williamr@2: /* boost random/geometric_distribution.hpp header file
williamr@2:  *
williamr@2:  * Copyright Jens Maurer 2000-2001
williamr@2:  * Distributed under the Boost Software License, Version 1.0. (See
williamr@2:  * accompanying file LICENSE_1_0.txt or copy at
williamr@2:  * http://www.boost.org/LICENSE_1_0.txt)
williamr@2:  *
williamr@2:  * See http://www.boost.org for most recent version including documentation.
williamr@2:  *
williamr@2:  * $Id: geometric_distribution.hpp,v 1.16 2004/07/27 03:43:32 dgregor Exp $
williamr@2:  *
williamr@2:  * Revision history
williamr@2:  *  2001-02-18  moved to individual header files
williamr@2:  */
williamr@2: 
williamr@2: #ifndef BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
williamr@2: #define BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
williamr@2: 
williamr@2: #include <cmath>          // std::log
williamr@2: #include <cassert>
williamr@2: #include <iostream>
williamr@2: #include <boost/random/uniform_01.hpp>
williamr@2: 
williamr@2: namespace boost {
williamr@2: 
williamr@2: #if defined(__GNUC__) && (__GNUC__ < 3)
williamr@2: // Special gcc workaround: gcc 2.95.x ignores using-declarations
williamr@2: // in template classes (confirmed by gcc author Martin v. Loewis)
williamr@2:   using std::log;
williamr@2: #endif
williamr@2: 
williamr@2: // geometric distribution: p(i) = (1-p) * pow(p, i-1)   (integer)
williamr@2: template<class IntType = int, class RealType = double>
williamr@2: class geometric_distribution
williamr@2: {
williamr@2: public:
williamr@2:   typedef RealType input_type;
williamr@2:   typedef IntType result_type;
williamr@2: 
williamr@2:   explicit geometric_distribution(const RealType& p = RealType(0.5))
williamr@2:     : _p(p)
williamr@2:   {
williamr@2:     assert(RealType(0) < p && p < RealType(1));
williamr@2:     init();
williamr@2:   }
williamr@2: 
williamr@2:   // compiler-generated copy ctor and assignment operator are fine
williamr@2: 
williamr@2:   RealType p() const { return _p; }
williamr@2:   void reset() { }
williamr@2: 
williamr@2:   template<class Engine>
williamr@2:   result_type operator()(Engine& eng)
williamr@2:   {
williamr@2: #ifndef BOOST_NO_STDC_NAMESPACE
williamr@2:     using std::log;
williamr@2:     using std::floor;
williamr@2: #endif
williamr@2:     return IntType(floor(log(RealType(1)-eng()) / _log_p)) + IntType(1);
williamr@2:   }
williamr@2: 
williamr@2: #if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)
williamr@2:   template<class CharT, class Traits>
williamr@2:   friend std::basic_ostream<CharT,Traits>&
williamr@2:   operator<<(std::basic_ostream<CharT,Traits>& os, const geometric_distribution& gd)
williamr@2:   {
williamr@2:     os << gd._p;
williamr@2:     return os;
williamr@2:   }
williamr@2: 
williamr@2:   template<class CharT, class Traits>
williamr@2:   friend std::basic_istream<CharT,Traits>&
williamr@2:   operator>>(std::basic_istream<CharT,Traits>& is, geometric_distribution& gd)
williamr@2:   {
williamr@2:     is >> std::ws >> gd._p;
williamr@2:     gd.init();
williamr@2:     return is;
williamr@2:   }
williamr@2: #endif
williamr@2: 
williamr@2: private:
williamr@2:   void init()
williamr@2:   {
williamr@2: #ifndef BOOST_NO_STDC_NAMESPACE
williamr@2:     using std::log;
williamr@2: #endif
williamr@2:     _log_p = log(_p);
williamr@2:   }
williamr@2: 
williamr@2:   RealType _p;
williamr@2:   RealType _log_p;
williamr@2: };
williamr@2: 
williamr@2: } // namespace boost
williamr@2: 
williamr@2: #endif // BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
williamr@2: