v1/__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___RANDOM_BINOMIAL_DISTRIBUTION_H
0010 #define _LIBCPP___RANDOM_BINOMIAL_DISTRIBUTION_H
0011
0012 #include <__config>
0013 #include <__random/is_valid.h>
0014 #include <__random/uniform_real_distribution.h>
0015 #include <cmath>
0016 #include <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 <__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 // The LLVM C library provides this with conflicting `noexcept` attributes.
0101 #if !defined(_LIBCPP_MSVCRT_LIKE) && !defined(__LLVM_LIBC__)
0102 extern "C" double lgamma_r(double, int*);
0103 #endif
0104
0105 inline _LIBCPP_HIDE_FROM_ABI double __libcpp_lgamma(double __d) {
0106 #if defined(_LIBCPP_MSVCRT_LIKE) || defined(__LLVM_LIBC__)
0107   return lgamma(__d);
0108 #else
0109   int __sign;
0110   return lgamma_r(__d, &__sign);
0111 #endif
0112 }
0113
0114 template <class _IntType>
0115 binomial_distribution<_IntType>::param_type::param_type(result_type __t, double __p) : __t_(__t), __p_(__p) {
0116   if (0 < __p_ && __p_ < 1) {
0117     __r0_ = static_cast<result_type>((__t_ + 1) * __p_);
0118     __pr_ = std::exp(
0119         std::__libcpp_lgamma(__t_ + 1.) - std::__libcpp_lgamma(__r0_ + 1.) - std::__libcpp_lgamma(__t_ - __r0_ + 1.) +
0120         __r0_ * std::log(__p_) + (__t_ - __r0_) * std::log(1 - __p_));
0121     __odds_ratio_ = __p_ / (1 - __p_);
0122   }
0123 }
0124
0125 // Reference: Kemp, C.D. (1986). `A modal method for generating binomial
0126 //           variables', Commun. Statist. - Theor. Meth. 15(3), 805-813.
0127 template <class _IntType>
0128 template <class _URNG>
0129 _IntType binomial_distribution<_IntType>::operator()(_URNG& __g, const param_type& __pr) {
0130   static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
0131   if (__pr.__t_ == 0 || __pr.__p_ == 0)
0132     return 0;
0133   if (__pr.__p_ == 1)
0134     return __pr.__t_;
0135   uniform_real_distribution<double> __gen;
0136   double __u = __gen(__g) - __pr.__pr_;
0137   if (__u < 0)
0138     return __pr.__r0_;
0139   double __pu      = __pr.__pr_;
0140   double __pd      = __pu;
0141   result_type __ru = __pr.__r0_;
0142   result_type __rd = __ru;
0143   while (true) {
0144     bool __break = true;
0145     if (__rd >= 1) {
0146       __pd *= __rd / (__pr.__odds_ratio_ * (__pr.__t_ - __rd + 1));
0147       __u -= __pd;
0148       __break = false;
0149       if (__u < 0)
0150         return __rd - 1;
0151     }
0152     if (__rd != 0)
0153       --__rd;
0154     ++__ru;
0155     if (__ru <= __pr.__t_) {
0156       __pu *= (__pr.__t_ - __ru + 1) * __pr.__odds_ratio_ / __ru;
0157       __u -= __pu;
0158       __break = false;
0159       if (__u < 0)
0160         return __ru;
0161     }
0162     if (__break)
0163       return 0;
0164   }
0165 }
0166
0167 template <class _CharT, class _Traits, class _IntType>
0168 _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
0169 operator<<(basic_ostream<_CharT, _Traits>& __os, const binomial_distribution<_IntType>& __x) {
0170   __save_flags<_CharT, _Traits> __lx(__os);
0171   typedef basic_ostream<_CharT, _Traits> _OStream;
0172   __os.flags(_OStream::dec | _OStream::left | _OStream::fixed | _OStream::scientific);
0173   _CharT __sp = __os.widen(' ');
0174   __os.fill(__sp);
0175   return __os << __x.t() << __sp << __x.p();
0176 }
0177
0178 template <class _CharT, class _Traits, class _IntType>
0179 _LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
0180 operator>>(basic_istream<_CharT, _Traits>& __is, binomial_distribution<_IntType>& __x) {
0181   typedef binomial_distribution<_IntType> _Eng;
0182   typedef typename _Eng::result_type result_type;
0183   typedef typename _Eng::param_type param_type;
0184   __save_flags<_CharT, _Traits> __lx(__is);
0185   typedef basic_istream<_CharT, _Traits> _Istream;
0186   __is.flags(_Istream::dec | _Istream::skipws);
0187   result_type __t;
0188   double __p;
0189   __is >> __t >> __p;
0190   if (!__is.fail())
0191     __x.param(param_type(__t, __p));
0192   return __is;
0193 }
0194
0195 _LIBCPP_END_NAMESPACE_STD
0196
0197 _LIBCPP_POP_MACROS
0198
0199 #endif // _LIBCPP___RANDOM_BINOMIAL_DISTRIBUTION_H