+# define alignof_slot(type) offsetof (alignof_helper<type>, __slot2)
+#else
+# define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
+#endif
+
+/* Determine the good alignment of a object of the given type at compile time.
+ Note that this is not necessarily the same as alignof_slot(type).
+ For example, with GNU C on x86 platforms: alignof_type(double) = 8, but
+ - when -malign-double is not specified: alignof_slot(double) = 4,
+ - when -malign-double is specified: alignof_slot(double) = 8. */
+#if defined __GNUC__
+# define alignof_type __alignof__