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