config/bitfields.m4

   1 dnl Copyright (C) 2015 Free Software Foundation, Inc.
   2 dnl This file is free software, distributed under the terms of the GNU
   3 dnl General Public License.  As a special exception to the GNU General
   4 dnl Public License, this file may be distributed as part of a program
   5 dnl that contains a configuration script generated by Autoconf, under
   6 dnl the same distribution terms as the rest of that program.
   7
   8 # Define HAVE_BITFIELD_TYPE_MATTERS if the type of bitfields effects their
   9 # alignment.
  10
  11 AC_DEFUN([gt_BITFIELD_TYPE_MATTERS],
  12 [
  13   AC_CACHE_CHECK([if the type of bitfields matters], gt_cv_bitfield_type_matters,
  14   [
  15     AC_TRY_COMPILE(
  16       [struct foo1 { char x; char y:1; char z; };
  17 struct foo2 { char x; long long int y:1; char z; };
  18 int foo1test[ sizeof (struct foo1) < sizeof (struct foo2) ? 1 : -1 ]; ],
  19       [], gt_cv_bitfield_type_matters=yes, gt_cv_bitfield_type_matters=no)
  20   ])
  21   if test $gt_cv_bitfield_type_matters = yes; then
  22     AC_DEFINE(HAVE_BITFIELD_TYPE_MATTERS, 1,
  23       [Define if the type of bitfields effects alignment.])
  24   fi
  25 ])