guile/lib/alignof.h

/* Determine alignment of types.
   Copyright (C) 2003-2004, 2006, 2009-2010 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as published by
   the Free Software Foundation; either version 2, 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 Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

#ifndef _ALIGNOF_H
#define _ALIGNOF_H

#include <stddef.h>

/* 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_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 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 */