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+/*
+ * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_LAZY_RANDOM_ENGINE_HXX
+#define MPD_LAZY_RANDOM_ENGINE_HXX
+
+#include "check.h"
+
+#include <random>
+
+#include <assert.h>
+
+/**
+ * A random engine that will be created and seeded on demand.
+ */
+class LazyRandomEngine {
+ std::mt19937 *engine;
+
+public:
+ typedef std::mt19937::result_type result_type;
+
+ LazyRandomEngine():engine(nullptr) {}
+ ~LazyRandomEngine() {
+ delete engine;
+ }
+
+ LazyRandomEngine(const LazyRandomEngine &other) = delete;
+ LazyRandomEngine &operator=(const LazyRandomEngine &other) = delete;
+
+ /**
+ * Create and seed the real engine. Call this before any
+ * other method.
+ */
+ void AutoCreate();
+
+ result_type min() const {
+ return engine->min();
+ }
+
+ result_type max() const {
+ return engine->max();
+ }
+
+ result_type operator()() {
+ assert(engine != nullptr);
+
+ return engine->operator()();
+ }
+};
+
+#endif