lib/alignof.h

   1 /* Determine alignment of types.
   2    Copyright (C) 2003-2004, 2006, 2009-2011 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 /* alignof_slot (TYPE)
  24    Determine the alignment of a structure slot (field) of a given type,
  25    at compile time.  Note that the result depends on the ABI.
  26    This is the same as alignof (TYPE) and _Alignof (TYPE), defined in
  27    <stdalign.h> if __alignof_is_defined is 1.
  28    Note: The result cannot be used as a value for an 'enum' constant,
  29    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
  30 #if defined __cplusplus
  31   template <class type> struct alignof_helper { char __slot1; type __slot2; };
  32 # define alignof_slot(type) offsetof (alignof_helper<type>, __slot2)
  33 #else
  34 # define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
  35 #endif
  36
  37 /* alignof_type (TYPE)
  38    Determine the good alignment of an object of the given type at compile time.
  39    Note that this is not necessarily the same as alignof_slot(type).
  40    For example, with GNU C on x86 platforms: alignof_type(double) = 8, but
  41    - when -malign-double is not specified:  alignof_slot(double) = 4,
  42    - when -malign-double is specified:      alignof_slot(double) = 8.
  43    Note: The result cannot be used as a value for an 'enum' constant,
  44    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
  45 #if defined __GNUC__
  46 # define alignof_type __alignof__
  47 #else
  48 # define alignof_type alignof_slot
  49 #endif
  50
  51 #endif /* _ALIGNOF_H */