libcxx/include/__random/exponential_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_EXPONENTIAL_DISTRIBUTION_H
  10 #define _LIBCPP___RANDOM_EXPONENTIAL_DISTRIBUTION_H
  11
  12 #include <__config>
  13 #include <__random/generate_canonical.h>
  14 #include <__random/is_valid.h>
  15 #include <__random/uniform_real_distribution.h>
  16 #include <cmath>
  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 _RealType = double>
  30 class _LIBCPP_TEMPLATE_VIS exponential_distribution
  31 {
  32 public:
  33     // types
  34     typedef _RealType result_type;
  35
  36     class _LIBCPP_TEMPLATE_VIS param_type
  37     {
  38         result_type __lambda_;
  39     public:
  40         typedef exponential_distribution distribution_type;
  41
  42         _LIBCPP_INLINE_VISIBILITY
  43         explicit param_type(result_type __lambda = 1) : __lambda_(__lambda) {}
  44
  45         _LIBCPP_INLINE_VISIBILITY
  46         result_type lambda() const {return __lambda_;}
  47
  48         friend _LIBCPP_INLINE_VISIBILITY
  49             bool operator==(const param_type& __x, const param_type& __y)
  50             {return __x.__lambda_ == __y.__lambda_;}
  51         friend _LIBCPP_INLINE_VISIBILITY
  52             bool operator!=(const param_type& __x, const param_type& __y)
  53             {return !(__x == __y);}
  54     };
  55
  56 private:
  57     param_type __p_;
  58
  59 public:
  60     // constructors and reset functions
  61 #ifndef _LIBCPP_CXX03_LANG
  62     _LIBCPP_INLINE_VISIBILITY
  63     exponential_distribution() : exponential_distribution(1) {}
  64     _LIBCPP_INLINE_VISIBILITY
  65     explicit exponential_distribution(result_type __lambda)
  66         : __p_(param_type(__lambda)) {}
  67 #else
  68     _LIBCPP_INLINE_VISIBILITY
  69     explicit exponential_distribution(result_type __lambda = 1)
  70         : __p_(param_type(__lambda)) {}
  71 #endif
  72     _LIBCPP_INLINE_VISIBILITY
  73     explicit exponential_distribution(const param_type& __p) : __p_(__p) {}
  74     _LIBCPP_INLINE_VISIBILITY
  75     void reset() {}
  76
  77     // generating functions
  78     template<class _URNG>
  79         _LIBCPP_INLINE_VISIBILITY
  80         result_type operator()(_URNG& __g)
  81         {return (*this)(__g, __p_);}
  82     template<class _URNG>
  83     _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
  84
  85     // property functions
  86     _LIBCPP_INLINE_VISIBILITY
  87     result_type lambda() const {return __p_.lambda();}
  88
  89     _LIBCPP_INLINE_VISIBILITY
  90     param_type param() const {return __p_;}
  91     _LIBCPP_INLINE_VISIBILITY
  92     void param(const param_type& __p) {__p_ = __p;}
  93
  94     _LIBCPP_INLINE_VISIBILITY
  95     result_type min() const {return 0;}
  96     _LIBCPP_INLINE_VISIBILITY
  97     result_type max() const {return numeric_limits<result_type>::infinity();}
  98
  99     friend _LIBCPP_INLINE_VISIBILITY
 100         bool operator==(const exponential_distribution& __x,
 101                         const exponential_distribution& __y)
 102         {return __x.__p_ == __y.__p_;}
 103     friend _LIBCPP_INLINE_VISIBILITY
 104         bool operator!=(const exponential_distribution& __x,
 105                         const exponential_distribution& __y)
 106         {return !(__x == __y);}
 107 };
 108
 109 template <class _RealType>
 110 template<class _URNG>
 111 _RealType
 112 exponential_distribution<_RealType>::operator()(_URNG& __g, const param_type& __p)
 113 {
 114     static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
 115     return -_VSTD::log
 116                   (
 117                       result_type(1) -
 118                       _VSTD::generate_canonical<result_type,
 119                                        numeric_limits<result_type>::digits>(__g)
 120                   )
 121                   / __p.lambda();
 122 }
 123
 124 template <class _CharT, class _Traits, class _RealType>
 125 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
 126 operator<<(basic_ostream<_CharT, _Traits>& __os,
 127            const exponential_distribution<_RealType>& __x)
 128 {
 129     __save_flags<_CharT, _Traits> __lx(__os);
 130     typedef basic_ostream<_CharT, _Traits> _OStream;
 131     __os.flags(_OStream::dec | _OStream::left | _OStream::fixed |
 132                _OStream::scientific);
 133     return __os << __x.lambda();
 134 }
 135
 136 template <class _CharT, class _Traits, class _RealType>
 137 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
 138 operator>>(basic_istream<_CharT, _Traits>& __is,
 139            exponential_distribution<_RealType>& __x)
 140 {
 141     typedef exponential_distribution<_RealType> _Eng;
 142     typedef typename _Eng::result_type result_type;
 143     typedef typename _Eng::param_type param_type;
 144     __save_flags<_CharT, _Traits> __lx(__is);
 145     typedef basic_istream<_CharT, _Traits> _Istream;
 146     __is.flags(_Istream::dec | _Istream::skipws);
 147     result_type __lambda;
 148     __is >> __lambda;
 149     if (!__is.fail())
 150         __x.param(param_type(__lambda));
 151     return __is;
 152 }
 153
 154 _LIBCPP_END_NAMESPACE_STD
 155
 156 _LIBCPP_POP_MACROS
 157
 158 #endif // _LIBCPP___RANDOM_EXPONENTIAL_DISTRIBUTION_H