m4/ax_check_aligned_access_required.m4

# ====================================================================================
#  http://www.gnu.org/software/autoconf-archive/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 3 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/>.
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#serial 7

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
])