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# ===========================================================================
# http://autoconf-archive.cryp.to/ax_check_aligned_access_required.html
# ===========================================================================
#
# SYNOPSIS
#
# AC_CHECK_ALIGNED_ACCESS_REQUIRED
#
# DESCRIPTION
#
# While the x86 CPUs allow access to memory objects to be unaligned it
# happens that most of the modern designs require objects to be aligned -
# or they will fail with a buserror. That mode is quite known by
# big-endian machines (sparc, etc) however the alpha cpu is little-
# endian.
#
# The following function will test for aligned access to be required and
# set a config.h define HAVE_ALIGNED_ACCESS_REQUIRED (name derived by
# standard usage). Structures loaded from a file (or mmapped to memory)
# should be accessed per-byte in that case to avoid segfault type errors.
#
# LICENSE
#
# Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
#
# This program is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 2 of the License, 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 General
# Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program. If not, see <http://www.gnu.org/licenses/>.
#
# As a special exception, the respective Autoconf Macro's copyright owner
# gives unlimited permission to copy, distribute and modify the configure
# scripts that are the output of Autoconf when processing the Macro. You
# need not follow the terms of the GNU General Public License when using
# or distributing such scripts, even though portions of the text of the
# Macro appear in them. The GNU General Public License (GPL) does govern
# all other use of the material that constitutes the Autoconf Macro.
#
# This special exception to the GPL applies to versions of the Autoconf
# Macro released by the Autoconf Archive. When you make and distribute a
# modified version of the Autoconf Macro, you may extend this special
# exception to the GPL to apply to your modified version as well.
AC_DEFUN([AX_CHECK_ALIGNED_ACCESS_REQUIRED],
[AC_CACHE_CHECK([if pointers to integers require aligned access],
[ax_cv_have_aligned_access_required],
[AC_TRY_RUN([
#include <stdio.h>
#include <stdlib.h>
int main()
{
char* string = malloc(40);
int i;
for (i=0; i < 40; i++) string[[i]] = i;
{
void* s = string;
int* p = s+1;
int* q = s+2;
if (*p == *q) { return 1; }
}
return 0;
}
],
[ax_cv_have_aligned_access_required=yes],
[ax_cv_have_aligned_access_required=no],
[ax_cv_have_aligned_access_required=no])
])
if test "$ax_cv_have_aligned_access_required" = yes ; then
AC_DEFINE([HAVE_ALIGNED_ACCESS_REQUIRED], [1],
[Define if pointers to integers require aligned access])
fi
])
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