fix: preserve merged block when frame deallocation reaches the top order

src/frame.rs

@@ -153,18 +153,18 @@ impl<const ORDER: usize> FrameAllocator<ORDER> {
         // Merge free buddy lists
         let mut current_ptr = start_frame;
         let mut current_class = class;
-        while current_class < self.free_list.len() {
+        while current_class < self.free_list.len() - 1 {
             let buddy = current_ptr ^ (1 << current_class);
             if self.free_list[current_class].remove(&buddy) {
                 // Free buddy found
                 current_ptr = min(current_ptr, buddy);
                 current_class += 1;
             } else {
-                self.free_list[current_class].insert(current_ptr);
                 break;
             }
         }
 
+        self.free_list[current_class].insert(current_ptr);
         self.allocated -= size;
     }
 }

src/test.rs

@@ -211,6 +211,20 @@ fn test_frame_allocator_aligned() {
     );
 }
 
+#[test]
+fn test_frame_allocator_merge_final_order() {
+    let mut frame = FrameAllocator::<2>::new();
+    frame.add_frame(0, 4);
+
+    let first = frame.alloc(2).unwrap();
+    let second = frame.alloc(2).unwrap();
+
+    frame.dealloc(first, 2);
+    frame.dealloc(second, 2);
+
+    assert_eq!(frame.alloc(2), Some(0));
+}
+
 #[test]
 fn test_heap_merge_final_order() {
     const NUM_ORDERS: usize = 5;