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 
27 template<class _IntType = int>
28 class _LIBCPP_TEMPLATE_VIS binomial_distribution
29 {
30     static_assert(__libcpp_random_is_valid_inttype<_IntType>::value, "IntType must be a supported integer type");
31 public:
32     // types
33     typedef _IntType result_type;
34 
35     class _LIBCPP_TEMPLATE_VIS param_type
36     {
37         result_type __t_;
38         double __p_;
39         double __pr_;
40         double __odds_ratio_;
41         result_type __r0_;
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
48         result_type t() const {return __t_;}
49         _LIBCPP_HIDE_FROM_ABI
50         double p() const {return __p_;}
51 
52         friend _LIBCPP_HIDE_FROM_ABI
53             bool operator==(const param_type& __x, const param_type& __y)
54             {return __x.__t_ == __y.__t_ && __x.__p_ == __y.__p_;}
55         friend _LIBCPP_HIDE_FROM_ABI
56             bool operator!=(const param_type& __x, const param_type& __y)
57             {return !(__x == __y);}
58 
59         friend class binomial_distribution;
60     };
61 
62 private:
63     param_type __p_;
64 
65 public:
66     // constructors and reset functions
67 #ifndef _LIBCPP_CXX03_LANG
68     _LIBCPP_HIDE_FROM_ABI
69     binomial_distribution() : binomial_distribution(1) {}
70     _LIBCPP_HIDE_FROM_ABI
71     explicit binomial_distribution(result_type __t, double __p = 0.5)
72         : __p_(param_type(__t, __p)) {}
73 #else
74     _LIBCPP_HIDE_FROM_ABI
75     explicit binomial_distribution(result_type __t = 1, double __p = 0.5)
76         : __p_(param_type(__t, __p)) {}
77 #endif
78     _LIBCPP_HIDE_FROM_ABI
79     explicit binomial_distribution(const param_type& __p) : __p_(__p) {}
80     _LIBCPP_HIDE_FROM_ABI
81     void reset() {}
82 
83     // generating functions
84     template<class _URNG>
85         _LIBCPP_HIDE_FROM_ABI
86         result_type operator()(_URNG& __g)
87         {return (*this)(__g, __p_);}
88     template<class _URNG>
89     _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
90 
91     // property functions
92     _LIBCPP_HIDE_FROM_ABI
93     result_type t() const {return __p_.t();}
94     _LIBCPP_HIDE_FROM_ABI
95     double p() const {return __p_.p();}
96 
97     _LIBCPP_HIDE_FROM_ABI
98     param_type param() const {return __p_;}
99     _LIBCPP_HIDE_FROM_ABI
100     void param(const param_type& __p) {__p_ = __p;}
101 
102     _LIBCPP_HIDE_FROM_ABI
103     result_type min() const {return 0;}
104     _LIBCPP_HIDE_FROM_ABI
105     result_type max() const {return t();}
106 
107     friend _LIBCPP_HIDE_FROM_ABI
108         bool operator==(const binomial_distribution& __x,
109                         const binomial_distribution& __y)
110         {return __x.__p_ == __y.__p_;}
111     friend _LIBCPP_HIDE_FROM_ABI
112         bool operator!=(const binomial_distribution& __x,
113                         const binomial_distribution& __y)
114         {return !(__x == __y);}
115 };
116 
117 #ifndef _LIBCPP_MSVCRT_LIKE
118 extern "C" double lgamma_r(double, int *);
119 #endif
120 
121 inline _LIBCPP_HIDE_FROM_ABI double __libcpp_lgamma(double __d) {
122 #if defined(_LIBCPP_MSVCRT_LIKE)
123   return lgamma(__d);
124 #else
125   int __sign;
126   return lgamma_r(__d, &__sign);
127 #endif
128 }
129 
130 template<class _IntType>
131 binomial_distribution<_IntType>::param_type::param_type(result_type __t, double __p)
132     : __t_(__t), __p_(__p)
133 {
134     if (0 < __p_ && __p_ < 1)
135     {
136         __r0_ = static_cast<result_type>((__t_ + 1) * __p_);
137         __pr_ = std::exp(std::__libcpp_lgamma(__t_ + 1.) -
138                            std::__libcpp_lgamma(__r0_ + 1.) -
139                            std::__libcpp_lgamma(__t_ - __r0_ + 1.) + __r0_ * std::log(__p_) +
140                            (__t_ - __r0_) * std::log(1 - __p_));
141         __odds_ratio_ = __p_ / (1 - __p_);
142     }
143 }
144 
145 // Reference: Kemp, C.D. (1986). `A modal method for generating binomial
146 //           variables', Commun. Statist. - Theor. Meth. 15(3), 805-813.
147 template<class _IntType>
148 template<class _URNG>
149 _IntType
150 binomial_distribution<_IntType>::operator()(_URNG& __g, const param_type& __pr)
151 {
152     static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
153     if (__pr.__t_ == 0 || __pr.__p_ == 0)
154         return 0;
155     if (__pr.__p_ == 1)
156         return __pr.__t_;
157     uniform_real_distribution<double> __gen;
158     double __u = __gen(__g) - __pr.__pr_;
159     if (__u < 0)
160         return __pr.__r0_;
161     double __pu = __pr.__pr_;
162     double __pd = __pu;
163     result_type __ru = __pr.__r0_;
164     result_type __rd = __ru;
165     while (true)
166     {
167         bool __break = true;
168         if (__rd >= 1)
169         {
170             __pd *= __rd / (__pr.__odds_ratio_ * (__pr.__t_ - __rd + 1));
171             __u -= __pd;
172             __break = false;
173             if (__u < 0)
174                 return __rd - 1;
175         }
176         if ( __rd != 0 )
177             --__rd;
178         ++__ru;
179         if (__ru <= __pr.__t_)
180         {
181             __pu *= (__pr.__t_ - __ru + 1) * __pr.__odds_ratio_ / __ru;
182             __u -= __pu;
183             __break = false;
184             if (__u < 0)
185                 return __ru;
186         }
187         if (__break)
188             return 0;
189     }
190 }
191 
192 template <class _CharT, class _Traits, class _IntType>
193 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
194 operator<<(basic_ostream<_CharT, _Traits>& __os,
195            const binomial_distribution<_IntType>& __x)
196 {
197     __save_flags<_CharT, _Traits> __lx(__os);
198     typedef basic_ostream<_CharT, _Traits> _OStream;
199     __os.flags(_OStream::dec | _OStream::left | _OStream::fixed |
200                _OStream::scientific);
201     _CharT __sp = __os.widen(' ');
202     __os.fill(__sp);
203     return __os << __x.t() << __sp << __x.p();
204 }
205 
206 template <class _CharT, class _Traits, class _IntType>
207 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
208 operator>>(basic_istream<_CharT, _Traits>& __is,
209            binomial_distribution<_IntType>& __x)
210 {
211     typedef binomial_distribution<_IntType> _Eng;
212     typedef typename _Eng::result_type result_type;
213     typedef typename _Eng::param_type param_type;
214     __save_flags<_CharT, _Traits> __lx(__is);
215     typedef basic_istream<_CharT, _Traits> _Istream;
216     __is.flags(_Istream::dec | _Istream::skipws);
217     result_type __t;
218     double __p;
219     __is >> __t >> __p;
220     if (!__is.fail())
221         __x.param(param_type(__t, __p));
222     return __is;
223 }
224 
225 _LIBCPP_END_NAMESPACE_STD
226 
227 _LIBCPP_POP_MACROS
228 
229 #endif // _LIBCPP___RANDOM_BINOMIAL_DISTRIBUTION_H
230