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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
29template <class _RealType = double>
30class exponential_distribution {
31 static_assert(__libcpp_random_is_valid_realtype<_RealType>::value,
32 "RealType must be a supported floating-point type");
33
34public:
35 // types
36 typedef _RealType result_type;
37
38 class param_type {
39 result_type __lambda_;
40
41 public:
42 typedef exponential_distribution distribution_type;
43
44 _LIBCPP_HIDE_FROM_ABI explicit param_type(result_type __lambda = 1) : __lambda_(__lambda) {}
45
46 _LIBCPP_HIDE_FROM_ABI result_type lambda() const { return __lambda_; }
47
48 friend _LIBCPP_HIDE_FROM_ABI bool operator==(const param_type& __x, const param_type& __y) {
49 return __x.__lambda_ == __y.__lambda_;
50 }
51 friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const param_type& __x, const param_type& __y) { return !(__x == __y); }
52 };
53
54private:
55 param_type __p_;
56
57public:
58 // constructors and reset functions
59#ifndef _LIBCPP_CXX03_LANG
60 _LIBCPP_HIDE_FROM_ABI exponential_distribution() : exponential_distribution(1) {}
61 _LIBCPP_HIDE_FROM_ABI explicit exponential_distribution(result_type __lambda) : __p_(param_type(__lambda)) {}
62#else
63 _LIBCPP_HIDE_FROM_ABI explicit exponential_distribution(result_type __lambda = 1) : __p_(param_type(__lambda)) {}
64#endif
65 _LIBCPP_HIDE_FROM_ABI explicit exponential_distribution(const param_type& __p) : __p_(__p) {}
66 _LIBCPP_HIDE_FROM_ABI void reset() {}
67
68 // generating functions
69 template <class _URNG>
70 _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g) {
71 return (*this)(__g, __p_);
72 }
73 template <class _URNG>
74 _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
75
76 // property functions
77 _LIBCPP_HIDE_FROM_ABI result_type lambda() const { return __p_.lambda(); }
78
79 _LIBCPP_HIDE_FROM_ABI param_type param() const { return __p_; }
80 _LIBCPP_HIDE_FROM_ABI void param(const param_type& __p) { __p_ = __p; }
81
82 _LIBCPP_HIDE_FROM_ABI result_type min() const { return 0; }
83 _LIBCPP_HIDE_FROM_ABI result_type max() const { return numeric_limits<result_type>::infinity(); }
84
85 friend _LIBCPP_HIDE_FROM_ABI bool
86 operator==(const exponential_distribution& __x, const exponential_distribution& __y) {
87 return __x.__p_ == __y.__p_;
88 }
89 friend _LIBCPP_HIDE_FROM_ABI bool
90 operator!=(const exponential_distribution& __x, const exponential_distribution& __y) {
91 return !(__x == __y);
92 }
93};
94
95template <class _RealType>
96template <class _URNG>
97_RealType exponential_distribution<_RealType>::operator()(_URNG& __g, const param_type& __p) {
98 static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
99 return -std::log(result_type(1) - std::generate_canonical<result_type, numeric_limits<result_type>::digits>(__g)) /
100 __p.lambda();
101}
102
103template <class _CharT, class _Traits, class _RealType>
104_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
105operator<<(basic_ostream<_CharT, _Traits>& __os, const exponential_distribution<_RealType>& __x) {
106 __save_flags<_CharT, _Traits> __lx(__os);
107 typedef basic_ostream<_CharT, _Traits> _OStream;
108 __os.flags(_OStream::dec | _OStream::left | _OStream::fixed | _OStream::scientific);
109 return __os << __x.lambda();
110}
111
112template <class _CharT, class _Traits, class _RealType>
113_LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
114operator>>(basic_istream<_CharT, _Traits>& __is, exponential_distribution<_RealType>& __x) {
115 typedef exponential_distribution<_RealType> _Eng;
116 typedef typename _Eng::result_type result_type;
117 typedef typename _Eng::param_type param_type;
118 __save_flags<_CharT, _Traits> __lx(__is);
119 typedef basic_istream<_CharT, _Traits> _Istream;
120 __is.flags(_Istream::dec | _Istream::skipws);
121 result_type __lambda;
122 __is >> __lambda;
123 if (!__is.fail())
124 __x.param(param_type(__lambda));
125 return __is;
126}
127
128_LIBCPP_END_NAMESPACE_STD
129
130_LIBCPP_POP_MACROS
131
132#endif // _LIBCPP___RANDOM_EXPONENTIAL_DISTRIBUTION_H