source: NonGTP/Boost/boost/random/geometric_distribution.hpp @ 857

Revision 857, 2.4 KB checked in by igarcia, 19 years ago (diff)
RevLine 
[857]1/* boost random/geometric_distribution.hpp header file
2 *
3 * Copyright Jens Maurer 2000-2001
4 * Distributed under the Boost Software License, Version 1.0. (See
5 * accompanying file LICENSE_1_0.txt or copy at
6 * http://www.boost.org/LICENSE_1_0.txt)
7 *
8 * See http://www.boost.org for most recent version including documentation.
9 *
10 * $Id: geometric_distribution.hpp,v 1.16 2004/07/27 03:43:32 dgregor Exp $
11 *
12 * Revision history
13 *  2001-02-18  moved to individual header files
14 */
15
16#ifndef BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
17#define BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
18
19#include <cmath>          // std::log
20#include <cassert>
21#include <iostream>
22#include <boost/random/uniform_01.hpp>
23
24namespace boost {
25
26#if defined(__GNUC__) && (__GNUC__ < 3)
27// Special gcc workaround: gcc 2.95.x ignores using-declarations
28// in template classes (confirmed by gcc author Martin v. Loewis)
29  using std::log;
30#endif
31
32// geometric distribution: p(i) = (1-p) * pow(p, i-1)   (integer)
33template<class IntType = int, class RealType = double>
34class geometric_distribution
35{
36public:
37  typedef RealType input_type;
38  typedef IntType result_type;
39
40  explicit geometric_distribution(const RealType& p = RealType(0.5))
41    : _p(p)
42  {
43    assert(RealType(0) < p && p < RealType(1));
44    init();
45  }
46
47  // compiler-generated copy ctor and assignment operator are fine
48
49  RealType p() const { return _p; }
50  void reset() { }
51
52  template<class Engine>
53  result_type operator()(Engine& eng)
54  {
55#ifndef BOOST_NO_STDC_NAMESPACE
56    using std::log;
57    using std::floor;
58#endif
59    return IntType(floor(log(RealType(1)-eng()) / _log_p)) + IntType(1);
60  }
61
62#if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)
63  template<class CharT, class Traits>
64  friend std::basic_ostream<CharT,Traits>&
65  operator<<(std::basic_ostream<CharT,Traits>& os, const geometric_distribution& gd)
66  {
67    os << gd._p;
68    return os;
69  }
70
71  template<class CharT, class Traits>
72  friend std::basic_istream<CharT,Traits>&
73  operator>>(std::basic_istream<CharT,Traits>& is, geometric_distribution& gd)
74  {
75    is >> std::ws >> gd._p;
76    gd.init();
77    return is;
78  }
79#endif
80
81private:
82  void init()
83  {
84#ifndef BOOST_NO_STDC_NAMESPACE
85    using std::log;
86#endif
87    _log_p = log(_p);
88  }
89
90  RealType _p;
91  RealType _log_p;
92};
93
94} // namespace boost
95
96#endif // BOOST_RANDOM_GEOMETRIC_DISTRIBUTION_HPP
97
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