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         explicit param_type(result_type __t = 1, double __p = 0.5);
46 
47         _LIBCPP_INLINE_VISIBILITY
48         result_type t() const {return __t_;}
49         _LIBCPP_INLINE_VISIBILITY
50         double p() const {return __p_;}
51 
52         friend _LIBCPP_INLINE_VISIBILITY
53             bool operator==(const param_type& __x, const param_type& __y)
54             {return __x.__t_ == __y.__t_ && __x.__p_ == __y.__p_;}
55         friend _LIBCPP_INLINE_VISIBILITY
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_INLINE_VISIBILITY
69     binomial_distribution() : binomial_distribution(1) {}
70     _LIBCPP_INLINE_VISIBILITY
71     explicit binomial_distribution(result_type __t, double __p = 0.5)
72         : __p_(param_type(__t, __p)) {}
73 #else
74     _LIBCPP_INLINE_VISIBILITY
75     explicit binomial_distribution(result_type __t = 1, double __p = 0.5)
76         : __p_(param_type(__t, __p)) {}
77 #endif
78     _LIBCPP_INLINE_VISIBILITY
79     explicit binomial_distribution(const param_type& __p) : __p_(__p) {}
80     _LIBCPP_INLINE_VISIBILITY
81     void reset() {}
82 
83     // generating functions
84     template<class _URNG>
85         _LIBCPP_INLINE_VISIBILITY
86         result_type operator()(_URNG& __g)
87         {return (*this)(__g, __p_);}
88     template<class _URNG> result_type operator()(_URNG& __g, const param_type& __p);
89 
90     // property functions
91     _LIBCPP_INLINE_VISIBILITY
92     result_type t() const {return __p_.t();}
93     _LIBCPP_INLINE_VISIBILITY
94     double p() const {return __p_.p();}
95 
96     _LIBCPP_INLINE_VISIBILITY
97     param_type param() const {return __p_;}
98     _LIBCPP_INLINE_VISIBILITY
99     void param(const param_type& __p) {__p_ = __p;}
100 
101     _LIBCPP_INLINE_VISIBILITY
102     result_type min() const {return 0;}
103     _LIBCPP_INLINE_VISIBILITY
104     result_type max() const {return t();}
105 
106     friend _LIBCPP_INLINE_VISIBILITY
107         bool operator==(const binomial_distribution& __x,
108                         const binomial_distribution& __y)
109         {return __x.__p_ == __y.__p_;}
110     friend _LIBCPP_INLINE_VISIBILITY
111         bool operator!=(const binomial_distribution& __x,
112                         const binomial_distribution& __y)
113         {return !(__x == __y);}
114 };
115 
116 #ifndef _LIBCPP_MSVCRT_LIKE
117 extern "C" double lgamma_r(double, int *);
118 #endif
119 
120 inline _LIBCPP_INLINE_VISIBILITY double __libcpp_lgamma(double __d) {
121 #if defined(_LIBCPP_MSVCRT_LIKE)
122   return lgamma(__d);
123 #else
124   int __sign;
125   return lgamma_r(__d, &__sign);
126 #endif
127 }
128 
129 template<class _IntType>
130 binomial_distribution<_IntType>::param_type::param_type(result_type __t, double __p)
131     : __t_(__t), __p_(__p)
132 {
133     if (0 < __p_ && __p_ < 1)
134     {
135         __r0_ = static_cast<result_type>((__t_ + 1) * __p_);
136         __pr_ = _VSTD::exp(std::__libcpp_lgamma(__t_ + 1.) -
137                            std::__libcpp_lgamma(__r0_ + 1.) -
138                            std::__libcpp_lgamma(__t_ - __r0_ + 1.) + __r0_ * _VSTD::log(__p_) +
139                            (__t_ - __r0_) * _VSTD::log(1 - __p_));
140         __odds_ratio_ = __p_ / (1 - __p_);
141     }
142 }
143 
144 // Reference: Kemp, C.D. (1986). `A modal method for generating binomial
145 //           variables', Commun. Statist. - Theor. Meth. 15(3), 805-813.
146 template<class _IntType>
147 template<class _URNG>
148 _IntType
149 binomial_distribution<_IntType>::operator()(_URNG& __g, const param_type& __pr)
150 {
151     static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
152     if (__pr.__t_ == 0 || __pr.__p_ == 0)
153         return 0;
154     if (__pr.__p_ == 1)
155         return __pr.__t_;
156     uniform_real_distribution<double> __gen;
157     double __u = __gen(__g) - __pr.__pr_;
158     if (__u < 0)
159         return __pr.__r0_;
160     double __pu = __pr.__pr_;
161     double __pd = __pu;
162     result_type __ru = __pr.__r0_;
163     result_type __rd = __ru;
164     while (true)
165     {
166         bool __break = true;
167         if (__rd >= 1)
168         {
169             __pd *= __rd / (__pr.__odds_ratio_ * (__pr.__t_ - __rd + 1));
170             __u -= __pd;
171             __break = false;
172             if (__u < 0)
173                 return __rd - 1;
174         }
175         if ( __rd != 0 )
176             --__rd;
177         ++__ru;
178         if (__ru <= __pr.__t_)
179         {
180             __pu *= (__pr.__t_ - __ru + 1) * __pr.__odds_ratio_ / __ru;
181             __u -= __pu;
182             __break = false;
183             if (__u < 0)
184                 return __ru;
185         }
186         if (__break)
187             return 0;
188     }
189 }
190 
191 template <class _CharT, class _Traits, class _IntType>
192 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
193 operator<<(basic_ostream<_CharT, _Traits>& __os,
194            const binomial_distribution<_IntType>& __x)
195 {
196     __save_flags<_CharT, _Traits> __lx(__os);
197     typedef basic_ostream<_CharT, _Traits> _OStream;
198     __os.flags(_OStream::dec | _OStream::left | _OStream::fixed |
199                _OStream::scientific);
200     _CharT __sp = __os.widen(' ');
201     __os.fill(__sp);
202     return __os << __x.t() << __sp << __x.p();
203 }
204 
205 template <class _CharT, class _Traits, class _IntType>
206 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
207 operator>>(basic_istream<_CharT, _Traits>& __is,
208            binomial_distribution<_IntType>& __x)
209 {
210     typedef binomial_distribution<_IntType> _Eng;
211     typedef typename _Eng::result_type result_type;
212     typedef typename _Eng::param_type param_type;
213     __save_flags<_CharT, _Traits> __lx(__is);
214     typedef basic_istream<_CharT, _Traits> _Istream;
215     __is.flags(_Istream::dec | _Istream::skipws);
216     result_type __t;
217     double __p;
218     __is >> __t >> __p;
219     if (!__is.fail())
220         __x.param(param_type(__t, __p));
221     return __is;
222 }
223 
224 _LIBCPP_END_NAMESPACE_STD
225 
226 _LIBCPP_POP_MACROS
227 
228 #endif // _LIBCPP___RANDOM_BINOMIAL_DISTRIBUTION_H
229