1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef _LIBCPP___RANDOM_EXPONENTIAL_DISTRIBUTION_H
10 #define _LIBCPP___RANDOM_EXPONENTIAL_DISTRIBUTION_H
11 
12 #include <__config>
13 #include <__random/generate_canonical.h>
14 #include <__random/is_valid.h>
15 #include <__random/uniform_real_distribution.h>
16 #include <cmath>
17 #include <iosfwd>
18 #include <limits>
19 
20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
21 #  pragma GCC system_header
22 #endif
23 
24 _LIBCPP_PUSH_MACROS
25 #include <__undef_macros>
26 
27 _LIBCPP_BEGIN_NAMESPACE_STD
28 
29 template<class _RealType = double>
30 class _LIBCPP_TEMPLATE_VIS exponential_distribution
31 {
32 public:
33     // types
34     typedef _RealType result_type;
35 
36     class _LIBCPP_TEMPLATE_VIS param_type
37     {
38         result_type __lambda_;
39     public:
40         typedef exponential_distribution distribution_type;
41 
42         _LIBCPP_INLINE_VISIBILITY
43         explicit param_type(result_type __lambda = 1) : __lambda_(__lambda) {}
44 
45         _LIBCPP_INLINE_VISIBILITY
46         result_type lambda() const {return __lambda_;}
47 
48         friend _LIBCPP_INLINE_VISIBILITY
49             bool operator==(const param_type& __x, const param_type& __y)
50             {return __x.__lambda_ == __y.__lambda_;}
51         friend _LIBCPP_INLINE_VISIBILITY
52             bool operator!=(const param_type& __x, const param_type& __y)
53             {return !(__x == __y);}
54     };
55 
56 private:
57     param_type __p_;
58 
59 public:
60     // constructors and reset functions
61 #ifndef _LIBCPP_CXX03_LANG
62     _LIBCPP_INLINE_VISIBILITY
63     exponential_distribution() : exponential_distribution(1) {}
64     _LIBCPP_INLINE_VISIBILITY
65     explicit exponential_distribution(result_type __lambda)
66         : __p_(param_type(__lambda)) {}
67 #else
68     _LIBCPP_INLINE_VISIBILITY
69     explicit exponential_distribution(result_type __lambda = 1)
70         : __p_(param_type(__lambda)) {}
71 #endif
72     _LIBCPP_INLINE_VISIBILITY
73     explicit exponential_distribution(const param_type& __p) : __p_(__p) {}
74     _LIBCPP_INLINE_VISIBILITY
75     void reset() {}
76 
77     // generating functions
78     template<class _URNG>
79         _LIBCPP_INLINE_VISIBILITY
80         result_type operator()(_URNG& __g)
81         {return (*this)(__g, __p_);}
82     template<class _URNG>
83     _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
84 
85     // property functions
86     _LIBCPP_INLINE_VISIBILITY
87     result_type lambda() const {return __p_.lambda();}
88 
89     _LIBCPP_INLINE_VISIBILITY
90     param_type param() const {return __p_;}
91     _LIBCPP_INLINE_VISIBILITY
92     void param(const param_type& __p) {__p_ = __p;}
93 
94     _LIBCPP_INLINE_VISIBILITY
95     result_type min() const {return 0;}
96     _LIBCPP_INLINE_VISIBILITY
97     result_type max() const {return numeric_limits<result_type>::infinity();}
98 
99     friend _LIBCPP_INLINE_VISIBILITY
100         bool operator==(const exponential_distribution& __x,
101                         const exponential_distribution& __y)
102         {return __x.__p_ == __y.__p_;}
103     friend _LIBCPP_INLINE_VISIBILITY
104         bool operator!=(const exponential_distribution& __x,
105                         const exponential_distribution& __y)
106         {return !(__x == __y);}
107 };
108 
109 template <class _RealType>
110 template<class _URNG>
111 _RealType
112 exponential_distribution<_RealType>::operator()(_URNG& __g, const param_type& __p)
113 {
114     static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
115     return -_VSTD::log
116                   (
117                       result_type(1) -
118                       _VSTD::generate_canonical<result_type,
119                                        numeric_limits<result_type>::digits>(__g)
120                   )
121                   / __p.lambda();
122 }
123 
124 template <class _CharT, class _Traits, class _RealType>
125 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
126 operator<<(basic_ostream<_CharT, _Traits>& __os,
127            const exponential_distribution<_RealType>& __x)
128 {
129     __save_flags<_CharT, _Traits> __lx(__os);
130     typedef basic_ostream<_CharT, _Traits> _OStream;
131     __os.flags(_OStream::dec | _OStream::left | _OStream::fixed |
132                _OStream::scientific);
133     return __os << __x.lambda();
134 }
135 
136 template <class _CharT, class _Traits, class _RealType>
137 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
138 operator>>(basic_istream<_CharT, _Traits>& __is,
139            exponential_distribution<_RealType>& __x)
140 {
141     typedef exponential_distribution<_RealType> _Eng;
142     typedef typename _Eng::result_type result_type;
143     typedef typename _Eng::param_type param_type;
144     __save_flags<_CharT, _Traits> __lx(__is);
145     typedef basic_istream<_CharT, _Traits> _Istream;
146     __is.flags(_Istream::dec | _Istream::skipws);
147     result_type __lambda;
148     __is >> __lambda;
149     if (!__is.fail())
150         __x.param(param_type(__lambda));
151     return __is;
152 }
153 
154 _LIBCPP_END_NAMESPACE_STD
155 
156 _LIBCPP_POP_MACROS
157 
158 #endif // _LIBCPP___RANDOM_EXPONENTIAL_DISTRIBUTION_H
159