libcxx/include/__random/binomial_distribution.h

   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_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>
  89     _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
  90
  91     // property functions
  92     _LIBCPP_INLINE_VISIBILITY
  93     result_type t() const {return __p_.t();}
  94     _LIBCPP_INLINE_VISIBILITY
  95     double p() const {return __p_.p();}
  96
  97     _LIBCPP_INLINE_VISIBILITY
  98     param_type param() const {return __p_;}
  99     _LIBCPP_INLINE_VISIBILITY
 100     void param(const param_type& __p) {__p_ = __p;}
 101
 102     _LIBCPP_INLINE_VISIBILITY
 103     result_type min() const {return 0;}
 104     _LIBCPP_INLINE_VISIBILITY
 105     result_type max() const {return t();}
 106
 107     friend _LIBCPP_INLINE_VISIBILITY
 108         bool operator==(const binomial_distribution& __x,
 109                         const binomial_distribution& __y)
 110         {return __x.__p_ == __y.__p_;}
 111     friend _LIBCPP_INLINE_VISIBILITY
 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_INLINE_VISIBILITY 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_ = _VSTD::exp(std::__libcpp_lgamma(__t_ + 1.) -
 138                            std::__libcpp_lgamma(__r0_ + 1.) -
 139                            std::__libcpp_lgamma(__t_ - __r0_ + 1.) + __r0_ * _VSTD::log(__p_) +
 140                            (__t_ - __r0_) * _VSTD::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