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+/* vim: set sw=4 sts=4 et foldmethod=syntax : */
+
+/*
+ * Copyright (c) 2006 Ciaran McCreesh <ciaranm@ciaranm.org>
+ *
+ * This file is part of the Paludis package manager. Paludis is free software;
+ * you can redistribute it and/or modify it under the terms of the GNU General
+ * Public License version 2, as published by the Free Software Foundation.
+ *
+ * Paludis 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., 59 Temple
+ * Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#ifndef PALUDIS_GUARD_PALUDIS_UTIL_RANDOM_HH
+#define PALUDIS_GUARD_PALUDIS_UTIL_RANDOM_HH 1
+
+#include <cstdlib>
+#include <inttypes.h>
+#include <paludis/util/attributes.hh>
+
+namespace paludis
+{
+ /**
+ * A basic random number generator class, which is not suitable for
+ * cryptography but is fast and reasonably pseudorandom.
+ *
+ * See \ref TCppPL 22.7 for justification. See \ref TaoCP2 3.2.1 for the
+ * basic algorithm and \ref AppCrypt 16.1 for the choice of numbers.
+ *
+ * \ingroup grprandom
+ */
+ class PALUDIS_VISIBLE Random
+ {
+ private:
+ static uint32_t global_seed;
+ uint32_t local_seed;
+
+ static const uint32_t _a = 2416;
+ static const uint32_t _b = 374441;
+ static const uint32_t _m = 1771875;
+
+ public:
+ ///\name Basic operations
+ ///\{
+
+ /// Constructor, with a seed.
+ Random(uint32_t seed);
+
+ /// Constructor, with a magic random seed.
+ Random();
+
+ ///\}
+
+ /// Fetch a random number in (0, max]
+ template <typename DiffType_>
+ DiffType_ operator() (DiffType_ max)
+ {
+ local_seed = (_a * local_seed + _b) % _m;
+ double t(static_cast<double>(local_seed) / static_cast<double>(_m));
+ return static_cast<DiffType_>(t * max);
+ }
+ };
+}
+
+#endif