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# ===========================================================================
# https://www.gnu.org/software/autoconf-archive/ax_c_restrict.html
# ===========================================================================
#
# SYNOPSIS
#
# AX_C_RESTRICT
#
# DESCRIPTION
#
# This macro checks if the C99 restrict keyword is broken with the current
# compiler and optimizations settings. If broken, it undefines restrict to
# do no harm. As of 2019 gcc since 5.0 and clang since 6.0 (June 2017) are
# known to be broken and not yet fixed. See
# https://github.com/rust-lang/rust/issues/54878 with the links to the gcc
# and clang tickets.
#
# LICENSE
#
# Copyright (c) 2019 Reini Urban <rurban@cpan.org>
#
# Copying and distribution of this file, with or without modification, are
# permitted in any medium without royalty provided the copyright notice
# and this notice are preserved. This file is offered as-is, without any
# warranty.
#serial 2
AC_DEFUN([AX_C_RESTRICT],
[AC_CACHE_CHECK([for restrict usability],
[ax_cv_c_restrict_usable],
[AC_RUN_IFELSE([AC_LANG_PROGRAM([],
[[
void copy (int * restrict to, int * restrict from) {
*to = *from;
}
void test (int *a, int *b) {
for (int i = 0; i < 4; i++) {
copy (&b[i & 1], &a[i & 1]);
}
}
int main () {
int ary[] = {0, 1, 2};
test (&ary[1], &ary[0]);
/* printf("%d %d %d\n", ary[0], ary[1], ary[2]);
2 2 2 is correct
1 2 2 wrong */
return ary[0] == 2 ? 0 : 1;
}
]])],
[ax_cv_c_restrict_usable=restrict],
[ax_cv_c_restrict_usable=],
[ax_cv_c_restrict_usable=])])
if test -z $ax_cv_c_restrict_usable; then
AC_MSG_RESULT([no])
AC_DEFINE_UNQUOTED(restrict, $ax_cv_c_restrict_usable,
[If restrict is broken with this C compiler])
else
AC_MSG_RESULT([yes])
fi
]) dnl AX_C_RESTRICT
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