lib/alignof.h

   1 /* Determine alignment of types.
   2    Copyright (C) 2003-2004, 2006, 2009-2010 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program; if not, write to the Free Software Foundation,
  16    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  17
  18 #ifndef _ALIGNOF_H
  19 #define _ALIGNOF_H
  20
  21 #include <stddef.h>
  22
  23 /* Determine the alignment of a structure slot (field) of a given type,
  24    at compile time.  Note that the result depends on the ABI.
  25    Note: The result cannot be used as a value for an 'enum' constant,
  26    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
  27 #if defined __cplusplus
  28   template <class type> struct alignof_helper { char __slot1; type __slot2; };
  29 # define alignof_slot(type) offsetof (alignof_helper<type>, __slot2)
  30 #else
  31 # define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
  32 #endif
  33
  34 /* Determine the good alignment of a object of the given type at compile time.
  35    Note that this is not necessarily the same as alignof_slot(type).
  36    For example, with GNU C on x86 platforms: alignof_type(double) = 8, but
  37    - when -malign-double is not specified:  alignof_slot(double) = 4,
  38    - when -malign-double is specified:      alignof_slot(double) = 8.
  39    Note: The result cannot be used as a value for an 'enum' constant,
  40    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
  41 #if defined __GNUC__
  42 # define alignof_type __alignof__
  43 #else
  44 # define alignof_type alignof_slot
  45 #endif
  46
  47 /* alignof is an alias for alignof_slot semantics, since that's what most
  48    callers need.
  49    Note: The result cannot be used as a value for an 'enum' constant,
  50    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
  51 #define alignof alignof_slot
  52
  53 #endif /* _ALIGNOF_H */