llvm-project/libcxx/include/__random/negative_binomial_distribution.h

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___RANDOM_NEGATIVE_BINOMIAL_DISTRIBUTION_H
#define _LIBCPP___RANDOM_NEGATIVE_BINOMIAL_DISTRIBUTION_H

#include <__config>
#include <__random/bernoulli_distribution.h>
#include <__random/gamma_distribution.h>
#include <__random/is_valid.h>
#include <__random/poisson_distribution.h>
#include <iosfwd>
#include <limits>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

template<class _IntType = int>
class _LIBCPP_TEMPLATE_VIS negative_binomial_distribution
{
    static_assert(__libcpp_random_is_valid_inttype<_IntType>::value, "IntType must be a supported integer type");
public:
    // types
    typedef _IntType result_type;

    class _LIBCPP_TEMPLATE_VIS param_type
    {
        result_type __k_;
        double __p_;
    public:
        typedef negative_binomial_distribution distribution_type;

        _LIBCPP_INLINE_VISIBILITY
        explicit param_type(result_type __k = 1, double __p = 0.5)
            : __k_(__k), __p_(__p) {}

        _LIBCPP_INLINE_VISIBILITY
        result_type k() const {return __k_;}
        _LIBCPP_INLINE_VISIBILITY
        double p() const {return __p_;}

        friend _LIBCPP_INLINE_VISIBILITY
            bool operator==(const param_type& __x, const param_type& __y)
            {return __x.__k_ == __y.__k_ && __x.__p_ == __y.__p_;}
        friend _LIBCPP_INLINE_VISIBILITY
            bool operator!=(const param_type& __x, const param_type& __y)
            {return !(__x == __y);}
    };

private:
    param_type __p_;

public:
    // constructor and reset functions
#ifndef _LIBCPP_CXX03_LANG
    _LIBCPP_INLINE_VISIBILITY
    negative_binomial_distribution() : negative_binomial_distribution(1) {}
    _LIBCPP_INLINE_VISIBILITY
    explicit negative_binomial_distribution(result_type __k, double __p = 0.5)
        : __p_(__k, __p) {}
#else
    _LIBCPP_INLINE_VISIBILITY
    explicit negative_binomial_distribution(result_type __k = 1,
                                            double __p = 0.5)
        : __p_(__k, __p) {}
#endif
    _LIBCPP_INLINE_VISIBILITY
    explicit negative_binomial_distribution(const param_type& __p) : __p_(__p) {}
    _LIBCPP_INLINE_VISIBILITY
    void reset() {}

    // generating functions
    template<class _URNG>
        _LIBCPP_INLINE_VISIBILITY
        result_type operator()(_URNG& __g)
        {return (*this)(__g, __p_);}
    template<class _URNG> result_type operator()(_URNG& __g, const param_type& __p);

    // property functions
    _LIBCPP_INLINE_VISIBILITY
    result_type k() const {return __p_.k();}
    _LIBCPP_INLINE_VISIBILITY
    double p() const {return __p_.p();}

    _LIBCPP_INLINE_VISIBILITY
    param_type param() const {return __p_;}
    _LIBCPP_INLINE_VISIBILITY
    void param(const param_type& __p) {__p_ = __p;}

    _LIBCPP_INLINE_VISIBILITY
    result_type min() const {return 0;}
    _LIBCPP_INLINE_VISIBILITY
    result_type max() const {return numeric_limits<result_type>::max();}

    friend _LIBCPP_INLINE_VISIBILITY
        bool operator==(const negative_binomial_distribution& __x,
                        const negative_binomial_distribution& __y)
        {return __x.__p_ == __y.__p_;}
    friend _LIBCPP_INLINE_VISIBILITY
        bool operator!=(const negative_binomial_distribution& __x,
                        const negative_binomial_distribution& __y)
        {return !(__x == __y);}
};

template <class _IntType>
template<class _URNG>
_IntType
negative_binomial_distribution<_IntType>::operator()(_URNG& __urng, const param_type& __pr)
{
    static_assert(__libcpp_random_is_valid_urng<_URNG>::value, "");
    result_type __k = __pr.k();
    double __p = __pr.p();
    // When the number of bits in _IntType is small, we are too likely to
    // overflow __f below to use this technique.
    if (__k <= 21 * __p && sizeof(_IntType) > 1)
    {
        bernoulli_distribution __gen(__p);
        result_type __f = 0;
        result_type __s = 0;
        while (__s < __k)
        {
            if (__gen(__urng))
                ++__s;
            else
                ++__f;
        }
        _LIBCPP_ASSERT(__f >= 0, "std::negative_binomial_distribution should never produce negative values. "
                                 "This is almost certainly a signed integer overflow issue on __f.");
        return __f;
    }
    return poisson_distribution<result_type>(gamma_distribution<double>
                                            (__k, (1-__p)/__p)(__urng))(__urng);
}

template <class _CharT, class _Traits, class _IntType>
_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os,
           const negative_binomial_distribution<_IntType>& __x)
{
    __save_flags<_CharT, _Traits> __lx(__os);
    typedef basic_ostream<_CharT, _Traits> _OStream;
    __os.flags(_OStream::dec | _OStream::left | _OStream::fixed |
               _OStream::scientific);
    _CharT __sp = __os.widen(' ');
    __os.fill(__sp);
    return __os << __x.k() << __sp << __x.p();
}

template <class _CharT, class _Traits, class _IntType>
_LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is,
           negative_binomial_distribution<_IntType>& __x)
{
    typedef negative_binomial_distribution<_IntType> _Eng;
    typedef typename _Eng::result_type result_type;
    typedef typename _Eng::param_type param_type;
    __save_flags<_CharT, _Traits> __lx(__is);
    typedef basic_istream<_CharT, _Traits> _Istream;
    __is.flags(_Istream::dec | _Istream::skipws);
    result_type __k;
    double __p;
    __is >> __k >> __p;
    if (!__is.fail())
        __x.param(param_type(__k, __p));
    return __is;
}

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___RANDOM_NEGATIVE_BINOMIAL_DISTRIBUTION_H