libcxx/include/__cxx03/__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___CXX03___RANDOM_EXPONENTIAL_DISTRIBUTION_H
  10 #define _LIBCPP___CXX03___RANDOM_EXPONENTIAL_DISTRIBUTION_H
  11
  12 #include <__cxx03/__config>
  13 #include <__cxx03/__random/generate_canonical.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_header
  22 #endif
  23
  24 _LIBCPP_PUSH_MACROS
  25 #include <__cxx03/__undef_macros>
  26
  27 _LIBCPP_BEGIN_NAMESPACE_STD
  28
  29 template <class _RealType = double>
  30 class _LIBCPP_TEMPLATE_VIS exponential_distribution {
  31   static_assert(__libcpp_random_is_valid_realtype<_RealType>::value,
  32                 "RealType must be a supported floating-point type");
  33
  34 public:
  35   // types
  36   typedef _RealType result_type;
  37
  38   class _LIBCPP_TEMPLATE_VIS param_type {
  39     result_type __lambda_;
  40
  41   public:
  42     typedef exponential_distribution distribution_type;
  43
  44     _LIBCPP_HIDE_FROM_ABI explicit param_type(result_type __lambda = 1) : __lambda_(__lambda) {}
  45
  46     _LIBCPP_HIDE_FROM_ABI result_type lambda() const { return __lambda_; }
  47
  48     friend _LIBCPP_HIDE_FROM_ABI bool operator==(const param_type& __x, const param_type& __y) {
  49       return __x.__lambda_ == __y.__lambda_;
  50     }
  51     friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const param_type& __x, const param_type& __y) { return !(__x == __y); }
  52   };
  53
  54 private:
  55   param_type __p_;
  56
  57 public:
  58   // constructors and reset functions
  59 #ifndef _LIBCPP_CXX03_LANG
  60   _LIBCPP_HIDE_FROM_ABI exponential_distribution() : exponential_distribution(1) {}
  61   _LIBCPP_HIDE_FROM_ABI explicit exponential_distribution(result_type __lambda) : __p_(param_type(__lambda)) {}
  62 #else
  63   _LIBCPP_HIDE_FROM_ABI explicit exponential_distribution(result_type __lambda = 1) : __p_(param_type(__lambda)) {}
  64 #endif
  65   _LIBCPP_HIDE_FROM_ABI explicit exponential_distribution(const param_type& __p) : __p_(__p) {}
  66   _LIBCPP_HIDE_FROM_ABI void reset() {}
  67
  68   // generating functions
  69   template <class _URNG>
  70   _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g) {
  71     return (*this)(__g, __p_);
  72   }
  73   template <class _URNG>
  74   _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
  75
  76   // property functions
  77   _LIBCPP_HIDE_FROM_ABI result_type lambda() const { return __p_.lambda(); }
  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
  86   operator==(const exponential_distribution& __x, const exponential_distribution& __y) {
  87     return __x.__p_ == __y.__p_;
  88   }
  89   friend _LIBCPP_HIDE_FROM_ABI bool
  90   operator!=(const exponential_distribution& __x, const exponential_distribution& __y) {
  91     return !(__x == __y);
  92   }
  93 };
  94
  95 template <class _RealType>
  96 template <class _URNG>
  97 _RealType exponential_distribution<_RealType>::operator()(_URNG& __g, const param_type& __p) {
  98   static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
  99   return -std::log(result_type(1) - std::generate_canonical<result_type, numeric_limits<result_type>::digits>(__g)) /
 100          __p.lambda();
 101 }
 102
 103 template <class _CharT, class _Traits, class _RealType>
 104 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
 105 operator<<(basic_ostream<_CharT, _Traits>& __os, const exponential_distribution<_RealType>& __x) {
 106   __save_flags<_CharT, _Traits> __lx(__os);
 107   typedef basic_ostream<_CharT, _Traits> _OStream;
 108   __os.flags(_OStream::dec | _OStream::left | _OStream::fixed | _OStream::scientific);
 109   return __os << __x.lambda();
 110 }
 111
 112 template <class _CharT, class _Traits, class _RealType>
 113 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
 114 operator>>(basic_istream<_CharT, _Traits>& __is, exponential_distribution<_RealType>& __x) {
 115   typedef exponential_distribution<_RealType> _Eng;
 116   typedef typename _Eng::result_type result_type;
 117   typedef typename _Eng::param_type param_type;
 118   __save_flags<_CharT, _Traits> __lx(__is);
 119   typedef basic_istream<_CharT, _Traits> _Istream;
 120   __is.flags(_Istream::dec | _Istream::skipws);
 121   result_type __lambda;
 122   __is >> __lambda;
 123   if (!__is.fail())
 124     __x.param(param_type(__lambda));
 125   return __is;
 126 }
 127
 128 _LIBCPP_END_NAMESPACE_STD
 129
 130 _LIBCPP_POP_MACROS
 131
 132 #endif // _LIBCPP___CXX03___RANDOM_EXPONENTIAL_DISTRIBUTION_H