mingw/lib/gcc/mingw32/4.3.3/include/c++/parallel/random_number.h

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2007, 2008 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the terms
   7 // of the GNU General Public License as published by the Free Software
   8 // Foundation; either version 2, or (at your option) any later
   9 // version.
  10
  11 // This library is distributed in the hope that it will be useful, but
  12 // WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 // General Public License for more details.
  15
  16 // You should have received a copy of the GNU General Public License
  17 // along with this library; see the file COPYING.  If not, write to
  18 // the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
  19 // MA 02111-1307, USA.
  20
  21 // As a special exception, you may use this file as part of a free
  22 // software library without restriction.  Specifically, if other files
  23 // instantiate templates or use macros or inline functions from this
  24 // file, or you compile this file and link it with other files to
  25 // produce an executable, this file does not by itself cause the
  26 // resulting executable to be covered by the GNU General Public
  27 // License.  This exception does not however invalidate any other
  28 // reasons why the executable file might be covered by the GNU General
  29 // Public License.
  30
  31 /** @file parallel/random_number.h
  32  *  @brief Random number generator based on the Mersenne twister.
  33  *  This file is a GNU parallel extension to the Standard C++ Library.
  34  */
  35
  36 // Written by Johannes Singler.
  37
  38 #ifndef _GLIBCXX_PARALLEL_RANDOM_NUMBER_H
  39 #define _GLIBCXX_PARALLEL_RANDOM_NUMBER_H 1
  40
  41 #include <parallel/types.h>
  42 #include <tr1/random>
  43
  44 namespace __gnu_parallel
  45 {
  46   /** @brief Random number generator, based on the Mersenne twister. */
  47   class random_number
  48   {
  49   private:
  50     std::tr1::mt19937   mt;
  51     uint64              supremum;
  52     uint64              RAND_SUP;
  53     double              supremum_reciprocal;
  54     double              RAND_SUP_REC;
  55
  56     // Assumed to be twice as long as the usual random number.
  57     uint64              cache;
  58
  59     // Bit results.
  60     int bits_left;
  61
  62     static uint32
  63     scale_down(uint64 x,
  64 #if _GLIBCXX_SCALE_DOWN_FPU
  65                uint64 /*supremum*/, double supremum_reciprocal)
  66 #else
  67                uint64 supremum, double /*supremum_reciprocal*/)
  68 #endif
  69         {
  70 #if _GLIBCXX_SCALE_DOWN_FPU
  71           return uint32(x * supremum_reciprocal);
  72 #else
  73           return static_cast<uint32>(x % supremum);
  74 #endif
  75         }
  76
  77   public:
  78     /** @brief Default constructor. Seed with 0. */
  79     random_number()
  80     : mt(0), supremum(0x100000000ULL),
  81       RAND_SUP(1ULL << (sizeof(uint32) * 8)),
  82       supremum_reciprocal(double(supremum) / double(RAND_SUP)),
  83       RAND_SUP_REC(1.0 / double(RAND_SUP)),
  84       cache(0), bits_left(0) { }
  85
  86     /** @brief Constructor.
  87      *  @param seed Random seed.
  88      *  @param supremum Generate integer random numbers in the
  89      *                  interval @c [0,supremum). */
  90     random_number(uint32 seed, uint64 supremum = 0x100000000ULL)
  91     : mt(seed), supremum(supremum),
  92       RAND_SUP(1ULL << (sizeof(uint32) * 8)),
  93       supremum_reciprocal(double(supremum) / double(RAND_SUP)),
  94       RAND_SUP_REC(1.0 / double(RAND_SUP)),
  95       cache(0), bits_left(0) { }
  96
  97     /** @brief Generate unsigned random 32-bit integer. */
  98     uint32
  99     operator()()
 100     { return scale_down(mt(), supremum, supremum_reciprocal); }
 101
 102     /** @brief Generate unsigned random 32-bit integer in the
 103         interval @c [0,local_supremum). */
 104     uint32
 105     operator()(uint64 local_supremum)
 106     {
 107       return scale_down(mt(), local_supremum,
 108                         double(local_supremum * RAND_SUP_REC));
 109     }
 110
 111     /** @brief Generate a number of random bits, run-time parameter.
 112      *  @param bits Number of bits to generate. */
 113     unsigned long
 114     genrand_bits(int bits)
 115     {
 116       unsigned long res = cache & ((1 << bits) - 1);
 117       cache = cache >> bits;
 118       bits_left -= bits;
 119       if (bits_left < 32)
 120         {
 121           cache |= ((uint64(mt())) << bits_left);
 122           bits_left += 32;
 123         }
 124       return res;
 125     }
 126 };
 127
 128 } // namespace __gnu_parallel
 129
 130 #endif