__cxx03/__random/negative_binomial_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___CXX03___RANDOM_NEGATIVE_BINOMIAL_DISTRIBUTION_H
0010 #define _LIBCPP___CXX03___RANDOM_NEGATIVE_BINOMIAL_DISTRIBUTION_H
0011
0012 #include <__cxx03/__assert>
0013 #include <__cxx03/__config>
0014 #include <__cxx03/__random/bernoulli_distribution.h>
0015 #include <__cxx03/__random/gamma_distribution.h>
0016 #include <__cxx03/__random/is_valid.h>
0017 #include <__cxx03/__random/poisson_distribution.h>
0018 #include <__cxx03/iosfwd>
0019 #include <__cxx03/limits>
0020
0021 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0022 #  pragma GCC system_header
0023 #endif
0024
0025 _LIBCPP_PUSH_MACROS
0026 #include <__cxx03/__undef_macros>
0027
0028 _LIBCPP_BEGIN_NAMESPACE_STD
0029
0030 template <class _IntType = int>
0031 class _LIBCPP_TEMPLATE_VIS negative_binomial_distribution {
0032   static_assert(__libcpp_random_is_valid_inttype<_IntType>::value, "IntType must be a supported integer type");
0033
0034 public:
0035   // types
0036   typedef _IntType result_type;
0037
0038   class _LIBCPP_TEMPLATE_VIS param_type {
0039     result_type __k_;
0040     double __p_;
0041
0042   public:
0043     typedef negative_binomial_distribution distribution_type;
0044
0045     _LIBCPP_HIDE_FROM_ABI explicit param_type(result_type __k = 1, double __p = 0.5) : __k_(__k), __p_(__p) {}
0046
0047     _LIBCPP_HIDE_FROM_ABI result_type k() const { return __k_; }
0048     _LIBCPP_HIDE_FROM_ABI double p() const { return __p_; }
0049
0050     friend _LIBCPP_HIDE_FROM_ABI bool operator==(const param_type& __x, const param_type& __y) {
0051       return __x.__k_ == __y.__k_ && __x.__p_ == __y.__p_;
0052     }
0053     friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const param_type& __x, const param_type& __y) { return !(__x == __y); }
0054   };
0055
0056 private:
0057   param_type __p_;
0058
0059 public:
0060   // constructor and reset functions
0061 #ifndef _LIBCPP_CXX03_LANG
0062   _LIBCPP_HIDE_FROM_ABI negative_binomial_distribution() : negative_binomial_distribution(1) {}
0063   _LIBCPP_HIDE_FROM_ABI explicit negative_binomial_distribution(result_type __k, double __p = 0.5) : __p_(__k, __p) {}
0064 #else
0065   _LIBCPP_HIDE_FROM_ABI explicit negative_binomial_distribution(result_type __k = 1, double __p = 0.5)
0066       : __p_(__k, __p) {}
0067 #endif
0068   _LIBCPP_HIDE_FROM_ABI explicit negative_binomial_distribution(const param_type& __p) : __p_(__p) {}
0069   _LIBCPP_HIDE_FROM_ABI void reset() {}
0070
0071   // generating functions
0072   template <class _URNG>
0073   _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g) {
0074     return (*this)(__g, __p_);
0075   }
0076   template <class _URNG>
0077   _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
0078
0079   // property functions
0080   _LIBCPP_HIDE_FROM_ABI result_type k() const { return __p_.k(); }
0081   _LIBCPP_HIDE_FROM_ABI double p() const { return __p_.p(); }
0082
0083   _LIBCPP_HIDE_FROM_ABI param_type param() const { return __p_; }
0084   _LIBCPP_HIDE_FROM_ABI void param(const param_type& __p) { __p_ = __p; }
0085
0086   _LIBCPP_HIDE_FROM_ABI result_type min() const { return 0; }
0087   _LIBCPP_HIDE_FROM_ABI result_type max() const { return numeric_limits<result_type>::max(); }
0088
0089   friend _LIBCPP_HIDE_FROM_ABI bool
0090   operator==(const negative_binomial_distribution& __x, const negative_binomial_distribution& __y) {
0091     return __x.__p_ == __y.__p_;
0092   }
0093   friend _LIBCPP_HIDE_FROM_ABI bool
0094   operator!=(const negative_binomial_distribution& __x, const negative_binomial_distribution& __y) {
0095     return !(__x == __y);
0096   }
0097 };
0098
0099 template <class _IntType>
0100 template <class _URNG>
0101 _IntType negative_binomial_distribution<_IntType>::operator()(_URNG& __urng, const param_type& __pr) {
0102   static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
0103   result_type __k = __pr.k();
0104   double __p      = __pr.p();
0105   // When the number of bits in _IntType is small, we are too likely to
0106   // overflow __f below to use this technique.
0107   if (__k <= 21 * __p && sizeof(_IntType) > 1) {
0108     bernoulli_distribution __gen(__p);
0109     result_type __f = 0;
0110     result_type __s = 0;
0111     while (__s < __k) {
0112       if (__gen(__urng))
0113         ++__s;
0114       else
0115         ++__f;
0116     }
0117     _LIBCPP_ASSERT_INTERNAL(__f >= 0,
0118                             "std::negative_binomial_distribution should never produce negative values. "
0119                             "This is almost certainly a signed integer overflow issue on __f.");
0120     return __f;
0121   }
0122   return poisson_distribution<result_type>(gamma_distribution<double>(__k, (1 - __p) / __p)(__urng))(__urng);
0123 }
0124
0125 template <class _CharT, class _Traits, class _IntType>
0126 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
0127 operator<<(basic_ostream<_CharT, _Traits>& __os, const negative_binomial_distribution<_IntType>& __x) {
0128   __save_flags<_CharT, _Traits> __lx(__os);
0129   typedef basic_ostream<_CharT, _Traits> _OStream;
0130   __os.flags(_OStream::dec | _OStream::left | _OStream::fixed | _OStream::scientific);
0131   _CharT __sp = __os.widen(' ');
0132   __os.fill(__sp);
0133   return __os << __x.k() << __sp << __x.p();
0134 }
0135
0136 template <class _CharT, class _Traits, class _IntType>
0137 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
0138 operator>>(basic_istream<_CharT, _Traits>& __is, negative_binomial_distribution<_IntType>& __x) {
0139   typedef negative_binomial_distribution<_IntType> _Eng;
0140   typedef typename _Eng::result_type result_type;
0141   typedef typename _Eng::param_type param_type;
0142   __save_flags<_CharT, _Traits> __lx(__is);
0143   typedef basic_istream<_CharT, _Traits> _Istream;
0144   __is.flags(_Istream::dec | _Istream::skipws);
0145   result_type __k;
0146   double __p;
0147   __is >> __k >> __p;
0148   if (!__is.fail())
0149     __x.param(param_type(__k, __p));
0150   return __is;
0151 }
0152
0153 _LIBCPP_END_NAMESPACE_STD
0154
0155 _LIBCPP_POP_MACROS
0156
0157 #endif // _LIBCPP___CXX03___RANDOM_NEGATIVE_BINOMIAL_DISTRIBUTION_H