//===----------------------------------------------------------------------===//
//
// 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_INDEPENDENT_BITS_ENGINE_H
#define _LIBCPP___RANDOM_INDEPENDENT_BITS_ENGINE_H

#include <__config>
#include <__random/is_seed_sequence.h>
#include <__random/log2.h>
#include <__type_traits/conditional.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/is_convertible.h>
#include <__utility/move.h>
#include <cstddef>
#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 _Engine, size_t __w, class _UIntType>
class _LIBCPP_TEMPLATE_VIS independent_bits_engine
{
    template <class _UInt, _UInt _R0, size_t _Wp, size_t _Mp>
    class __get_n
    {
        static _LIBCPP_CONSTEXPR const size_t _Dt = numeric_limits<_UInt>::digits;
        static _LIBCPP_CONSTEXPR const size_t _Np = _Wp / _Mp + (_Wp % _Mp != 0);
        static _LIBCPP_CONSTEXPR const size_t _W0 = _Wp / _Np;
        static _LIBCPP_CONSTEXPR const _UInt _Y0 = _W0 >= _Dt ? 0 : (_R0 >> _W0) << _W0;
    public:
        static _LIBCPP_CONSTEXPR const size_t value = _R0 - _Y0 > _Y0 / _Np ? _Np + 1 : _Np;
    };
public:
    // types
    typedef _UIntType result_type;

private:
    _Engine __e_;

    static _LIBCPP_CONSTEXPR const result_type _Dt = numeric_limits<result_type>::digits;
    static_assert(  0 <  __w, "independent_bits_engine invalid parameters");
    static_assert(__w <= _Dt, "independent_bits_engine invalid parameters");

    typedef typename _Engine::result_type _Engine_result_type;
    typedef __conditional_t<sizeof(_Engine_result_type) <= sizeof(result_type), result_type, _Engine_result_type>
        _Working_result_type;
#ifdef _LIBCPP_CXX03_LANG
    static const _Working_result_type _Rp = _Engine::_Max - _Engine::_Min
                                          + _Working_result_type(1);
#else
    static _LIBCPP_CONSTEXPR const _Working_result_type _Rp = _Engine::max() - _Engine::min()
                                                            + _Working_result_type(1);
#endif
    static _LIBCPP_CONSTEXPR const size_t __m = __log2<_Working_result_type, _Rp>::value;
    static _LIBCPP_CONSTEXPR const size_t __n = __get_n<_Working_result_type, _Rp, __w, __m>::value;
    static _LIBCPP_CONSTEXPR const size_t __w0 = __w / __n;
    static _LIBCPP_CONSTEXPR const size_t __n0 = __n - __w % __n;
    static _LIBCPP_CONSTEXPR const size_t _WDt = numeric_limits<_Working_result_type>::digits;
    static _LIBCPP_CONSTEXPR const size_t _EDt = numeric_limits<_Engine_result_type>::digits;
    static _LIBCPP_CONSTEXPR const _Working_result_type __y0 = __w0 >= _WDt ? 0 :
                                                               (_Rp >> __w0) << __w0;
    static _LIBCPP_CONSTEXPR const _Working_result_type __y1 = __w0 >= _WDt - 1 ? 0 :
                                                               (_Rp >> (__w0+1)) << (__w0+1);
    static _LIBCPP_CONSTEXPR const _Engine_result_type __mask0 = __w0 > 0 ?
                                _Engine_result_type(~0) >> (_EDt - __w0) :
                                _Engine_result_type(0);
    static _LIBCPP_CONSTEXPR const _Engine_result_type __mask1 = __w0 < _EDt - 1 ?
                                _Engine_result_type(~0) >> (_EDt - (__w0 + 1)) :
                                _Engine_result_type(~0);
public:
    static _LIBCPP_CONSTEXPR const result_type _Min = 0;
    static _LIBCPP_CONSTEXPR const result_type _Max = __w == _Dt ? result_type(~0) :
                                                      (result_type(1) << __w) - result_type(1);
    static_assert(_Min < _Max, "independent_bits_engine invalid parameters");

    // engine characteristics
    _LIBCPP_INLINE_VISIBILITY
    static _LIBCPP_CONSTEXPR result_type min() { return _Min; }
    _LIBCPP_INLINE_VISIBILITY
    static _LIBCPP_CONSTEXPR result_type max() { return _Max; }

    // constructors and seeding functions
    _LIBCPP_INLINE_VISIBILITY
    independent_bits_engine() {}
    _LIBCPP_INLINE_VISIBILITY
    explicit independent_bits_engine(const _Engine& __e)
        : __e_(__e) {}
#ifndef _LIBCPP_CXX03_LANG
    _LIBCPP_INLINE_VISIBILITY
    explicit independent_bits_engine(_Engine&& __e)
        : __e_(_VSTD::move(__e)) {}
#endif // _LIBCPP_CXX03_LANG
    _LIBCPP_INLINE_VISIBILITY
    explicit independent_bits_engine(result_type __sd) : __e_(__sd) {}
    template<class _Sseq>
        _LIBCPP_INLINE_VISIBILITY
        explicit independent_bits_engine(_Sseq& __q,
        typename enable_if<__is_seed_sequence<_Sseq, independent_bits_engine>::value &&
                           !is_convertible<_Sseq, _Engine>::value>::type* = 0)
         : __e_(__q) {}
    _LIBCPP_INLINE_VISIBILITY
    void seed() {__e_.seed();}
    _LIBCPP_INLINE_VISIBILITY
    void seed(result_type __sd) {__e_.seed(__sd);}
    template<class _Sseq>
        _LIBCPP_INLINE_VISIBILITY
        typename enable_if
        <
            __is_seed_sequence<_Sseq, independent_bits_engine>::value,
            void
        >::type
        seed(_Sseq& __q) {__e_.seed(__q);}

