# random_number.h

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    00001 // -*- C++ -*-
    00002
    00003 // Copyright (C) 2007, 2008, 2009 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 3, 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 // Under Section 7 of GPL version 3, you are granted additional
    00017 // permissions described in the GCC Runtime Library Exception, version
    00018 // 3.1, as published by the Free Software Foundation.
    00019
    00020 // You should have received a copy of the GNU General Public License and
    00021 // a copy of the GCC Runtime Library Exception along with this program;
    00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    00023 // <http://www.gnu.org/licenses/>.
    00024
    00025 /** @file parallel/random_number.h
    00026  *  @brief Random number generator based on the Mersenne twister.
    00027  *  This file is a GNU parallel extension to the Standard C++ Library.
    00028  */
    00029
    00030 // Written by Johannes Singler.
    00031
    00032 #ifndef _GLIBCXX_PARALLEL_RANDOM_NUMBER_H
    00033 #define _GLIBCXX_PARALLEL_RANDOM_NUMBER_H 1
    00034
    00035 #include <parallel/types.h>
    00036 #include <tr1/random>
    00037
    00038 namespace __gnu_parallel
    00039 {
    00040   /** @brief Random number generator, based on the Mersenne twister. */
    00041   class random_number
    00042   {
    00043   private:
    00044     std::tr1::mt19937   mt;
    00045     uint64      supremum;
    00046     uint64      RAND_SUP;
    00047     double      supremum_reciprocal;
    00048     double      RAND_SUP_REC;
    00049
    00050     // Assumed to be twice as long as the usual random number.
    00051     uint64      cache;
    00052
    00053     // Bit results.
    00054     int bits_left;
    00055
    00056     static uint32
    00057     scale_down(uint64 x,
    00058 #if _GLIBCXX_SCALE_DOWN_FPU
    00059            uint64 /*supremum*/, double supremum_reciprocal)
    00060 #else
    00061                uint64 supremum, double /*supremum_reciprocal*/)
    00062 #endif
    00063     {
    00064 #if _GLIBCXX_SCALE_DOWN_FPU
    00065       return uint32(x * supremum_reciprocal);
    00066 #else
    00067       return static_cast<uint32>(x % supremum);
    00068 #endif
    00069     }
    00070
    00071   public:
    00072     /** @brief Default constructor. Seed with 0. */
    00073     random_number()
    00074     : mt(0), supremum(0x100000000ULL),
    00075       RAND_SUP(1ULL << (sizeof(uint32) * 8)),
    00076       supremum_reciprocal(double(supremum) / double(RAND_SUP)),
    00077       RAND_SUP_REC(1.0 / double(RAND_SUP)),
    00078       cache(0), bits_left(0) { }
    00079
    00080     /** @brief Constructor.
    00081      *  @param seed Random seed.
    00082      *  @param supremum Generate integer random numbers in the
    00083      *                  interval @c [0,supremum). */
    00084     random_number(uint32 seed, uint64 supremum = 0x100000000ULL)
    00085     : mt(seed), supremum(supremum),
    00086       RAND_SUP(1ULL << (sizeof(uint32) * 8)),
    00087       supremum_reciprocal(double(supremum) / double(RAND_SUP)),
    00088       RAND_SUP_REC(1.0 / double(RAND_SUP)),
    00089       cache(0), bits_left(0) { }
    00090
    00091     /** @brief Generate unsigned random 32-bit integer. */
    00092     uint32
    00093     operator()()
    00094     { return scale_down(mt(), supremum, supremum_reciprocal); }
    00095
    00096     /** @brief Generate unsigned random 32-bit integer in the
    00097     interval @c [0,local_supremum). */
    00098     uint32
    00099     operator()(uint64 local_supremum)
    00100     {
    00101       return scale_down(mt(), local_supremum,
    00102             double(local_supremum * RAND_SUP_REC));
    00103     }
    00104
    00105     /** @brief Generate a number of random bits, run-time parameter.
    00106      *  @param bits Number of bits to generate. */
    00107     unsigned long
    00108     genrand_bits(int bits)
    00109     {
    00110       unsigned long res = cache & ((1 << bits) - 1);
    00111       cache = cache >> bits;
    00112       bits_left -= bits;
    00113       if (bits_left < 32)
    00114     {
    00115       cache |= ((uint64(mt())) << bits_left);
    00116       bits_left += 32;
    00117     }
    00118       return res;
    00119     }
    00120 };
    00121
    00122 } // namespace __gnu_parallel
    00123
    00124 #endif /* _GLIBCXX_PARALLEL_RANDOM_NUMBER_H */