lib/alignof.h

   1 /* Determine alignment of types.
   2    Copyright (C) 2003-2004, 2006, 2009-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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, see <https://www.gnu.org/licenses/>.  */
  16
  17 #ifndef _ALIGNOF_H
  18 #define _ALIGNOF_H
  19
  20 /* This file uses alignof.  */
  21 #if !_GL_CONFIG_H_INCLUDED
  22  #error "Please include config.h first."
  23 #endif
  24
  25 #include <stddef.h>
  26
  27 /* alignof_slot (TYPE)
  28    Determine the alignment of a structure slot (field) of a given type,
  29    at compile time.  Note that the result depends on the ABI.
  30    This is the same as alignof (TYPE).
  31    Note: The result cannot be used as a value for an 'enum' constant,
  32    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
  33 #if defined __cplusplus
  34   template <class type> struct alignof_helper { char __slot1; type __slot2; };
  35 # define alignof_slot(type) offsetof (alignof_helper<type>, __slot2)
  36 #else
  37 # define alignof_slot(type) alignof (type)
  38 #endif
  39
  40 /* alignof_type (TYPE)
  41    Determine the good alignment of an object of the given type at compile time.
  42    Note that this is not necessarily the same as alignof_slot(type).
  43    For example, with GNU C on x86 platforms and with clang on Linux/x86:
  44    alignof_type(long long) = 8, but alignof_slot(long long) = 4.
  45    And alignof_type(double) = 8, but
  46    - when -malign-double is not specified:  alignof_slot(double) = 4,
  47    - when -malign-double is specified:      alignof_slot(double) = 8.
  48    Note: The result cannot be used as a value for an 'enum' constant,
  49    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
  50 #if defined __GNUC__ || defined __clang__ || defined __IBM__ALIGNOF__
  51 # define alignof_type __alignof__
  52 #else
  53 # define alignof_type alignof_slot
  54 #endif
  55
  56 #endif /* _ALIGNOF_H */