boost/random/geometric_distribution.hpp
/* boost random/geometric_distribution.hpp header file
*
* Copyright Jens Maurer 2000-2001
* Permission to use, copy, modify, sell, and distribute this software
* is hereby granted without fee provided that the above copyright notice
* appears in all copies and that both that copyright notice and this
* permission notice appear in supporting documentation,
*
* Jens Maurer makes no representations about the suitability of this
* software for any purpose. It is provided "as is" without express or
* implied warranty.
*
* See http://www.boost.org for most recent version including documentation.
*
* $Id: geometric_distribution.hpp,v 1.14.2.1 2004/01/25 21:26:45 jmaurer 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