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// -*- C++ -*-

// Copyright (C) 2007, 2008, 2009 Free Software Foundation, Inc.

//

// This file is part of the GNU ISO C++ Library.  This library is free

// software; you can redistribute it and/or modify it under the terms

// of the GNU General Public License as published by the Free Software

// Foundation; either version 3, or (at your option) any later

// version.

// This library is distributed in the hope that it will be useful, but

// WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

// General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional

// permissions described in the GCC Runtime Library Exception, version

// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and

// a copy of the GCC Runtime Library Exception along with this program;

// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see

// <http://www.gnu.org/licenses/>.

/** @file parallel/random_number.h

 *  @brief Random number generator based on the Mersenne twister.

 *  This file is a GNU parallel extension to the Standard C++ Library.

 */

// Written by Johannes Singler.

#ifndef _GLIBCXX_PARALLEL_RANDOM_NUMBER_H

#define _GLIBCXX_PARALLEL_RANDOM_NUMBER_H 1

#include <parallel/types.h>

#include <tr1/random>

#include <limits>

namespace __gnu_parallel

{

  /** @brief Random number generator, based on the Mersenne twister. */

  class _RandomNumber

  {

  private:

    std::tr1::mt19937   _M_mt;

    uint64_t            _M_supremum;

    uint64_t            _M_rand_sup;

    double              _M_supremum_reciprocal;

    double              _M_rand_sup_reciprocal;

    // Assumed to be twice as long as the usual random number.

    uint64_t              __cache;

    // Bit results.

    int __bits_left;

    static uint32_t

    __scale_down(uint64_t __x,

#if _GLIBCXX_SCALE_DOWN_FPU

               uint64_t /*_M_supremum*/, double _M_supremum_reciprocal)

#else

               uint64_t _M_supremum, double /*_M_supremum_reciprocal*/)

#endif

        {

#if _GLIBCXX_SCALE_DOWN_FPU

          return uint32_t(__x * _M_supremum_reciprocal);

#else

          return static_cast<uint32_t>(__x % _M_supremum);

#endif

        }

  public:

    /** @brief Default constructor. Seed with 0. */

    _RandomNumber()

    : _M_mt(0), _M_supremum(0x100000000ULL),

      _M_rand_sup(1ULL << std::numeric_limits<uint32_t>::digits),

      _M_supremum_reciprocal(double(_M_supremum) / double(_M_rand_sup)),

      _M_rand_sup_reciprocal(1.0 / double(_M_rand_sup)),

      __cache(0), __bits_left(0) { }

    /** @brief Constructor.

     *  @param __seed Random __seed.

     *  @param _M_supremum Generate integer random numbers in the

     *                  interval @c [0,_M_supremum). */

    _RandomNumber(uint32_t __seed, uint64_t _M_supremum = 0x100000000ULL)

    : _M_mt(__seed), _M_supremum(_M_supremum),

      _M_rand_sup(1ULL << std::numeric_limits<uint32_t>::digits),

      _M_supremum_reciprocal(double(_M_supremum) / double(_M_rand_sup)),

      _M_rand_sup_reciprocal(1.0 / double(_M_rand_sup)),

      __cache(0), __bits_left(0) { }

    /** @brief Generate unsigned random 32-bit integer. */

    uint32_t

    operator()()

    { return __scale_down(_M_mt(), _M_supremum, _M_supremum_reciprocal); }

    /** @brief Generate unsigned random 32-bit integer in the

        interval @c [0,local_supremum). */

    uint32_t

    operator()(uint64_t local_supremum)

    {

      return __scale_down(_M_mt(), local_supremum,

                        double(local_supremum * _M_rand_sup_reciprocal));

    }

    /** @brief Generate a number of random bits, run-time parameter.

     *  @param bits Number of bits to generate. */

    unsigned long

    __genrand_bits(int __bits)

    {

      unsigned long __res = __cache & ((1 << __bits) - 1);

      __cache = __cache >> __bits;

      __bits_left -= __bits;

      if (__bits_left < 32)

        {

          __cache |= ((uint64_t(_M_mt())) << __bits_left);

          __bits_left += 32;

        }

      return __res;

    }

};

} // namespace __gnu_parallel

#endif /* _GLIBCXX_PARALLEL_RANDOM_NUMBER_H */