fix ArenaPtr payload offset logic

the old logic would be incorrect if the payload has higher alignment than the ArenaHeader i.e. when there is padding between the ArenaHeader and the Payload

diff --git a/src/arena.rs b/src/arena.rs
index 1b5cd3e5a808b37c47b754dd62c3893165b453f2..ffb92fb74c3b3b85713d9fb6ac5090f6f8f6ce14 100644 (file)
--- a/src/arena.rs
+++ b/src/arena.rs
@@ -283,7 +283,10 @@ pub trait ArenaAllocated {
         Self::Payload: Sized,
     {
         TypedArenaPtr(NonNull::new_unchecked(
-            ptr.payload_offset().cast_mut().cast::<Self::Payload>(),
+            ptr.get_ptr()
+                .byte_add(Self::header_offset_from_payload())
+                .cast_mut()
+                .cast::<Self::Payload>(),
         ))
     }
 

diff --git a/src/types.rs b/src/types.rs
index 994a6a27dcfc4bebec03967f1cff9225663c1ae8..bcf67a4a01d2b250f42b6585828ad7143abc35a6 100644 (file)
--- a/src/types.rs
+++ b/src/types.rs
@@ -754,11 +754,6 @@ impl UntypedArenaPtr {
         }
     }
 
-    #[inline]
-    pub fn payload_offset(self) -> *const u8 {
-        unsafe { self.get_ptr().byte_add(size_of::<ArenaHeader>()).cast() }
-    }
-
     /// # Safety
     /// - this UntypedArenaPtr actual pointee type is T
     /// - the pointer must be non-null