libcxx/include/__random/negative_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_NEGATIVE_BINOMIAL_DISTRIBUTION_H
  10 #define _LIBCPP___RANDOM_NEGATIVE_BINOMIAL_DISTRIBUTION_H
  11
  12 #include <__config>
  13 #include <__random/bernoulli_distribution.h>
  14 #include <__random/gamma_distribution.h>
  15 #include <__random/is_valid.h>
  16 #include <__random/poisson_distribution.h>
  17 #include <iosfwd>
  18 #include <limits>
  19
  20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  21 #  pragma GCC system_header
  22 #endif
  23
  24 _LIBCPP_PUSH_MACROS
  25 #include <__undef_macros>
  26
  27 _LIBCPP_BEGIN_NAMESPACE_STD
  28
  29 template<class _IntType = int>
  30 class _LIBCPP_TEMPLATE_VIS negative_binomial_distribution
  31 {
  32     static_assert(__libcpp_random_is_valid_inttype<_IntType>::value, "IntType must be a supported integer type");
  33 public:
  34     // types
  35     typedef _IntType result_type;
  36
  37     class _LIBCPP_TEMPLATE_VIS param_type
  38     {
  39         result_type __k_;
  40         double __p_;
  41     public:
  42         typedef negative_binomial_distribution distribution_type;
  43
  44         _LIBCPP_INLINE_VISIBILITY
  45         explicit param_type(result_type __k = 1, double __p = 0.5)
  46             : __k_(__k), __p_(__p) {}
  47
  48         _LIBCPP_INLINE_VISIBILITY
  49         result_type k() const {return __k_;}
  50         _LIBCPP_INLINE_VISIBILITY
  51         double p() const {return __p_;}
  52
  53         friend _LIBCPP_INLINE_VISIBILITY
  54             bool operator==(const param_type& __x, const param_type& __y)
  55             {return __x.__k_ == __y.__k_ && __x.__p_ == __y.__p_;}
  56         friend _LIBCPP_INLINE_VISIBILITY
  57             bool operator!=(const param_type& __x, const param_type& __y)
  58             {return !(__x == __y);}
  59     };
  60
  61 private:
  62     param_type __p_;
  63
  64 public:
  65     // constructor and reset functions
  66 #ifndef _LIBCPP_CXX03_LANG
  67     _LIBCPP_INLINE_VISIBILITY
  68     negative_binomial_distribution() : negative_binomial_distribution(1) {}
  69     _LIBCPP_INLINE_VISIBILITY
  70     explicit negative_binomial_distribution(result_type __k, double __p = 0.5)
  71         : __p_(__k, __p) {}
  72 #else
  73     _LIBCPP_INLINE_VISIBILITY
  74     explicit negative_binomial_distribution(result_type __k = 1,
  75                                             double __p = 0.5)
  76         : __p_(__k, __p) {}
  77 #endif
  78     _LIBCPP_INLINE_VISIBILITY
  79     explicit negative_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 k() const {return __p_.k();}
  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 numeric_limits<result_type>::max();}
 106
 107     friend _LIBCPP_INLINE_VISIBILITY
 108         bool operator==(const negative_binomial_distribution& __x,
 109                         const negative_binomial_distribution& __y)
 110         {return __x.__p_ == __y.__p_;}
 111     friend _LIBCPP_INLINE_VISIBILITY
 112         bool operator!=(const negative_binomial_distribution& __x,
 113                         const negative_binomial_distribution& __y)
 114         {return !(__x == __y);}
 115 };
 116
 117 template <class _IntType>
 118 template<class _URNG>
 119 _IntType
 120 negative_binomial_distribution<_IntType>::operator()(_URNG& __urng, const param_type& __pr)
 121 {
 122     static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
 123     result_type __k = __pr.k();
 124     double __p = __pr.p();
 125     // When the number of bits in _IntType is small, we are too likely to
 126     // overflow __f below to use this technique.
 127     if (__k <= 21 * __p && sizeof(_IntType) > 1)
 128     {
 129         bernoulli_distribution __gen(__p);
 130         result_type __f = 0;
 131         result_type __s = 0;
 132         while (__s < __k)
 133         {
 134             if (__gen(__urng))
 135                 ++__s;
 136             else
 137                 ++__f;
 138         }
 139         _LIBCPP_ASSERT_UNCATEGORIZED(__f >= 0,
 140                                      "std::negative_binomial_distribution should never produce negative values. "
 141                                      "This is almost certainly a signed integer overflow issue on __f.");
 142         return __f;
 143     }
 144     return poisson_distribution<result_type>(gamma_distribution<double>
 145                                             (__k, (1-__p)/__p)(__urng))(__urng);
 146 }
 147
 148 template <class _CharT, class _Traits, class _IntType>
 149 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
 150 operator<<(basic_ostream<_CharT, _Traits>& __os,
 151            const negative_binomial_distribution<_IntType>& __x)
 152 {
 153     __save_flags<_CharT, _Traits> __lx(__os);
 154     typedef basic_ostream<_CharT, _Traits> _OStream;
 155     __os.flags(_OStream::dec | _OStream::left | _OStream::fixed |
 156                _OStream::scientific);
 157     _CharT __sp = __os.widen(' ');
 158     __os.fill(__sp);
 159     return __os << __x.k() << __sp << __x.p();
 160 }
 161
 162 template <class _CharT, class _Traits, class _IntType>
 163 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
 164 operator>>(basic_istream<_CharT, _Traits>& __is,
 165            negative_binomial_distribution<_IntType>& __x)
 166 {
 167     typedef negative_binomial_distribution<_IntType> _Eng;
 168     typedef typename _Eng::result_type result_type;
 169     typedef typename _Eng::param_type param_type;
 170     __save_flags<_CharT, _Traits> __lx(__is);
 171     typedef basic_istream<_CharT, _Traits> _Istream;
 172     __is.flags(_Istream::dec | _Istream::skipws);
 173     result_type __k;
 174     double __p;
 175     __is >> __k >> __p;
 176     if (!__is.fail())
 177         __x.param(param_type(__k, __p));
 178     return __is;
 179 }
 180
 181 _LIBCPP_END_NAMESPACE_STD
 182
 183 _LIBCPP_POP_MACROS
 184
 185 #endif // _LIBCPP___RANDOM_NEGATIVE_BINOMIAL_DISTRIBUTION_H