Make sure to align pointers in alloc_layout_slow

src/lib.rs

@@ -636,6 +636,10 @@ impl Bump {
             let current_layout = current_footer.as_ref().layout;
             let new_footer =
                 Bump::new_chunk(Some((current_layout.size(), layout)), Some(current_footer));
+            debug_assert_eq!(
+                new_footer.as_ref().data.as_ptr() as usize % layout.align(),
+                0
+            );
 
             // Set the new chunk as our new current chunk.
             self.current_chunk_footer.set(new_footer);
@@ -646,6 +650,8 @@ impl Bump {
             // this can't overflow because we successfully allocated a chunk of
             // at least the requested size.
             let ptr = new_footer.ptr.get().as_ptr() as usize - size;
+            // Round the pointer down to the requested alignment.
+            let ptr = ptr & !(layout.align() - 1);
             debug_assert!(
                 ptr <= new_footer as *const _ as usize,
                 "{:#x} <= {:#x}",

tests/tests.rs

@@ -180,3 +180,15 @@ fn test_reset() {
     );
     assert_eq!(b.iter_allocated_chunks().count(), 1);
 }
+
+#[test]
+fn test_alignment() {
+    let b = Bump::new();
+
+    let layout = std::alloc::Layout::from_size_align(64, 64).unwrap();
+
+    for _ in 0..1024 {
+        let ptr = b.alloc_layout(layout).as_ptr();
+        assert_eq!(ptr as *const u8 as usize % 64, 0);
+    }
+}