1  /* Determine alignment of types.
       2     Copyright (C) 2003-2004, 2006, 2009-2023 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 */