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