v1/__random/exponential_distribution.h

0001 //===----------------------------------------------------------------------===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008
0009 #ifndef _LIBCPP___RANDOM_EXPONENTIAL_DISTRIBUTION_H
0010 #define _LIBCPP___RANDOM_EXPONENTIAL_DISTRIBUTION_H
0011
0012 #include <__config>
0013 #include <__random/generate_canonical.h>
0014 #include <__random/is_valid.h>
0015 #include <__random/uniform_real_distribution.h>
0016 #include <cmath>
0017 #include <iosfwd>
0018 #include <limits>
0019
0020 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0021 #  pragma GCC system_header
0022 #endif
0023
0024 _LIBCPP_PUSH_MACROS
0025 #include <__undef_macros>
0026
0027 _LIBCPP_BEGIN_NAMESPACE_STD
0028
0029 template <class _RealType = double>
0030 class _LIBCPP_TEMPLATE_VIS exponential_distribution {
0031   static_assert(__libcpp_random_is_valid_realtype<_RealType>::value,
0032                 "RealType must be a supported floating-point type");
0033
0034 public:
0035   // types
0036   typedef _RealType result_type;
0037
0038   class _LIBCPP_TEMPLATE_VIS param_type {
0039     result_type __lambda_;
0040
0041   public:
0042     typedef exponential_distribution distribution_type;
0043
0044     _LIBCPP_HIDE_FROM_ABI explicit param_type(result_type __lambda = 1) : __lambda_(__lambda) {}
0045
0046     _LIBCPP_HIDE_FROM_ABI result_type lambda() const { return __lambda_; }
0047
0048     friend _LIBCPP_HIDE_FROM_ABI bool operator==(const param_type& __x, const param_type& __y) {
0049       return __x.__lambda_ == __y.__lambda_;
0050     }
0051     friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const param_type& __x, const param_type& __y) { return !(__x == __y); }
0052   };
0053
0054 private:
0055   param_type __p_;
0056
0057 public:
0058   // constructors and reset functions
0059 #ifndef _LIBCPP_CXX03_LANG
0060   _LIBCPP_HIDE_FROM_ABI exponential_distribution() : exponential_distribution(1) {}
0061   _LIBCPP_HIDE_FROM_ABI explicit exponential_distribution(result_type __lambda) : __p_(param_type(__lambda)) {}
0062 #else
0063   _LIBCPP_HIDE_FROM_ABI explicit exponential_distribution(result_type __lambda = 1) : __p_(param_type(__lambda)) {}
0064 #endif
0065   _LIBCPP_HIDE_FROM_ABI explicit exponential_distribution(const param_type& __p) : __p_(__p) {}
0066   _LIBCPP_HIDE_FROM_ABI void reset() {}
0067
0068   // generating functions
0069   template <class _URNG>
0070   _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g) {
0071     return (*this)(__g, __p_);
0072   }
0073   template <class _URNG>
0074   _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
0075
0076   // property functions
0077   _LIBCPP_HIDE_FROM_ABI result_type lambda() const { return __p_.lambda(); }
0078
0079   _LIBCPP_HIDE_FROM_ABI param_type param() const { return __p_; }
0080   _LIBCPP_HIDE_FROM_ABI void param(const param_type& __p) { __p_ = __p; }
0081
0082   _LIBCPP_HIDE_FROM_ABI result_type min() const { return 0; }
0083   _LIBCPP_HIDE_FROM_ABI result_type max() const { return numeric_limits<result_type>::infinity(); }
0084
0085   friend _LIBCPP_HIDE_FROM_ABI bool
0086   operator==(const exponential_distribution& __x, const exponential_distribution& __y) {
0087     return __x.__p_ == __y.__p_;
0088   }
0089   friend _LIBCPP_HIDE_FROM_ABI bool
0090   operator!=(const exponential_distribution& __x, const exponential_distribution& __y) {
0091     return !(__x == __y);
0092   }
0093 };
0094
0095 template <class _RealType>
0096 template <class _URNG>
0097 _RealType exponential_distribution<_RealType>::operator()(_URNG& __g, const param_type& __p) {
0098   static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
0099   return -std::log(result_type(1) - std::generate_canonical<result_type, numeric_limits<result_type>::digits>(__g)) /
0100          __p.lambda();
0101 }
0102
0103 template <class _CharT, class _Traits, class _RealType>
0104 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
0105 operator<<(basic_ostream<_CharT, _Traits>& __os, const exponential_distribution<_RealType>& __x) {
0106   __save_flags<_CharT, _Traits> __lx(__os);
0107   typedef basic_ostream<_CharT, _Traits> _OStream;
0108   __os.flags(_OStream::dec | _OStream::left | _OStream::fixed | _OStream::scientific);
0109   return __os << __x.lambda();
0110 }
0111
0112 template <class _CharT, class _Traits, class _RealType>
0113 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
0114 operator>>(basic_istream<_CharT, _Traits>& __is, exponential_distribution<_RealType>& __x) {
0115   typedef exponential_distribution<_RealType> _Eng;
0116   typedef typename _Eng::result_type result_type;
0117   typedef typename _Eng::param_type param_type;
0118   __save_flags<_CharT, _Traits> __lx(__is);
0119   typedef basic_istream<_CharT, _Traits> _Istream;
0120   __is.flags(_Istream::dec | _Istream::skipws);
0121   result_type __lambda;
0122   __is >> __lambda;
0123   if (!__is.fail())
0124     __x.param(param_type(__lambda));
0125   return __is;
0126 }
0127
0128 _LIBCPP_END_NAMESPACE_STD
0129
0130 _LIBCPP_POP_MACROS
0131
0132 #endif // _LIBCPP___RANDOM_EXPONENTIAL_DISTRIBUTION_H