util: added TYPESAFE_QSORT() macro

This makes it much harder to get the type of a qsort comparison
function wrong.

lib/util/tsort.h

@@ -0,0 +1,38 @@
+/*
+   Unix SMB/CIFS implementation.
+
+   typesafe qsort
+
+   Copyright (C) Andrew Tridgell 2010
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef _TSORT_H
+#define _TSORT_H
+#include <assert.h>
+
+/*
+  a wrapper around qsort() that ensures the comparison function is
+  type safe.
+ */
+#define TYPESAFE_QSORT(base, numel, comparison) \
+do { \
+	if (numel > 1) { \
+		qsort(base, numel, sizeof((base)[0]), QSORT_CAST comparison); \
+		assert(comparison(&((base)[0]), &((base)[1])) <= 0); \
+	} \
+} while (0)
+
+#endif