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_POISSON_DISTRIBUTION_H
10#define _LIBCPP___RANDOM_POISSON_DISTRIBUTION_H
11
12#include <__config>
13#include <__math/abs.h>
14#include <__math/exponential_functions.h>
15#include <__math/logarithms.h>
16#include <__math/roots.h>
17#include <__math/rounding_functions.h>
18#include <__math/traits.h>
19#include <__random/clamp_to_integral.h>
20#include <__random/exponential_distribution.h>
21#include <__random/is_valid.h>
22#include <__random/normal_distribution.h>
23#include <__random/uniform_real_distribution.h>
24#include <iosfwd>
25#include <limits>
26
27#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
28# pragma GCC system_header
29#endif
30
31_LIBCPP_PUSH_MACROS
32#include <__undef_macros>
33
34_LIBCPP_BEGIN_NAMESPACE_STD
35
36template <class _IntType = int>
37class poisson_distribution {
38 static_assert(__libcpp_random_is_valid_inttype<_IntType>::value, "IntType must be a supported integer type");
39
40public:
41 // types
42 typedef _IntType result_type;
43
44 class param_type {
45 double __mean_;
46 double __s_;
47 double __d_;
48 double __l_;
49 double __omega_;
50 double __c0_;
51 double __c1_;
52 double __c2_;
53 double __c3_;
54 double __c_;
55
56 public:
57 typedef poisson_distribution distribution_type;
58
59 _LIBCPP_HIDE_FROM_ABI explicit param_type(double __mean = 1.0);
60
61 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double mean() const { return __mean_; }
62
63 friend _LIBCPP_HIDE_FROM_ABI bool operator==(const param_type& __x, const param_type& __y) {
64 return __x.__mean_ == __y.__mean_;
65 }
66 friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const param_type& __x, const param_type& __y) { return !(__x == __y); }
67
68 friend class poisson_distribution;
69 };
70
71private:
72 param_type __p_;
73
74public:
75 // constructors and reset functions
76#ifndef _LIBCPP_CXX03_LANG
77 _LIBCPP_HIDE_FROM_ABI poisson_distribution() : poisson_distribution(1.0) {}
78 _LIBCPP_HIDE_FROM_ABI explicit poisson_distribution(double __mean) : __p_(__mean) {}
79#else
80 _LIBCPP_HIDE_FROM_ABI explicit poisson_distribution(double __mean = 1.0) : __p_(__mean) {}
81#endif
82 _LIBCPP_HIDE_FROM_ABI explicit poisson_distribution(const param_type& __p) : __p_(__p) {}
83 _LIBCPP_HIDE_FROM_ABI void reset() {}
84
85 // generating functions
86 template <class _URNG>
87 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g) {
88 return (*this)(__g, __p_);
89 }
90 template <class _URNG>
91 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
92
93 // property functions
94 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI double mean() const { return __p_.mean(); }
95
96 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI param_type param() const { return __p_; }
97 _LIBCPP_HIDE_FROM_ABI void param(const param_type& __p) { __p_ = __p; }
98
99 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI result_type min() const { return 0; }
100 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI result_type max() const { return numeric_limits<result_type>::max(); }
101
102 friend _LIBCPP_HIDE_FROM_ABI bool operator==(const poisson_distribution& __x, const poisson_distribution& __y) {
103 return __x.__p_ == __y.__p_;
104 }
105 friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const poisson_distribution& __x, const poisson_distribution& __y) {
106 return !(__x == __y);
107 }
108};
109
110template <class _IntType>
111poisson_distribution<_IntType>::param_type::param_type(double __mean)
112 // According to the standard `inf` is a valid input, but it causes the
113 // distribution to hang, so we replace it with the maximum representable
114 // mean.
