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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_BINOMIAL_DISTRIBUTION_H
10#define _LIBCPP___RANDOM_BINOMIAL_DISTRIBUTION_H
11
12#include <__config>
13#include <__random/is_valid.h>
14#include <__random/uniform_real_distribution.h>
15#include <cmath>
16#include <iosfwd>
17
18#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
19# pragma GCC system_header
20#endif
21
22_LIBCPP_PUSH_MACROS
23#include <__undef_macros>
24
25_LIBCPP_BEGIN_NAMESPACE_STD
26
27template <class _IntType = int>
28class binomial_distribution {
29 static_assert(__libcpp_random_is_valid_inttype<_IntType>::value, "IntType must be a supported integer type");
30
31public:
32 // types
33 typedef _IntType result_type;
34
35 class param_type {
36 result_type __t_;
37 double __p_;
38 double __pr_;
39 double __odds_ratio_;
40 result_type __r0_;
41
42 public:
43 typedef binomial_distribution distribution_type;
44
45 _LIBCPP_HIDE_FROM_ABI explicit param_type(result_type __t = 1, double __p = 0.5);
46
47 _LIBCPP_HIDE_FROM_ABI result_type t() const { return __t_; }
48 _LIBCPP_HIDE_FROM_ABI double p() const { return __p_; }
49
50 friend _LIBCPP_HIDE_FROM_ABI bool operator==(const param_type& __x, const param_type& __y) {
51 return __x.__t_ == __y.__t_ && __x.__p_ == __y.__p_;
52 }
53 friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const param_type& __x, const param_type& __y) { return !(__x == __y); }
54
55 friend class binomial_distribution;
56 };
57
58private:
59 param_type __p_;
60
61public:
62 // constructors and reset functions
63#ifndef _LIBCPP_CXX03_LANG
64 _LIBCPP_HIDE_FROM_ABI binomial_distribution() : binomial_distribution(1) {}
65 _LIBCPP_HIDE_FROM_ABI explicit binomial_distribution(result_type __t, double __p = 0.5)
66 : __p_(param_type(__t, __p)) {}
67#else
68 _LIBCPP_HIDE_FROM_ABI explicit binomial_distribution(result_type __t = 1, double __p = 0.5)
69 : __p_(param_type(__t, __p)) {}
70#endif
71 _LIBCPP_HIDE_FROM_ABI explicit binomial_distribution(const param_type& __p) : __p_(__p) {}
72 _LIBCPP_HIDE_FROM_ABI void reset() {}
73
74 // generating functions
75 template <class _URNG>
76 _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g) {
77 return (*this)(__g, __p_);
78 }
79 template <class _URNG>
80 _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
81
82 // property functions
83 _LIBCPP_HIDE_FROM_ABI result_type t() const { return __p_.t(); }
84 _LIBCPP_HIDE_FROM_ABI double p() const { return __p_.p(); }
85
86 _LIBCPP_HIDE_FROM_ABI param_type param() const { return __p_; }
87 _LIBCPP_HIDE_FROM_ABI void param(const param_type& __p) { __p_ = __p; }
88
89 _LIBCPP_HIDE_FROM_ABI result_type min() const { return 0; }
90 _LIBCPP_HIDE_FROM_ABI result_type max() const { return t(); }
91
92 friend _LIBCPP_HIDE_FROM_ABI bool operator==(const binomial_distribution& __x, const binomial_distribution& __y) {
93 return __x.__p_ == __y.__p_;
94 }
95 friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const binomial_distribution& __x, const binomial_distribution& __y) {
96 return !(__x == __y);
97 }
98};
99
100// The LLVM C library provides this with conflicting `noexcept` attributes.
