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1# align.m4
2dnl Copyright (C) 2008 Christian Grothoff
3dnl This file is free software, distributed under the terms of the GNU
4dnl General Public License. As a special exception to the GNU General
5dnl Public License, this file may be distributed as part of a program
6dnl that contains a configuration script generated by Autoconf, under
7dnl the same distribution terms as the rest of that program.
8
9# Define HAVE_UNALIGNED_64_ACCESS if reading a 64-bit value at a 32-bit aligned offset works
10# Note that the program intentionally causes a SIGBUS (so you may
11# see some message along those lines on the console).
12AC_DEFUN([AC_UNALIGNED_64_ACCESS],
13[AC_CACHE_CHECK([whether unaligned 64-bit access works],
14 ac_cv_unaligned_64_access,
15 [
16 AC_RUN_IFELSE([AC_LANG_PROGRAM([[struct S { int a,b,c;};]],
17 [[struct S s = {0,0,0}; long long * p = (long long *) &s.b;
18 void *bp = malloc (50);
19 long long x = *p;
20 long long *be = (long long*) &bp[1];
21 long long y = *be;
22 return (int) x*y;]])],
23 ac_cv_unaligned_64_access=yes,
24 ac_cv_unaligned_64_access=no,
25 ac_cv_unaligned_64_access=no)
26 ])
27 case "$ac_cv_unaligned_64_access" in
28 *yes) value=1;;
29 *) value=0;;
30 esac
31 AC_DEFINE_UNQUOTED([HAVE_UNALIGNED_64_ACCESS], $value, [We can access-64 bit values that are only 32-bit aligned])
32])