1 /* Determine alignment of types. 2 Copyright (C) 2003-2004, 2006, 2009-2021 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 #include <stddef.h> 21 22 /* alignof_slot (TYPE) 23 Determine the alignment of a structure slot (field) of a given type, 24 at compile time. Note that the result depends on the ABI. 25 This is the same as alignof (TYPE) and _Alignof (TYPE), defined in 26 <stdalign.h> if __alignof_is_defined is 1. 27 Note: The result cannot be used as a value for an 'enum' constant, 28 due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */ 29 #if defined __cplusplus 30 template <class type> struct alignof_helper { char __slot1; type __slot2; }; 31 # define alignof_slot(type) offsetof (alignof_helper<type>, __slot2) 32 #else 33 # define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) 34 #endif 35 36 /* alignof_type (TYPE) 37 Determine the good alignment of an object of the given type at compile time. 38 Note that this is not necessarily the same as alignof_slot(type). 39 For example, with GNU C on x86 platforms and with clang on Linux/x86: 40 alignof_type(long long) = 8, but alignof_slot(long long) = 4. 41 And alignof_type(double) = 8, but 42 - when -malign-double is not specified: alignof_slot(double) = 4, 43 - when -malign-double is specified: alignof_slot(double) = 8. 44 Note: The result cannot be used as a value for an 'enum' constant, 45 due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */ 46 #if defined __GNUC__ || defined __clang__ || defined __IBM__ALIGNOF__ 47 # define alignof_type __alignof__ 48 #else 49 # define alignof_type alignof_slot 50 #endif 51 52 #endif /* _ALIGNOF_H */