text: /* boost random/geometric_distribution.hpp header file
   *
   * Copyright Jens Maurer 2000-2001
   * Copyright Steven Watanabe 2011
   * 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 71018 2011-04-05 21:27:52Z steven_watanabe $
   *
   * Revision history
   *  2001-02-18  moved to individual header files
   */
  
  #ifndef BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
  #define BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
  
  #include <boost/config/no_tr1/cmath.hpp>          // std::log
  #include <iosfwd>
  #include <ios>
  #include <boost/assert.hpp>
  #include <boost/random/detail/config.hpp>
  #include <boost/random/detail/operators.hpp>
  #include <boost/random/uniform_01.hpp>
  
  namespace boost {
  namespace random {
  
  /**
   * An instantiation of the class template @c geometric_distribution models
   * a \random_distribution.  The distribution produces positive
   * integers which are the number of bernoulli trials
   * with probability @c p required to get one that fails.
   *
   * For the geometric distribution, \f$p(i) = p(1-p)^{i}\f$.
   *
   * @xmlwarning
   * This distribution has been updated to match the C++ standard.
   * Its behavior has changed from the original
   * boost::geometric_distribution.  A backwards compatible
   * wrapper is provided in namespace boost.
   * @endxmlwarning
   */
  template<class IntType = int, class RealType = double>
  class geometric_distribution
  {
  public:
      typedef RealType input_type;
      typedef IntType result_type;
  
      class param_type
      {
      public:
  
          typedef geometric_distribution distribution_type;
  
          /** Constructs the parameters with p. */
          explicit param_type(RealType p_arg = RealType(0.5))
            : _p(p_arg)
          {
              BOOST_ASSERT(RealType(0) < _p && _p < RealType(1));
          }
  
          /** Returns the p parameter of the distribution. */
          RealType p() const { return _p; }
  
          /** Writes the parameters to a std::ostream. */
          BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, param_type, parm)
          {
              os << parm._p;
              return os;
          }
  
          /** Reads the parameters from a std::istream. */
          BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, param_type, parm)
          {
              double p_in;
              if(is >> p_in) {
                  if(p_in > RealType(0) && p_in < RealType(1)) {
                      parm._p = p_in;
                  } else {
                      is.setstate(std::ios_base::failbit);
                  }
              }
              return is;
          }
  
          /** Returns true if the two sets of parameters are equal. */
          BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(param_type, lhs, rhs)
          { return lhs._p == rhs._p; }
  
          /** Returns true if the two sets of parameters are different. */
          BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(param_type)
  
  
      private:
          RealType _p;
      };
  
      /**
       * Contructs a new geometric_distribution with the paramter @c p.
       *
       * Requires: 0 < p < 1
       */
      explicit geometric_distribution(const RealType& p = RealType(0.5))
        : _p(p)
      {
          BOOST_ASSERT(RealType(0) < _p && _p < RealType(1));
          init();
      }
  
      /** Constructs a new geometric_distribution from its parameters. */
      explicit geometric_distribution(const param_type& parm)
        : _p(parm.p())
      {
          init();
      }
  
      // compiler-generated copy ctor and assignment operator are fine
  
      /** Returns: the distribution parameter @c p  */
      RealType p() const { return _p; }
  
      /** Returns the smallest value that the distribution can produce. */
      IntType min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return IntType(1); }
  
      /** Returns the largest value that the distribution can produce. */
      IntType max BOOST_PREVENT_MACRO_SUBSTITUTION () const
      { return (std::numeric_limits<IntType>::max)(); }
  
      /** Returns the parameters of the distribution. */
      param_type param() const { return param_type(_p); }
  
      /** Sets the parameters of the distribution. */
      void param(const param_type& parm)
      {
          _p = parm.p();
          init();
      }
    
      /**
       * Effects: Subsequent uses of the distribution do not depend
       * on values produced by any engine prior to invoking reset.
       */
      void reset() { }
  
      /**
       * Returns a random variate distributed according to the
       * geometric_distribution.
       */
      template<class Engine>
      result_type operator()(Engine& eng) const
      {
          using std::log;
          using std::floor;
          RealType x = RealType(1) - boost::uniform_01<RealType>()(eng);
          return IntType(floor(log(x) / _log_1mp));
      }
  
      /**
       * Returns a random variate distributed according to the
       * geometric distribution with parameters specified by param.
       */
      template<class Engine>
      result_type operator()(Engine& eng, const param_type& parm) const
      { return geometric_distribution(parm)(eng); }
  
      /** Writes the distribution to a @c std::ostream. */
      BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, geometric_distribution, gd)
      {
          os << gd._p;
          return os;
      }
  
      /** Reads the distribution from a @c std::istream. */
      BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, geometric_distribution, gd)
      {
          param_type parm;
          if(is >> parm) {
              gd.param(parm);
          }
          return is;
      }
  
      /**
       * Returns true if the two distributions will produce identical
       * sequences of values given equal generators.
       */
      BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(geometric_distribution, lhs, rhs)
      { return lhs._p == rhs._p; }
  
      /**
       * Returns true if the two distributions may produce different
       * sequences of values given equal generators.
       */
      BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(geometric_distribution)
  
  private:
  
      /// \cond show_private
  
      void init()
      {
          using std::log;
          _log_1mp = log(1 - _p);
      }
  
      RealType _p;
      RealType _log_1mp;
  
      /// \endcond
  };
  
  } // namespace random
  
  /// \cond show_deprecated
  
  /**
   * Provided for backwards compatibility.  This class is
   * deprecated.  It provides the old behavior of geometric_distribution
   * with \f$p(i) = (1-p) p^{i-1}\f$.
   */
  template<class IntType = int, class RealType = double>
  class geometric_distribution
  {
  public:
      typedef RealType input_type;
      typedef IntType result_type;
  
      explicit geometric_distribution(RealType p_arg = RealType(0.5))
        : _impl(1 - p_arg) {}
  
      RealType p() const { return 1 - _impl.p(); }
  
      void reset() {}
  
      template<class Engine>
      IntType operator()(Engine& eng) const { return _impl(eng) + IntType(1); }
  
      BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, geometric_distribution, gd)
      {
          os << gd.p();
          return os;
      }
  
      BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, geometric_distribution, gd)
      {
          RealType val;
          if(is >> val) {
              typename impl_type::param_type impl_param(1 - val);
              gd._impl.param(impl_param);
          }
          return is;
      }
  
  private:
      typedef random::geometric_distribution<IntType, RealType> impl_type;
      impl_type _impl;
  };
  
  /// \endcond
  
  } // namespace boost
  
  #endif // BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
  