119 lines
2.9 KiB
C++
119 lines
2.9 KiB
C++
/* boost random/geometric_distribution.hpp header file
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*
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* Copyright Jens Maurer 2000-2001
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* Distributed under the Boost Software License, Version 1.0. (See
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* accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* See http://www.boost.org for most recent version including documentation.
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*
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* $Id: geometric_distribution.hpp 60755 2010-03-22 00:45:06Z steven_watanabe $
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*
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* Revision history
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* 2001-02-18 moved to individual header files
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*/
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#ifndef BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
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#define BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
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#include <boost/config/no_tr1/cmath.hpp> // std::log
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#include <cassert>
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#include <iostream>
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#include <boost/random/detail/config.hpp>
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#include <boost/random/uniform_01.hpp>
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namespace boost {
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#if defined(__GNUC__) && (__GNUC__ < 3)
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// Special gcc workaround: gcc 2.95.x ignores using-declarations
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// in template classes (confirmed by gcc author Martin v. Loewis)
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using std::log;
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#endif
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/**
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* An instantiation of the class template @c geometric_distribution models
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* a \random_distribution. The distribution produces positive
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* integers which are the number of bernoulli trials
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* with probability @c p required to get one that fails.
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*
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* For the geometric distribution, \f$p(i) = (1-p) p^{i-1}\f$.
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*/
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template<class IntType = int, class RealType = double>
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class geometric_distribution
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{
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public:
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typedef RealType input_type;
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typedef IntType result_type;
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/**
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* Contructs a new geometric_distribution with the paramter @c p.
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*
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* Requires: 0 < p < 1
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*/
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explicit geometric_distribution(const RealType& p = RealType(0.5))
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: _p(p)
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{
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assert(RealType(0) < _p && _p < RealType(1));
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init();
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}
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// compiler-generated copy ctor and assignment operator are fine
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/**
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* Returns: the distribution parameter @c p
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*/
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RealType p() const { return _p; }
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void reset() { }
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template<class Engine>
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result_type operator()(Engine& eng)
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{
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#ifndef BOOST_NO_STDC_NAMESPACE
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using std::log;
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using std::floor;
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#endif
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return IntType(floor(log(RealType(1)-eng()) / _log_p)) + IntType(1);
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}
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#ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
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template<class CharT, class Traits>
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friend std::basic_ostream<CharT,Traits>&
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operator<<(std::basic_ostream<CharT,Traits>& os, const geometric_distribution& gd)
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{
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os << gd._p;
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return os;
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}
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template<class CharT, class Traits>
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friend std::basic_istream<CharT,Traits>&
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operator>>(std::basic_istream<CharT,Traits>& is, geometric_distribution& gd)
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{
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is >> std::ws >> gd._p;
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gd.init();
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return is;
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}
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#endif
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private:
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/// \cond hide_private_functions
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void init()
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{
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#ifndef BOOST_NO_STDC_NAMESPACE
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using std::log;
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#endif
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_log_p = log(_p);
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}
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/// \endcond
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RealType _p;
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RealType _log_p;
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};
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} // namespace boost
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#endif // BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
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