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diff --git a/sntp/m4/ax_c99_struct_init.m4 b/sntp/m4/ax_c99_struct_init.m4
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+++ b/sntp/m4/ax_c99_struct_init.m4
@@ -0,0 +1,59 @@
+# ===========================================================================
+#       http://www.gnu.org/software/autoconf-archive/ax_c99_struct_init.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_C99_STRUCT_INIT
+#
+# DESCRIPTION
+#
+#   This macro defines MISSING_C99_STRUCT_INIT if the C compiler does not
+#   supports the C99 tagged structure initialization.
+#
+#   Given: struct foo_s {int i1; int i2; int i3;};
+#   one can write:
+#	#if !define(MISSING_C99_STRUCT_INIT)
+#	# define FOO_INIT(a, b, c) { .i1 = a, .i2 = b, .i3 = c }
+#	#else
+#	# define FOO_INIT(a, b, c) { a, b, c }
+#
+#	static struct foo_s foo[] = {
+#		FOO_INIT(1, 1, 1),
+#		FOO_INIT(2, 2, 2),
+#		FOO_INIT(0, 0, 0)
+#	};
+#
+# LICENSE
+#
+#   Copyright (c) 2015 Network Time Foundation
+#
+#   Author: Harlan Stenn <stenn@nwtime.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 1
+
+AC_DEFUN([AX_C99_STRUCT_INIT], [
+	AC_MSG_CHECKING([whether the compiler supports C99 structure initialization])
+	AC_REQUIRE([AC_PROG_CC_C99])
+
+	AC_LANG_PUSH([C])
+
+	dnl AC_LINK_IFELSE?
+	AC_COMPILE_IFELSE(
+		[AC_LANG_SOURCE([[
+			struct foo_s {int i1; int i2;};
+			int main() { struct foo_s foo[] = { { .i1 = 1, .i2 = 1 }, { .i1 = 2, .i2 = 2 }, { .i1 = 0, .i2 = 0 } }; }
+			]])],
+		AC_MSG_RESULT([yes]),
+		AC_MSG_RESULT([no])
+		AC_DEFINE([MISSING_C99_STRUCT_INIT], [1],
+			[Define to 1 if the compiler does not support C99's structure initialization.]),
+		)
+
+	AC_LANG_POP([C])
+	]);