fix: handle zero start correctly when splitting frame ranges

src/frame.rs

@@ -55,16 +55,17 @@ impl<const ORDER: usize> FrameAllocator<ORDER> {
 
         let mut total = 0;
         let mut current_start = start;
+        let max_block_size = 1 << (ORDER - 1);
 
         while current_start < end {
             let lowbit = if current_start > 0 {
                 current_start & (!current_start + 1)
             } else {
-                32
+                max_block_size
             };
             let size = min(
                 min(lowbit, prev_power_of_two(end - current_start)),
-                1 << (ORDER - 1),
+                max_block_size,
             );
             total += size;
 

src/test.rs

@@ -139,6 +139,15 @@ fn test_frame_allocator_add() {
     assert!(frame.alloc(2).is_none());
 }
 
+#[test]
+fn test_frame_allocator_add_from_zero_keeps_large_block() {
+    let mut frame = FrameAllocator::<7>::new();
+
+    frame.add_frame(0, 64);
+
+    assert_eq!(frame.alloc(64), Some(0));
+}
+
 #[test]
 fn test_frame_allocator_allocate_large() {
     let mut frame = FrameAllocator::<32>::new();
@@ -152,16 +161,16 @@ fn test_frame_allocator_add_large_size_split() {
     frame.insert(0..10_000_000_000);
 
     assert_eq!(frame.alloc(0x8000_0001), None);
+    assert_eq!(frame.alloc(0x8000_0000), Some(0));
     assert_eq!(frame.alloc(0x8000_0000), Some(0x8000_0000));
-    assert_eq!(frame.alloc(0x8000_0000), Some(0x1_0000_0000));
 }
 
 #[test]
 fn test_frame_allocator_add_large_size() {
     let mut frame = FrameAllocator::<33>::new();
 
     frame.insert(0..10_000_000_000);
-    assert_eq!(frame.alloc(0x8000_0001), Some(0x1_0000_0000));
+    assert_eq!(frame.alloc(0x8000_0001), Some(0));
 }
 
 #[test]