    // generating functions
    _LIBCPP_INLINE_VISIBILITY
    result_type operator()() {return __eval(integral_constant<bool, _Rp != 0>());}
    _LIBCPP_INLINE_VISIBILITY
    void discard(unsigned long long __z) {for (; __z; --__z) operator()();}

    // property functions
    _LIBCPP_INLINE_VISIBILITY
    const _Engine& base() const _NOEXCEPT {return __e_;}

    template<class _Eng, size_t _Wp, class _UInt>
    friend
    bool
    operator==(
        const independent_bits_engine<_Eng, _Wp, _UInt>& __x,
        const independent_bits_engine<_Eng, _Wp, _UInt>& __y);

    template<class _Eng, size_t _Wp, class _UInt>
    friend
    bool
    operator!=(
        const independent_bits_engine<_Eng, _Wp, _UInt>& __x,
        const independent_bits_engine<_Eng, _Wp, _UInt>& __y);

    template <class _CharT, class _Traits,
              class _Eng, size_t _Wp, class _UInt>
    friend
    basic_ostream<_CharT, _Traits>&
    operator<<(basic_ostream<_CharT, _Traits>& __os,
               const independent_bits_engine<_Eng, _Wp, _UInt>& __x);

    template <class _CharT, class _Traits,
              class _Eng, size_t _Wp, class _UInt>
    friend
    basic_istream<_CharT, _Traits>&
    operator>>(basic_istream<_CharT, _Traits>& __is,
               independent_bits_engine<_Eng, _Wp, _UInt>& __x);

private:
    _LIBCPP_INLINE_VISIBILITY
    result_type __eval(false_type);
    _LIBCPP_HIDE_FROM_ABI result_type __eval(true_type);

    template <size_t __count>
        _LIBCPP_INLINE_VISIBILITY
        static
        typename enable_if
        <
            __count < _Dt,
            result_type
        >::type
        __lshift(result_type __x) {return __x << __count;}

    template <size_t __count>
        _LIBCPP_INLINE_VISIBILITY
        static
        typename enable_if
        <
            (__count >= _Dt),
            result_type
        >::type
        __lshift(result_type) {return result_type(0);}
};

template<class _Engine, size_t __w, class _UIntType>
inline
_UIntType
independent_bits_engine<_Engine, __w, _UIntType>::__eval(false_type)
{
    return static_cast<result_type>(__e_() & __mask0);
}

template<class _Engine, size_t __w, class _UIntType>
_UIntType
independent_bits_engine<_Engine, __w, _UIntType>::__eval(true_type)
{
    result_type __sp = 0;
    for (size_t __k = 0; __k < __n0; ++__k)
    {
        _Engine_result_type __u;
        do
        {
            __u = __e_() - _Engine::min();
        } while (__u >= __y0);
        __sp = static_cast<result_type>(__lshift<__w0>(__sp) + (__u & __mask0));
    }
    for (size_t __k = __n0; __k < __n; ++__k)
    {
        _Engine_result_type __u;
        do
        {
            __u = __e_() - _Engine::min();
        } while (__u >= __y1);
        __sp = static_cast<result_type>(__lshift<__w0+1>(__sp) + (__u & __mask1));
    }
    return __sp;
}

template<class _Eng, size_t _Wp, class _UInt>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator==(
    const independent_bits_engine<_Eng, _Wp, _UInt>& __x,
    const independent_bits_engine<_Eng, _Wp, _UInt>& __y)
{
    return __x.base() == __y.base();
}

template<class _Eng, size_t _Wp, class _UInt>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator!=(
    const independent_bits_engine<_Eng, _Wp, _UInt>& __x,
    const independent_bits_engine<_Eng, _Wp, _UInt>& __y)
{
    return !(__x == __y);
}

template <class _CharT, class _Traits,
          class _Eng, size_t _Wp, class _UInt>
_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os,
           const independent_bits_engine<_Eng, _Wp, _UInt>& __x)
{
    return __os << __x.base();
}

template <class _CharT, class _Traits,
          class _Eng, size_t _Wp, class _UInt>
_LIBCPP_HIDE_FROM_ABI basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __is,
           independent_bits_engine<_Eng, _Wp, _UInt>& __x)
{
    _Eng __e;
    __is >> __e;
    if (!__is.fail())
        __x.__e_ = __e;
    return __is;
}

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___RANDOM_INDEPENDENT_BITS_ENGINE_H
