--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2009-05-31  Simon Josefsson  <simon@josefsson.org>
+            Bruno Haible  <bruno@clisp.org>
+
+	Fix test-alignof failure.
+	* lib/alignof.h (alignof_slot): New macro.
+	(alignof_type): New macro, with the same semantics as the previous
+	'alignof'.
+	(alignof): Alias to alignof_slot.
+	* tests/test-alignof.c (CHECK): Check alignof_slot, not alignof. Also
+	check that the results are usable as constant expressions.
+
 2009-05-31  Bruno Haible  <bruno@clisp.org>
 
 	* tests/zerosize-ptr.h (zerosize_ptr): Specify more details.

--- a/lib/alignof.h
+++ b/lib/alignof.h
@@ -20,14 +20,29 @@
 
 #include <stddef.h>
 
-/* Determine the alignment of a type at compile time.  */
-#if defined __GNUC__
-# define alignof __alignof__
-#elif defined __cplusplus
+/* Determine the alignment of a structure slot (field) of a given type,
+   at compile time.  Note that the result depends on the ABI.  */
+#if defined __cplusplus
   template <class type> struct alignof_helper { char __slot1; type __slot2; };
-# define alignof(type) offsetof (alignof_helper<type>, __slot2)
+# define alignof_slot(type) offsetof (alignof_helper<type>, __slot2)
 #else
-# define alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
+# 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__
+#else
+# define alignof_type alignof_slot
+#endif
+
+/* alignof is an alias for alignof_slot semantics, since that's what most
+   callers need.
+   Note: The result cannot be used as a value for an 'enum' constant,  */
+#define alignof alignof_slot
+
 #endif /* _ALIGNOF_H */

--- a/tests/test-alignof.c
+++ b/tests/test-alignof.c
@@ -31,7 +31,9 @@
 
 #define CHECK(type) \
   typedef struct { char slot1; type slot2; } type##_helper; \
-  verify (alignof (type) == offsetof (type##_helper, slot2));
+  verify (alignof_slot (type) == offsetof (type##_helper, slot2)); \
+  const int type##_slot_alignment = alignof_slot (type); \
+  const int type##_type_alignment = alignof_type (type);
 
 CHECK (char)
 CHECK (short)