random.hh

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00001 /* vim: set sw=4 sts=4 et foldmethod=syntax : */
00002 
00003 /*
00004  * Copyright (c) 2006, 2007, 2008, 2009 Ciaran McCreesh
00005  *
00006  * This file is part of the Paludis package manager. Paludis is free software;
00007  * you can redistribute it and/or modify it under the terms of the GNU General
00008  * Public License version 2, as published by the Free Software Foundation.
00009  *
00010  * Paludis is distributed in the hope that it will be useful, but WITHOUT ANY
00011  * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
00012  * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
00013  * details.
00014  *
00015  * You should have received a copy of the GNU General Public License along with
00016  * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
00017  * Place, Suite 330, Boston, MA  02111-1307  USA
00018  */
00019 
00020 #ifndef PALUDIS_GUARD_PALUDIS_UTIL_RANDOM_HH
00021 #define PALUDIS_GUARD_PALUDIS_UTIL_RANDOM_HH 1
00022 
00023 #include <cstdlib>
00024 #include <inttypes.h>
00025 #include <paludis/util/attributes.hh>
00026 
00027 /** \file
00028  * Declarations for the Random class.
00029  *
00030  * \ingroup g_utils
00031  *
00032  * \section Examples
00033  *
00034  * - None at this time.
00035  */
00036 
00037 namespace paludis
00038 {
00039     /**
00040      * A basic random number generator class, which is not suitable for
00041      * cryptography but is fast and reasonably pseudorandom.
00042      *
00043      * See \ref TCppPL 22.7 for justification. See \ref TaoCP2 3.2.1 for the
00044      * basic algorithm and \ref AppCrypt 16.1 for the choice of numbers.
00045      *
00046      * \ingroup g_utils
00047      * \nosubgrouping
00048      */
00049     class PALUDIS_VISIBLE Random
00050     {
00051         private:
00052             static uint32_t global_seed;
00053             uint32_t local_seed;
00054 
00055             static const uint32_t _a = 2416;
00056             static const uint32_t _b = 374441;
00057             static const uint32_t _m = 1771875;
00058 
00059         public:
00060             ///\name Basic operations
00061             ///\{
00062 
00063             /// Constructor, with a seed.
00064             Random(uint32_t seed);
00065 
00066             /// Constructor, with a magic random seed.
00067             Random();
00068 
00069             ///\}
00070 
00071             /// Fetch a random number in (0, max]
00072             template <typename DiffType_>
00073             DiffType_ operator() (DiffType_ max)
00074             {
00075                 local_seed = (_a * local_seed + _b) % _m;
00076                 double t(static_cast<double>(local_seed) / static_cast<double>(_m));
00077                 return static_cast<DiffType_>(t * max);
00078             }
00079     };
00080 }
00081 
00082 #endif

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