101#if !defined(_LIBCPP_MSVCRT_LIKE) && !defined(__LLVM_LIBC__)
102extern "C" double lgamma_r(double, int*);
103#endif
104
105inline _LIBCPP_HIDE_FROM_ABI double __libcpp_lgamma(double __d) {
106#if defined(_LIBCPP_MSVCRT_LIKE) || defined(__LLVM_LIBC__)
107 return lgamma(__d);
108#else
109 int __sign;
110 return lgamma_r(__d, &__sign);
111#endif
112}
113
114template <class _IntType>
115binomial_distribution<_IntType>::param_type::param_type(result_type __t, double __p) : __t_(__t), __p_(__p) {
116 if (0 < __p_ && __p_ < 1) {
117 __r0_ = static_cast<result_type>((__t_ + 1) * __p_);
118 __pr_ = std::exp(
119 std::__libcpp_lgamma(__t_ + 1.) - std::__libcpp_lgamma(__r0_ + 1.) - std::__libcpp_lgamma(__t_ - __r0_ + 1.) +
120 __r0_ * std::log(__p_) + (__t_ - __r0_) * std::log(1 - __p_));
121 __odds_ratio_ = __p_ / (1 - __p_);
122 }
123}
124
125// Reference: Kemp, C.D. (1986). `A modal method for generating binomial
126// variables', Commun. Statist. - Theor. Meth. 15(3), 805-813.
127template <class _IntType>
128template <class _URNG>
129_IntType binomial_distribution<_IntType>::operator()(_URNG& __g, const param_type& __pr) {
130 static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
131 if (__pr.__t_ == 0 || __pr.__p_ == 0)
132 return 0;
133 if (__pr.__p_ == 1)
134 return __pr.__t_;
135 uniform_real_distribution<double> __gen;
136 double __u = __gen(__g) - __pr.__pr_;
137 if (__u < 0)
138 return __pr.__r0_;
139 double __pu = __pr.__pr_;
140 double __pd = __pu;
141 result_type __ru = __pr.__r0_;
142 result_type __rd = __ru;
143 while (true) {
144 bool __break = true;
145 if (__rd >= 1) {
146 __pd *= __rd / (__pr.__odds_ratio_ * (__pr.__t_ - __rd + 1));
147 __u -= __pd;
148 __break = false;
149 if (__u < 0)
150 return __rd - 1;
151 }
152 if (__rd != 0)
153 --__rd;
154 ++__ru;
155 if (__ru <= __pr.__t_) {
156 __pu *= (__pr.__t_ - __ru + 1) * __pr.__odds_ratio_ / __ru;
157 __u -= __pu;
158 __break = false;
159 if (__u < 0)
160 return __ru;
161 }
162 if (__break)
163 return 0;
164 }
165}
166
167template <class _CharT, class _Traits, class _IntType>
168_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
169operator<<(basic_ostream<_CharT, _Traits>& __os, const binomial_distribution<_IntType>& __x) {
170 __save_flags<_CharT, _Traits> __lx(__os);
171 typedef basic_ostream<_CharT, _Traits> _OStream;
172 __os.flags(_OStream::dec | _OStream::left | _OStream::fixed | _OStream::scientific);
173 _CharT __sp = __os.widen(' ');
174 __os.fill(__sp);
175 return __os << __x.t() << __sp << __x.p();
176}
177
178template <class _CharT, class _Traits, class _IntType>
179_LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
180operator>>(basic_istream<_CharT, _Traits>& __is, binomial_distribution<_IntType>& __x) {
181 typedef binomial_distribution<_IntType> _Eng;
182 typedef typename _Eng::result_type result_type;
183 typedef typename _Eng::param_type param_type;
184 __save_flags<_CharT, _Traits> __lx(__is);
185 typedef basic_istream<_CharT, _Traits> _Istream;
186 __is.flags(_Istream::dec | _Istream::skipws);
187 result_type __t;
188 double __p;
189 __is >> __t >> __p;
190 if (!__is.fail())
191 __x.param(param_type(__t, __p));
192 return __is;
193}
194
195_LIBCPP_END_NAMESPACE_STD
196
197_LIBCPP_POP_MACROS
198
199#endif // _LIBCPP___RANDOM_BINOMIAL_DISTRIBUTION_H