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// Some libc declares the math functions to be `noexcept`.
101#if _LIBCPP_GLIBC_PREREQ(2, 8) || _LIBCPP_LIBC_LLVM_LIBC
102# define _LIBCPP_LGAMMA_R_NOEXCEPT _NOEXCEPT
103#else
104# define _LIBCPP_LGAMMA_R_NOEXCEPT
105#endif
106
107#if !defined(_LIBCPP_MSVCRT_LIKE)
108extern "C" double lgamma_r(double, int*) _LIBCPP_LGAMMA_R_NOEXCEPT;
109#endif
110
111inline _LIBCPP_HIDE_FROM_ABI double __libcpp_lgamma(double __d) {
112#if defined(_LIBCPP_MSVCRT_LIKE)
113 return lgamma(__d);
114#else
115 int __sign;
116 return lgamma_r(__d, &__sign);
117#endif
118}
119
120template <class _IntType>
121binomial_distribution<_IntType>::param_type::param_type(result_type __t, double __p) : __t_(__t), __p_(__p) {
122 if (0 < __p_ && __p_ < 1) {
123 __r0_ = static_cast<result_type>((__t_ + 1) * __p_);
124 __pr_ = std::exp(
125 std::__libcpp_lgamma(d: __t_ + 1.) - std::__libcpp_lgamma(d: __r0_ + 1.) - std::__libcpp_lgamma(d: __t_ - __r0_ + 1.) +
126 __r0_ * std::log(x: __p_) + (__t_ - __r0_) * std::log(x: 1 - __p_));
127 __odds_ratio_ = __p_ / (1 - __p_);
128 }
129}
130
131// Reference: Kemp, C.D. (1986). `A modal method for generating binomial
132// variables', Commun. Statist. - Theor. Meth. 15(3), 805-813.
133template <class _IntType>
134template <class _URNG>
135_IntType binomial_distribution<_IntType>::operator()(_URNG& __g, const param_type& __pr) {
136 static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
137 if (__pr.__t_ == 0 || __pr.__p_ == 0)
138 return 0;
139 if (__pr.__p_ == 1)
140 return __pr.__t_;
141 uniform_real_distribution<double> __gen;
142 double __u = __gen(__g) - __pr.__pr_;
143 if (__u < 0)
144 return __pr.__r0_;
145 double __pu = __pr.__pr_;
146 double __pd = __pu;
147 result_type __ru = __pr.__r0_;
148 result_type __rd = __ru;
149 while (true) {
150 bool __break = true;
151 if (__rd >= 1) {
152 __pd *= __rd / (__pr.__odds_ratio_ * (__pr.__t_ - __rd + 1));
153 __u -= __pd;
154 __break = false;
155 if (__u < 0)
156 return __rd - 1;
157 }
158 if (__rd != 0)
159 --__rd;
160 ++__ru;
161 if (__ru <= __pr.__t_) {
162 __pu *= (__pr.__t_ - __ru + 1) * __pr.__odds_ratio_ / __ru;
163 __u -= __pu;
164 __break = false;
165 if (__u < 0)
166 return __ru;
167 }
168 if (__break)
169 return 0;
170 }
171}
172
173template <class _CharT, class _Traits, class _IntType>
174_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
175operator<<(basic_ostream<_CharT, _Traits>& __os, const binomial_distribution<_IntType>& __x) {
176 __save_flags<_CharT, _Traits> __lx(__os);
177 typedef basic_ostream<_CharT, _Traits> _OStream;
178 __os.flags(_OStream::dec | _OStream::left | _OStream::fixed | _OStream::scientific);
179 _CharT __sp = __os.widen(' ');
180 __os.fill(__sp);
181 return __os << __x.t() << __sp << __x.p();
182}
183
184template <class _CharT, class _Traits, class _IntType>
185_LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
186operator>>(basic_istream<_CharT, _Traits>& __is, binomial_distribution<_IntType>& __x) {
187 typedef binomial_distribution<_IntType> _Eng;
188 typedef typename _Eng::result_type result_type;
189 typedef typename _Eng::param_type param_type;
190 __save_flags<_CharT, _Traits> __lx(__is);
191 typedef basic_istream<_CharT, _Traits> _Istream;
192 __is.flags(_Istream::dec | _Istream::skipws);
193 result_type __t;
194 double __p;
195 __is >> __t >> __p;
196 if (!__is.fail())
197 __x.param(param_type(__t, __p));
198 return __is;
199}
200
201_LIBCPP_END_NAMESPACE_STD
202
203_LIBCPP_POP_MACROS
204
205#endif // _LIBCPP___RANDOM_BINOMIAL_DISTRIBUTION_H
206