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Diffstat (limited to 'm4/align.m4')
| -rw-r--r-- | m4/align.m4 | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/m4/align.m4 b/m4/align.m4 new file mode 100644 index 0000000..733afa6 --- /dev/null +++ b/m4/align.m4 @@ -0,0 +1,32 @@ +# align.m4 +dnl Copyright (C) 2008 Christian Grothoff +dnl This file is free software, distributed under the terms of the GNU +dnl General Public License. As a special exception to the GNU General +dnl Public License, this file may be distributed as part of a program +dnl that contains a configuration script generated by Autoconf, under +dnl the same distribution terms as the rest of that program. + +# Define HAVE_UNALIGNED_64_ACCESS if reading a 64-bit value at a 32-bit aligned offset works +# Note that the program intentionally causes a SIGBUS (so you may +# see some message along those lines on the console). +AC_DEFUN([AC_UNALIGNED_64_ACCESS], +[AC_CACHE_CHECK([whether unaligned 64-bit access works], + ac_cv_unaligned_64_access, + [ + AC_RUN_IFELSE(AC_LANG_PROGRAM([[struct S { int a,b,c;};]], + [[struct S s = {0,0,0}; long long * p = (long long *) &s.b; + void *bp = malloc (50); + long long x = *p; + long long *be = (long long*) &bp[1]; + long long y = *be; + return (int) x*y;]]), + ac_cv_unaligned_64_access=yes, + ac_cv_unaligned_64_access=no, + ac_cv_unaligned_64_access=no) + ]) + case "$ac_cv_unaligned_64_access" in + *yes) value=1;; + *) value=0;; + esac + AC_DEFINE_UNQUOTED([HAVE_UNALIGNED_64_ACCESS], $value, [We can access-64 bit values that are only 32-bit aligned]) +]) |