X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=lib%2Falignof.h;h=24f4bc9b4c5004e1584af0d5fb293b201887b5bd;hb=3d50b6043ac61690f0b163a1618cfd5516238c81;hp=3752ef39424ee1f9fc808367c5b82102f6d6d4be;hpb=4a5848d1059d31db026bb893fb28af28b4a97985;p=gnulib.git

diff --git a/lib/alignof.h b/lib/alignof.h
index 3752ef394..24f4bc9b4 100644
--- a/lib/alignof.h
+++ b/lib/alignof.h
@@ -1,5 +1,5 @@
 /* Determine alignment of types.
-   Copyright (C) 2003-2004, 2006, 2009 Free Software Foundation, Inc.
+   Copyright (C) 2003-2004, 2006, 2009-2011 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -20,14 +20,34 @@
 
 #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.
+   Note: The result cannot be used as a value for an 'enum' constant,
+   due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
+#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_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.
+   Note: The result cannot be used as a value for an 'enum' constant,
+   due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
+#if defined __GNUC__
+# define alignof_type __alignof__
 #else
-# define alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
+# 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,
+   due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
+#define alignof alignof_slot
+
 #endif /* _ALIGNOF_H */