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      1 // -*- C++ -*-
      2 
      3 // Copyright (C) 2007-2013 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 #include <limits>
     38 
     39 namespace __gnu_parallel
     40 {
     41   /** @brief Random number generator, based on the Mersenne twister. */
     42   class _RandomNumber
     43   {
     44   private:
     45     std::tr1::mt19937   _M_mt;
     46     uint64_t            _M_supremum;
     47     uint64_t            _M_rand_sup;
     48     double              _M_supremum_reciprocal;
     49     double              _M_rand_sup_reciprocal;
     50 
     51     // Assumed to be twice as long as the usual random number.
     52     uint64_t              __cache;
     53 
     54     // Bit results.
     55     int __bits_left;
     56 
     57     static uint32_t
     58     __scale_down(uint64_t __x,
     59 #if _GLIBCXX_SCALE_DOWN_FPU
     60                uint64_t /*_M_supremum*/, double _M_supremum_reciprocal)
     61 #else
     62                uint64_t _M_supremum, double /*_M_supremum_reciprocal*/)
     63 #endif
     64         {
     65 #if _GLIBCXX_SCALE_DOWN_FPU
     66           return uint32_t(__x * _M_supremum_reciprocal);
     67 #else
     68           return static_cast<uint32_t>(__x % _M_supremum);
     69 #endif
     70         }
     71 
     72   public:
     73     /** @brief Default constructor. Seed with 0. */
     74     _RandomNumber()
     75     : _M_mt(0), _M_supremum(0x100000000ULL),
     76       _M_rand_sup(1ULL << std::numeric_limits<uint32_t>::digits),
     77       _M_supremum_reciprocal(double(_M_supremum) / double(_M_rand_sup)),
     78       _M_rand_sup_reciprocal(1.0 / double(_M_rand_sup)),
     79       __cache(0), __bits_left(0) { }
     80 
     81     /** @brief Constructor.
     82      *  @param __seed Random __seed.
     83      *  @param _M_supremum Generate integer random numbers in the
     84      *                  interval @c [0,_M_supremum). */
     85     _RandomNumber(uint32_t __seed, uint64_t _M_supremum = 0x100000000ULL)
     86     : _M_mt(__seed), _M_supremum(_M_supremum),
     87       _M_rand_sup(1ULL << std::numeric_limits<uint32_t>::digits),
     88       _M_supremum_reciprocal(double(_M_supremum) / double(_M_rand_sup)),
     89       _M_rand_sup_reciprocal(1.0 / double(_M_rand_sup)),
     90       __cache(0), __bits_left(0) { }
     91 
     92     /** @brief Generate unsigned random 32-bit integer. */
     93     uint32_t
     94     operator()()
     95     { return __scale_down(_M_mt(), _M_supremum, _M_supremum_reciprocal); }
     96 
     97     /** @brief Generate unsigned random 32-bit integer in the
     98         interval @c [0,local_supremum). */
     99     uint32_t
    100     operator()(uint64_t local_supremum)
    101     {
    102       return __scale_down(_M_mt(), local_supremum,
    103                         double(local_supremum * _M_rand_sup_reciprocal));
    104     }
    105 
    106     /** @brief Generate a number of random bits, run-time parameter.
    107      *  @param __bits Number of bits to generate. */
    108     unsigned long
    109     __genrand_bits(int __bits)
    110     {
    111       unsigned long __res = __cache & ((1 << __bits) - 1);
    112       __cache = __cache >> __bits;
    113       __bits_left -= __bits;
    114       if (__bits_left < 32)
    115         {
    116           __cache |= ((uint64_t(_M_mt())) << __bits_left);
    117           __bits_left += 32;
    118         }
    119       return __res;
    120     }
    121 };
    122 
    123 } // namespace __gnu_parallel
    124 
    125 #endif /* _GLIBCXX_PARALLEL_RANDOM_NUMBER_H */
    126