/* boost random/geometric_distribution.hpp header file

 *

 * Copyright Jens Maurer 2000-2001

 * Distributed under the Boost Software License, Version 1.0. (See

 * accompanying file LICENSE_1_0.txt or copy at

 * http://www.boost.org/LICENSE_1_0.txt)

 *

 * See http://www.boost.org for most recent version including documentation.

 *

 * $Id: geometric_distribution.hpp,v 1.16 2004/07/27 03:43:32 dgregor Exp $

 *

 * Revision history

 *  2001-02-18  moved to individual header files

 */

#ifndef BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP

#define BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP

#include <cmath>          // std::log

#include <cassert>

#include <iostream>

#include <boost/random/uniform_01.hpp>

namespace boost {

#if defined(__GNUC__) && (__GNUC__ < 3)

// Special gcc workaround: gcc 2.95.x ignores using-declarations

// in template classes (confirmed by gcc author Martin v. Loewis)

  using std::log;

#endif

// geometric distribution: p(i) = (1-p) * pow(p, i-1)   (integer)

template<class IntType = int, class RealType = double>

class geometric_distribution

{

public:

  typedef RealType input_type;

  typedef IntType result_type;

  explicit geometric_distribution(const RealType& p = RealType(0.5))

    : _p(p)

  {

    assert(RealType(0) < p && p < RealType(1));

    init();

  }

  // compiler-generated copy ctor and assignment operator are fine

  RealType p() const { return _p; }

  void reset() { }

  template<class Engine>

  result_type operator()(Engine& eng)

  {

#ifndef BOOST_NO_STDC_NAMESPACE

    using std::log;

    using std::floor;

#endif

    return IntType(floor(log(RealType(1)-eng()) / _log_p)) + IntType(1);

  }

#if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)

  template<class CharT, class Traits>

  friend std::basic_ostream<CharT,Traits>&

  operator<<(std::basic_ostream<CharT,Traits>& os, const geometric_distribution& gd)

  {

    os << gd._p;

    return os;

  }

  template<class CharT, class Traits>

  friend std::basic_istream<CharT,Traits>&

  operator>>(std::basic_istream<CharT,Traits>& is, geometric_distribution& gd)

  {

    is >> std::ws >> gd._p;

    gd.init();

    return is;

  }

#endif

private:

  void init()

  {

#ifndef BOOST_NO_STDC_NAMESPACE

    using std::log;

#endif

    _log_p = log(_p);

  }

  RealType _p;

  RealType _log_p;

};

} // namespace boost

#endif // BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP