contrib/gcc-4.4/libstdc++-v3/include/parallel/random_number.h

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2007, 2008, 2009 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 3, 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 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 /** @file parallel/random_number.h
  26  *  @brief Random number generator based on the Mersenne twister.
  27  *  This file is a GNU parallel extension to the Standard C++ Library.
  28  */
  29
  30 // Written by Johannes Singler.
  31
  32 #ifndef _GLIBCXX_PARALLEL_RANDOM_NUMBER_H
  33 #define _GLIBCXX_PARALLEL_RANDOM_NUMBER_H 1
  34
  35 #include <parallel/types.h>
  36 #include <tr1/random>
  37
  38 namespace __gnu_parallel
  39 {
  40   /** @brief Random number generator, based on the Mersenne twister. */
  41   class random_number
  42   {
  43   private:
  44     std::tr1::mt19937   mt;
  45     uint64              supremum;
  46     uint64              RAND_SUP;
  47     double              supremum_reciprocal;
  48     double              RAND_SUP_REC;
  49
  50     // Assumed to be twice as long as the usual random number.
  51     uint64              cache;
  52
  53     // Bit results.
  54     int bits_left;
  55
  56     static uint32
  57     scale_down(uint64 x,
  58 #if _GLIBCXX_SCALE_DOWN_FPU
  59                uint64 /*supremum*/, double supremum_reciprocal)
  60 #else
  61                uint64 supremum, double /*supremum_reciprocal*/)
  62 #endif
  63         {
  64 #if _GLIBCXX_SCALE_DOWN_FPU
  65           return uint32(x * supremum_reciprocal);
  66 #else
  67           return static_cast<uint32>(x % supremum);
  68 #endif
  69         }
  70
  71   public:
  72     /** @brief Default constructor. Seed with 0. */
  73     random_number()
  74     : mt(0), supremum(0x100000000ULL),
  75       RAND_SUP(1ULL << (sizeof(uint32) * 8)),
  76       supremum_reciprocal(double(supremum) / double(RAND_SUP)),
  77       RAND_SUP_REC(1.0 / double(RAND_SUP)),
  78       cache(0), bits_left(0) { }
  79
  80     /** @brief Constructor.
  81      *  @param seed Random seed.
  82      *  @param supremum Generate integer random numbers in the
  83      *                  interval @c [0,supremum). */
  84     random_number(uint32 seed, uint64 supremum = 0x100000000ULL)
  85     : mt(seed), supremum(supremum),
  86       RAND_SUP(1ULL << (sizeof(uint32) * 8)),
  87       supremum_reciprocal(double(supremum) / double(RAND_SUP)),
  88       RAND_SUP_REC(1.0 / double(RAND_SUP)),
  89       cache(0), bits_left(0) { }
  90
  91     /** @brief Generate unsigned random 32-bit integer. */
  92     uint32
  93     operator()()
  94     { return scale_down(mt(), supremum, supremum_reciprocal); }
  95
  96     /** @brief Generate unsigned random 32-bit integer in the
  97         interval @c [0,local_supremum). */
  98     uint32
  99     operator()(uint64 local_supremum)
 100     {
 101       return scale_down(mt(), local_supremum,
 102                         double(local_supremum * RAND_SUP_REC));
 103     }
 104
 105     /** @brief Generate a number of random bits, run-time parameter.
 106      *  @param bits Number of bits to generate. */
 107     unsigned long
 108     genrand_bits(int bits)
 109     {
 110       unsigned long res = cache & ((1 << bits) - 1);
 111       cache = cache >> bits;
 112       bits_left -= bits;
 113       if (bits_left < 32)
 114         {
 115           cache |= ((uint64(mt())) << bits_left);
 116           bits_left += 32;
 117         }
 118       return res;
 119     }
 120 };
 121
 122 } // namespace __gnu_parallel
 123
 124 #endif /* _GLIBCXX_PARALLEL_RANDOM_NUMBER_H */