File: alignof.h

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/* Determine alignment of types.
   Copyright (C) 2003-2004, 2006, 2009-2020 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
   the Free Software Foundation; either version 3, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, see <https://www.gnu.org/licenses/>.  */

#ifndef _ALIGNOF_H
#define _ALIGNOF_H

#include <stddef.h>

/* alignof_slot (TYPE)
   Determine the alignment of a structure slot (field) of a given type,
   at compile time.  Note that the result depends on the ABI.
   This is the same as alignof (TYPE) and _Alignof (TYPE), defined in
   <stdalign.h> if __alignof_is_defined is 1.
   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_slot(type) offsetof (alignof_helper<type>, __slot2)
#else
# define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
#endif

/* alignof_type (TYPE)
   Determine the good alignment of an 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__ || defined __IBM__ALIGNOF__
# define alignof_type __alignof__
#else
# define alignof_type alignof_slot
#endif

#endif /* _ALIGNOF_H */