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Autoconf Macro: ax_check_aligned_access_required
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<h1>
ax_check_aligned_access_required
</h1>
<h2>
Synopsis
</h2>
<p class="indent" style="white-space:nowrap;">
<code>AC_CHECK_ALIGNED_ACCESS_REQUIRED</code>
</p>
<h2>
Description
</h2>
<div class="indent">
<p>
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.
</p>
<p>
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.
</p>
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<h2>
Author
</h2>
<p class="indent">
Guido U. Draheim <guidod@gmx.de>
</p>
<h2>
Last Modified
</h2>
<p class="indent">
2006-08-17
</p>
<h2>
M4 Source Code
</h2>
<div class="indent">
<pre class="m4source">
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
])
</pre>
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<h2>
License
</h2>
<div class="indent">
<span style="white-space:nowrap;">Copyright © 2006 Guido U. Draheim
<guidod@gmx.de></span>
<p>
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.
</p>
<p>
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.
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You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc., 59
Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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use of the material that constitutes the Autoconf Macro.
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