
+                      let start_frame_number = p2[page.p2_index()].pointed_frame().number;
+                      // address must be 2MiB aligned
+                      assert!(start_frame_number % ENTRY_COUNT == 0);
+                      return Some(start_frame_number + page.p1_index());
+                  }
+              }
+              None
+          })
+          .map(|start_frame_number| Frame { number: start_frame_number })
+    };
+
+    p4.next_table(page.p4_index())
+      .and_then(|p3| p3.next_table(page.p3_index()))
+      .and_then(|p2| p2.next_table(page.p2_index()))
+      .map(|p1| p1[page.p1_index()].pointed_frame())
+      .or_else(huge_page)
+      .map(|frame| frame.number * PAGE_SIZE + offset)
+}