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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-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP___CXX03___RANDOM_GAMMA_DISTRIBUTION_H10#define _LIBCPP___CXX03___RANDOM_GAMMA_DISTRIBUTION_H11 12#include <__cxx03/__config>13#include <__cxx03/__random/exponential_distribution.h>14#include <__cxx03/__random/is_valid.h>15#include <__cxx03/__random/uniform_real_distribution.h>16#include <__cxx03/cmath>17#include <__cxx03/iosfwd>18#include <__cxx03/limits>19 20#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)21# pragma GCC system_header22#endif23 24_LIBCPP_PUSH_MACROS25#include <__cxx03/__undef_macros>26 27_LIBCPP_BEGIN_NAMESPACE_STD28 29template <class _RealType = double>30class _LIBCPP_TEMPLATE_VIS gamma_distribution {31 static_assert(__libcpp_random_is_valid_realtype<_RealType>::value,32 "RealType must be a supported floating-point type");33 34public:35 // types36 typedef _RealType result_type;37 38 class _LIBCPP_TEMPLATE_VIS param_type {39 result_type __alpha_;40 result_type __beta_;41 42 public:43 typedef gamma_distribution distribution_type;44 45 _LIBCPP_HIDE_FROM_ABI explicit param_type(result_type __alpha = 1, result_type __beta = 1)46 : __alpha_(__alpha), __beta_(__beta) {}47 48 _LIBCPP_HIDE_FROM_ABI result_type alpha() const { return __alpha_; }49 _LIBCPP_HIDE_FROM_ABI result_type beta() const { return __beta_; }50 51 friend _LIBCPP_HIDE_FROM_ABI bool operator==(const param_type& __x, const param_type& __y) {52 return __x.__alpha_ == __y.__alpha_ && __x.__beta_ == __y.__beta_;53 }54 friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const param_type& __x, const param_type& __y) { return !(__x == __y); }55 };56 57private:58 param_type __p_;59 60public:61 // constructors and reset functions62 _LIBCPP_HIDE_FROM_ABI explicit gamma_distribution(result_type __alpha = 1, result_type __beta = 1)63 : __p_(param_type(__alpha, __beta)) {}64 _LIBCPP_HIDE_FROM_ABI explicit gamma_distribution(const param_type& __p) : __p_(__p) {}65 _LIBCPP_HIDE_FROM_ABI void reset() {}66 67 // generating functions68 template <class _URNG>69 _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g) {70 return (*this)(__g, __p_);71 }72 template <class _URNG>73 _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);74 75 // property functions76 _LIBCPP_HIDE_FROM_ABI result_type alpha() const { return __p_.alpha(); }77 _LIBCPP_HIDE_FROM_ABI result_type beta() const { return __p_.beta(); }78 79 _LIBCPP_HIDE_FROM_ABI param_type param() const { return __p_; }80 _LIBCPP_HIDE_FROM_ABI void param(const param_type& __p) { __p_ = __p; }81 82 _LIBCPP_HIDE_FROM_ABI result_type min() const { return 0; }83 _LIBCPP_HIDE_FROM_ABI result_type max() const { return numeric_limits<result_type>::infinity(); }84 85 friend _LIBCPP_HIDE_FROM_ABI bool operator==(const gamma_distribution& __x, const gamma_distribution& __y) {86 return __x.__p_ == __y.__p_;87 }88 friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const gamma_distribution& __x, const gamma_distribution& __y) {89 return !(__x == __y);90 }91};92 93template <class _RealType>94template <class _URNG>95_RealType gamma_distribution<_RealType>::operator()(_URNG& __g, const param_type& __p) {96 static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");97 result_type __a = __p.alpha();98 uniform_real_distribution<result_type> __gen(0, 1);99 exponential_distribution<result_type> __egen;100 result_type __x;101 if (__a == 1)102 __x = __egen(__g);103 else if (__a > 1) {104 const result_type __b = __a - 1;105 const result_type __c = 3 * __a - result_type(0.75);106 while (true) {107 const result_type __u = __gen(__g);108 const result_type __v = __gen(__g);109 const result_type __w = __u * (1 - __u);110 if (__w != 0) {111 const result_type __y = std::sqrt(__c / __w) * (__u - result_type(0.5));112 __x = __b + __y;113 if (__x >= 0) {114 const result_type __z = 64 * __w * __w * __w * __v * __v;115 if (__z <= 1 - 2 * __y * __y / __x)116 break;117 if (std::log(__z) <= 2 * (__b * std::log(__x / __b) - __y))118 break;119 }120 }121 }122 } else // __a < 1123 {124 while (true) {125 const result_type __u = __gen(__g);126 const result_type __es = __egen(__g);127 if (__u <= 1 - __a) {128 __x = std::pow(__u, 1 / __a);129 if (__x <= __es)130 break;131 } else {132 const result_type __e = -std::log((1 - __u) / __a);133 __x = std::pow(1 - __a + __a * __e, 1 / __a);134 if (__x <= __e + __es)135 break;136 }137 }138 }139 return __x * __p.beta();140}141 142template <class _CharT, class _Traits, class _RT>143_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&144operator<<(basic_ostream<_CharT, _Traits>& __os, const gamma_distribution<_RT>& __x) {145 __save_flags<_CharT, _Traits> __lx(__os);146 typedef basic_ostream<_CharT, _Traits> _OStream;147 __os.flags(_OStream::dec | _OStream::left | _OStream::fixed | _OStream::scientific);148 _CharT __sp = __os.widen(' ');149 __os.fill(__sp);150 __os << __x.alpha() << __sp << __x.beta();151 return __os;152}153 154template <class _CharT, class _Traits, class _RT>155_LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&156operator>>(basic_istream<_CharT, _Traits>& __is, gamma_distribution<_RT>& __x) {157 typedef gamma_distribution<_RT> _Eng;158 typedef typename _Eng::result_type result_type;159 typedef typename _Eng::param_type param_type;160 __save_flags<_CharT, _Traits> __lx(__is);161 typedef basic_istream<_CharT, _Traits> _Istream;162 __is.flags(_Istream::dec | _Istream::skipws);163 result_type __alpha;164 result_type __beta;165 __is >> __alpha >> __beta;166 if (!__is.fail())167 __x.param(param_type(__alpha, __beta));168 return __is;169}170 171_LIBCPP_END_NAMESPACE_STD172 173_LIBCPP_POP_MACROS174 175#endif // _LIBCPP___CXX03___RANDOM_GAMMA_DISTRIBUTION_H176