__cxx03/__random/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_BINOMIAL_DISTRIBUTION_H
0010 #define _LIBCPP___CXX03___RANDOM_BINOMIAL_DISTRIBUTION_H
0011
0012 #include <__cxx03/__config>
0013 #include <__cxx03/__random/is_valid.h>
0014 #include <__cxx03/__random/uniform_real_distribution.h>
0015 #include <__cxx03/cmath>
0016 #include <__cxx03/iosfwd>
0017
0018 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0019 #  pragma GCC system_header
0020 #endif
0021
0022 _LIBCPP_PUSH_MACROS
0023 #include <__cxx03/__undef_macros>
0024
0025 _LIBCPP_BEGIN_NAMESPACE_STD
0026
0027 template <class _IntType = int>
0028 class _LIBCPP_TEMPLATE_VIS binomial_distribution {
0029   static_assert(__libcpp_random_is_valid_inttype<_IntType>::value, "IntType must be a supported integer type");
0030
0031 public:
0032   // types
0033   typedef _IntType result_type;
0034
0035   class _LIBCPP_TEMPLATE_VIS param_type {
0036     result_type __t_;
0037     double __p_;
0038     double __pr_;
0039     double __odds_ratio_;
0040     result_type __r0_;
0041
0042   public:
0043     typedef binomial_distribution distribution_type;
0044
0045     _LIBCPP_HIDE_FROM_ABI explicit param_type(result_type __t = 1, double __p = 0.5);
0046
0047     _LIBCPP_HIDE_FROM_ABI result_type t() const { return __t_; }
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.__t_ == __y.__t_ && __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     friend class binomial_distribution;
0056   };
0057
0058 private:
0059   param_type __p_;
0060
0061 public:
0062   // constructors and reset functions
0063 #ifndef _LIBCPP_CXX03_LANG
0064   _LIBCPP_HIDE_FROM_ABI binomial_distribution() : binomial_distribution(1) {}
0065   _LIBCPP_HIDE_FROM_ABI explicit binomial_distribution(result_type __t, double __p = 0.5)
0066       : __p_(param_type(__t, __p)) {}
0067 #else
0068   _LIBCPP_HIDE_FROM_ABI explicit binomial_distribution(result_type __t = 1, double __p = 0.5)
0069       : __p_(param_type(__t, __p)) {}
0070 #endif
0071   _LIBCPP_HIDE_FROM_ABI explicit binomial_distribution(const param_type& __p) : __p_(__p) {}
0072   _LIBCPP_HIDE_FROM_ABI void reset() {}
0073
0074   // generating functions
0075   template <class _URNG>
0076   _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g) {
0077     return (*this)(__g, __p_);
0078   }
0079   template <class _URNG>
0080   _LIBCPP_HIDE_FROM_ABI result_type operator()(_URNG& __g, const param_type& __p);
0081
0082   // property functions
0083   _LIBCPP_HIDE_FROM_ABI result_type t() const { return __p_.t(); }
0084   _LIBCPP_HIDE_FROM_ABI double p() const { return __p_.p(); }
0085
0086   _LIBCPP_HIDE_FROM_ABI param_type param() const { return __p_; }
0087   _LIBCPP_HIDE_FROM_ABI void param(const param_type& __p) { __p_ = __p; }
0088
0089   _LIBCPP_HIDE_FROM_ABI result_type min() const { return 0; }
0090   _LIBCPP_HIDE_FROM_ABI result_type max() const { return t(); }
0091
0092   friend _LIBCPP_HIDE_FROM_ABI bool operator==(const binomial_distribution& __x, const binomial_distribution& __y) {
0093     return __x.__p_ == __y.__p_;
0094   }
0095   friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const binomial_distribution& __x, const binomial_distribution& __y) {
0096     return !(__x == __y);
0097   }
0098 };
0099
0100 #ifndef _LIBCPP_MSVCRT_LIKE
0101 extern "C" double lgamma_r(double, int*);
0102 #endif
0103
0104 inline _LIBCPP_HIDE_FROM_ABI double __libcpp_lgamma(double __d) {
0105 #if defined(_LIBCPP_MSVCRT_LIKE)
0106   return lgamma(__d);
0107 #else
0108   int __sign;
0109   return lgamma_r(__d, &__sign);
0110 #endif
0111 }
0112
0113 template <class _IntType>
0114 binomial_distribution<_IntType>::param_type::param_type(result_type __t, double __p) : __t_(__t), __p_(__p) {
0115   if (0 < __p_ && __p_ < 1) {
0116     __r0_ = static_cast<result_type>((__t_ + 1) * __p_);
0117     __pr_ = std::exp(
0118         std::__libcpp_lgamma(__t_ + 1.) - std::__libcpp_lgamma(__r0_ + 1.) - std::__libcpp_lgamma(__t_ - __r0_ + 1.) +
0119         __r0_ * std::log(__p_) + (__t_ - __r0_) * std::log(1 - __p_));
0120     __odds_ratio_ = __p_ / (1 - __p_);
0121   }
0122 }
0123
0124 // Reference: Kemp, C.D. (1986). `A modal method for generating binomial
0125 //           variables', Commun. Statist. - Theor. Meth. 15(3), 805-813.