115 : __mean_(__math::isinf(x: __mean) ? numeric_limits<double>::max() : __mean) {
116 if (__mean_ < 10) {
117 __s_ = 0;
118 __d_ = 0;
119 __l_ = __math::exp(x: -__mean_);
120 __omega_ = 0;
121 __c3_ = 0;
122 __c2_ = 0;
123 __c1_ = 0;
124 __c0_ = 0;
125 __c_ = 0;
126 } else {
127 __s_ = __math::sqrt(x: __mean_);
128 __d_ = 6 * __mean_ * __mean_;
129 __l_ = __math::trunc(x: __mean_ - 1.1484);
130 __omega_ = .3989423 / __s_;
131 double __b1 = .4166667E-1 / __mean_;
132 double __b2 = .3 * __b1 * __b1;
133 __c3_ = .1428571 * __b1 * __b2;
134 __c2_ = __b2 - 15. * __c3_;
135 __c1_ = __b1 - 6. * __b2 + 45. * __c3_;
136 __c0_ = 1. - __b1 + 3. * __b2 - 15. * __c3_;
137 __c_ = .1069 / __mean_;
138 }
139}
140
141template <class _IntType>
142template <class _URNG>
143_IntType poisson_distribution<_IntType>::operator()(_URNG& __urng, const param_type& __pr) {
144 static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
145 double __tx;
146 uniform_real_distribution<double> __urd;
147 if (__pr.__mean_ < 10) {
148 __tx = 0;
149 for (double __p = __urd(__urng); __p > __pr.__l_; ++__tx)
150 __p *= __urd(__urng);
151 } else {
152 double __difmuk;
153 double __g = __pr.__mean_ + __pr.__s_ * normal_distribution<double>()(__urng);
154 double __u;
155 if (__g > 0) {
156 __tx = __math::trunc(x: __g);
157 if (__tx >= __pr.__l_)
158 return std::__clamp_to_integral<result_type>(__tx);
159 __difmuk = __pr.__mean_ - __tx;
160 __u = __urd(__urng);
161 if (__pr.__d_ * __u >= __difmuk * __difmuk * __difmuk)
162 return std::__clamp_to_integral<result_type>(__tx);
163 }
164 exponential_distribution<double> __edist;
165 for (bool __using_exp_dist = false; true; __using_exp_dist = true) {
166 double __e;
167 if (__using_exp_dist || __g <= 0) {
168 double __t;
169 do {
170 __e = __edist(__urng);
171 __u = __urd(__urng);
172 __u += __u - 1;
173 __t = 1.8 + (__u < 0 ? -__e : __e);
174 } while (__t <= -.6744);
175 __tx = __math::trunc(__pr.__mean_ + __pr.__s_ * __t);
176 __difmuk = __pr.__mean_ - __tx;
177 __using_exp_dist = true;
178 }
179 double __px;
180 double __py;
181 if (__tx < 10 && __tx >= 0) {
182 const double __fac[] = {1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880};
183 __px = -__pr.__mean_;
184 __py = __math::pow(__pr.__mean_, (double)__tx) / __fac[static_cast<int>(__tx)];
185 } else {
186 double __del = .8333333E-1 / __tx;
187 __del -= 4.8 * __del * __del * __del;
188 double __v = __difmuk / __tx;
189 if (__math::abs(x: __v) > 0.25)
190 __px = __tx * __math::log(x: 1 + __v) - __difmuk - __del;
191 else
192 __px = __tx * __v * __v *
193 (((((((.1250060 * __v + -.1384794) * __v + .1421878) * __v + -.1661269) * __v + .2000118) * __v +
194 -.2500068) *
195 __v +
196 .3333333) *
197 __v +
198 -.5) -
199 __del;
200 __py = .3989423 / __math::sqrt(x: __tx);
201 }
202 double __r = (0.5 - __difmuk) / __pr.__s_;
203 double __r2 = __r * __r;
204 double __fx = -0.5 * __r2;
205 double __fy = __pr.__omega_ * (((__pr.__c3_ * __r2 + __pr.__c2_) * __r2 + __pr.__c1_) * __r2 + __pr.__c0_);
206 if (__using_exp_dist) {
207 if (__pr.__c_ * __math::abs(x: __u) <= __py * __math::exp(x: __px + __e) - __fy * __math::exp(x: __fx + __e))
208 break;
209 } else {
210 if (__fy - __u * __fy <= __py * __math::exp(x: __px - __fx))
211 break;
212 }
213 }
214 }
215 return std::__clamp_to_integral<result_type>(__tx);
216}
217
218template <class _CharT, class _Traits, class _IntType>
219_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
220operator<<(basic_ostream<_CharT, _Traits>& __os, const poisson_distribution<_IntType>& __x) {
221 __save_flags<_CharT, _Traits> __lx(__os);
222 typedef basic_ostream<_CharT, _Traits> _OStream;
223 __os.flags(_OStream::dec | _OStream::left | _OStream::fixed | _OStream::scientific);
224 return __os << __x.mean();
225}
226
227template <class _CharT, class _Traits, class _IntType>
228_LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
229operator>>(basic_istream<_CharT, _Traits>& __is, poisson_distribution<_IntType>& __x) {
230 typedef poisson_distribution<_IntType> _Eng;
231 typedef typename _Eng::param_type param_type;
232 __save_flags<_CharT, _Traits> __lx(__is);
233 typedef basic_istream<_CharT, _Traits> _Istream;
234 __is.flags(_Istream::dec | _Istream::skipws);
235 double __mean;
236 __is >> __mean;
237 if (!__is.fail())
238 __x.param(param_type(__mean));
239 return __is;
240}
241
242_LIBCPP_END_NAMESPACE_STD
243
244_LIBCPP_POP_MACROS
245
246#endif // _LIBCPP___RANDOM_POISSON_DISTRIBUTION_H
247