# random_number.h

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    00001 // -*- C++ -*-
    00002
    00003 // Copyright (C) 2007, 2008 Free Software Foundation, Inc.
    00004 //
    00005 // This file is part of the GNU ISO C++ Library.  This library is free
    00006 // software; you can redistribute it and/or modify it under the terms
    00007 // of the GNU General Public License as published by the Free Software
    00008 // Foundation; either version 2, or (at your option) any later
    00009 // version.
    00010
    00011 // This library is distributed in the hope that it will be useful, but
    00012 // WITHOUT ANY WARRANTY; without even the implied warranty of
    00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    00014 // General Public License for more details.
    00015
    00016 // You should have received a copy of the GNU General Public License
    00017 // along with this library; see the file COPYING.  If not, write to
    00018 // the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
    00019 // MA 02111-1307, USA.
    00020
    00021 // As a special exception, you may use this file as part of a free
    00022 // software library without restriction.  Specifically, if other files
    00023 // instantiate templates or use macros or inline functions from this
    00024 // file, or you compile this file and link it with other files to
    00025 // produce an executable, this file does not by itself cause the
    00026 // resulting executable to be covered by the GNU General Public
    00027 // License.  This exception does not however invalidate any other
    00028 // reasons why the executable file might be covered by the GNU General
    00029 // Public License.
    00030
    00031 /** @file parallel/random_number.h
    00032  *  @brief Random number generator based on the Mersenne twister.
    00033  *  This file is a GNU parallel extension to the Standard C++ Library.
    00034  */
    00035
    00036 // Written by Johannes Singler.
    00037
    00038 #ifndef _GLIBCXX_PARALLEL_RANDOM_NUMBER_H
    00039 #define _GLIBCXX_PARALLEL_RANDOM_NUMBER_H 1
    00040
    00041 #include <parallel/types.h>
    00042 #include <tr1/random>
    00043
    00044 namespace __gnu_parallel
    00045 {
    00046   /** @brief Random number generator, based on the Mersenne twister. */
    00047   class random_number
    00048   {
    00049   private:
    00050     std::tr1::mt19937   mt;
    00051     uint64      supremum;
    00052     uint64      RAND_SUP;
    00053     double      supremum_reciprocal;
    00054     double      RAND_SUP_REC;
    00055
    00056     // Assumed to be twice as long as the usual random number.
    00057     uint64      cache;
    00058
    00059     // Bit results.
    00060     int bits_left;
    00061
    00062     static uint32
    00063     scale_down(uint64 x,
    00064 #if _GLIBCXX_SCALE_DOWN_FPU
    00065            uint64 /*supremum*/, double supremum_reciprocal)
    00066 #else
    00067                uint64 supremum, double /*supremum_reciprocal*/)
    00068 #endif
    00069     {
    00070 #if _GLIBCXX_SCALE_DOWN_FPU
    00071       return uint32(x * supremum_reciprocal);
    00072 #else
    00073       return static_cast<uint32>(x % supremum);
    00074 #endif
    00075     }
    00076
    00077   public:
    00078     /** @brief Default constructor. Seed with 0. */
    00079     random_number()
    00080     : mt(0), supremum(0x100000000ULL),
    00081       RAND_SUP(1ULL << (sizeof(uint32) * 8)),
    00082       supremum_reciprocal(double(supremum) / double(RAND_SUP)),
    00083       RAND_SUP_REC(1.0 / double(RAND_SUP)),
    00084       cache(0), bits_left(0) { }
    00085
    00086     /** @brief Constructor.
    00087      *  @param seed Random seed.
    00088      *  @param supremum Generate integer random numbers in the
    00089      *                  interval @c [0,supremum). */
    00090     random_number(uint32 seed, uint64 supremum = 0x100000000ULL)
    00091     : mt(seed), supremum(supremum),
    00092       RAND_SUP(1ULL << (sizeof(uint32) * 8)),
    00093       supremum_reciprocal(double(supremum) / double(RAND_SUP)),
    00094       RAND_SUP_REC(1.0 / double(RAND_SUP)),
    00095       cache(0), bits_left(0) { }
    00096
    00097     /** @brief Generate unsigned random 32-bit integer. */
    00098     uint32
    00099     operator()()
    00100     { return scale_down(mt(), supremum, supremum_reciprocal); }
    00101
    00102     /** @brief Generate unsigned random 32-bit integer in the
    00103     interval @c [0,local_supremum). */
    00104     uint32
    00105     operator()(uint64 local_supremum)
    00106     {
    00107       return scale_down(mt(), local_supremum,
    00108             double(local_supremum * RAND_SUP_REC));
    00109     }
    00110
    00111     /** @brief Generate a number of random bits, run-time parameter.
    00112      *  @param bits Number of bits to generate. */
    00113     unsigned long
    00114     genrand_bits(int bits)
    00115     {
    00116       unsigned long res = cache & ((1 << bits) - 1);
    00117       cache = cache >> bits;
    00118       bits_left -= bits;
    00119       if (bits_left < 32)
    00120     {
    00121       cache |= ((uint64(mt())) << bits_left);
    00122       bits_left += 32;
    00123     }
    00124       return res;
    00125     }
    00126 };
    00127
    00128 } // namespace __gnu_parallel
    00129
    00130 #endif