diff --git a/port/src/bitmapalloc.rs b/port/src/bitmapalloc.rs
index 110a4f7..cc917e7 100644
--- a/port/src/bitmapalloc.rs
+++ b/port/src/bitmapalloc.rs
@@ -13,6 +13,7 @@ impl<const SIZE_BYTES: usize> Bitmap<SIZE_BYTES> {
         Self { bytes: [init_value; SIZE_BYTES] }
     }
 
+    /// Is bit `i` within the bitmap set?
     pub fn is_set(&self, i: usize) -> bool {
         let byteidx = i / 8;
         let bitidx = i % 8;
@@ -20,6 +21,7 @@ impl<const SIZE_BYTES: usize> Bitmap<SIZE_BYTES> {
         byte & (1 << bitidx) > 0
     }
 
+    /// Set bit `i` within the bitmap
     pub fn set(&mut self, i: usize, b: bool) {
         let byteidx = i / 8;
         let bitidx = i % 8;
@@ -149,17 +151,13 @@ impl<const NUM_BITMAPS: usize, const BITMAP_SIZE_BYTES: usize>
             return Err(BitmapPageAllocError::OutOfBounds);
         }
 
-        let bytes_per_bitmap = self.bytes_per_bitmap();
-        let bitmap_idx = pa.addr() as usize / bytes_per_bitmap;
-
-        let offset_into_bitmap = pa.addr() as usize % bytes_per_bitmap;
-        let bitmap_byte_idx = offset_into_bitmap / self.alloc_page_size;
+        let (bitmap_idx, bit_idx) = self.physaddr_as_indices(pa);
 
         let bitmap = &mut self.bitmaps[bitmap_idx];
-        if !bitmap.is_set(bitmap_byte_idx) {
+        if !bitmap.is_set(bit_idx) {
             return Err(BitmapPageAllocError::NotAllocated);
         }
-        bitmap.set(bitmap_byte_idx, false);
+        bitmap.set(bit_idx, false);
 
         Ok(())
     }
@@ -176,6 +174,20 @@ impl<const NUM_BITMAPS: usize, const BITMAP_SIZE_BYTES: usize>
         (total - free_bytes, total)
     }
 
+    /// For the given physaddr, returns a tuple of
+    /// (the bitmap containing pa, and the index of the bit within that bitmap).
+    fn physaddr_as_indices(&self, pa: PhysAddr) -> (usize, usize) {
+        // Get the index of the bitmap containing the pa
+        let bytes_per_bitmap = self.bytes_per_bitmap();
+        let bitmap_idx = pa.addr() as usize / bytes_per_bitmap;
+
+        // Get the bit within the bitmap representing the pa
+        let pa_offset_into_bitmap = pa.addr() as usize % bytes_per_bitmap;
+        let bit_idx = pa_offset_into_bitmap / self.alloc_page_size;
+
+        (bitmap_idx, bit_idx)
+    }
+
     fn mark_range(
         &mut self,
         range: &PhysRange,
@@ -186,18 +198,14 @@ impl<const NUM_BITMAPS: usize, const BITMAP_SIZE_BYTES: usize>
             return Err(BitmapPageAllocError::OutOfBounds);
         }
 
-        let bytes_per_bitmap = self.bytes_per_bitmap();
         for pa in range.step_by_rounded(self.alloc_page_size) {
-            let bitmap_idx = pa.addr() as usize / bytes_per_bitmap;
+            let (bitmap_idx, bit_idx) = self.physaddr_as_indices(pa);
             if bitmap_idx >= self.bitmaps.len() {
                 return Err(BitmapPageAllocError::OutOfBounds);
             }
 
-            let offset_into_bitmap = pa.addr() as usize % bytes_per_bitmap;
-            let bitmap_byte_idx = offset_into_bitmap / self.alloc_page_size;
-
             let bitmap = &mut self.bitmaps[bitmap_idx];
-            bitmap.set(bitmap_byte_idx, mark_allocated);
+            bitmap.set(bit_idx, mark_allocated);
         }
         Ok(())
     }