0126 template <class _IntType>
0127 template <class _URNG>
0128 _IntType binomial_distribution<_IntType>::operator()(_URNG& __g, const param_type& __pr) {
0129   static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
0130   if (__pr.__t_ == 0 || __pr.__p_ == 0)
0131     return 0;
0132   if (__pr.__p_ == 1)
0133     return __pr.__t_;
0134   uniform_real_distribution<double> __gen;
0135   double __u = __gen(__g) - __pr.__pr_;
0136   if (__u < 0)
0137     return __pr.__r0_;
0138   double __pu      = __pr.__pr_;
0139   double __pd      = __pu;
0140   result_type __ru = __pr.__r0_;
0141   result_type __rd = __ru;
0142   while (true) {
0143     bool __break = true;
0144     if (__rd >= 1) {
0145       __pd *= __rd / (__pr.__odds_ratio_ * (__pr.__t_ - __rd + 1));
0146       __u -= __pd;
0147       __break = false;
0148       if (__u < 0)
0149         return __rd - 1;
0150     }
0151     if (__rd != 0)
0152       --__rd;
0153     ++__ru;
0154     if (__ru <= __pr.__t_) {
0155       __pu *= (__pr.__t_ - __ru + 1) * __pr.__odds_ratio_ / __ru;
0156       __u -= __pu;
0157       __break = false;
0158       if (__u < 0)
0159         return __ru;
0160     }
0161     if (__break)
0162       return 0;
0163   }
0164 }
0165
0166 template <class _CharT, class _Traits, class _IntType>
0167 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
0168 operator<<(basic_ostream<_CharT, _Traits>& __os, const binomial_distribution<_IntType>& __x) {
0169   __save_flags<_CharT, _Traits> __lx(__os);
0170   typedef basic_ostream<_CharT, _Traits> _OStream;
0171   __os.flags(_OStream::dec | _OStream::left | _OStream::fixed | _OStream::scientific);
0172   _CharT __sp = __os.widen(' ');
0173   __os.fill(__sp);
0174   return __os << __x.t() << __sp << __x.p();
0175 }
0176
0177 template <class _CharT, class _Traits, class _IntType>
0178 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
0179 operator>>(basic_istream<_CharT, _Traits>& __is, binomial_distribution<_IntType>& __x) {
0180   typedef binomial_distribution<_IntType> _Eng;
0181   typedef typename _Eng::result_type result_type;
0182   typedef typename _Eng::param_type param_type;
0183   __save_flags<_CharT, _Traits> __lx(__is);
0184   typedef basic_istream<_CharT, _Traits> _Istream;
0185   __is.flags(_Istream::dec | _Istream::skipws);
0186   result_type __t;
0187   double __p;
0188   __is >> __t >> __p;
0189   if (!__is.fail())
0190     __x.param(param_type(__t, __p));
0191   return __is;
0192 }
0193
0194 _LIBCPP_END_NAMESPACE_STD
0195
0196 _LIBCPP_POP_MACROS
0197
0198 #endif // _LIBCPP___CXX03___RANDOM_BINOMIAL_DISTRIBUTION_H