llvm-project/libcxx/include/__algorithm/inplace_merge.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___ALGORITHM_INPLACE_MERGE_H
#define _LIBCPP___ALGORITHM_INPLACE_MERGE_H

#include <__config>
#include <__algorithm/comp_ref_type.h>
#include <__algorithm/comp.h>
#include <__algorithm/lower_bound.h>
#include <__algorithm/min.h>
#include <__algorithm/move.h>
#include <__algorithm/rotate.h>
#include <__algorithm/upper_bound.h>
#include <__iterator/iterator_traits.h>
#include <__utility/swap.h>
#include <memory>

#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 _Predicate>
class __invert // invert the sense of a comparison
{
private:
    _Predicate __p_;
public:
    _LIBCPP_INLINE_VISIBILITY __invert() {}

    _LIBCPP_INLINE_VISIBILITY
    explicit __invert(_Predicate __p) : __p_(__p) {}

    template <class _T1>
    _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _T1& __x) {return !__p_(__x);}

    template <class _T1, class _T2>
    _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _T1& __x, const _T2& __y) {return __p_(__y, __x);}
};

template <class _Compare, class _InputIterator1, class _InputIterator2,
          class _OutputIterator>
void __half_inplace_merge(_InputIterator1 __first1, _InputIterator1 __last1,
                          _InputIterator2 __first2, _InputIterator2 __last2,
                          _OutputIterator __result, _Compare __comp)
{
    for (; __first1 != __last1; ++__result)
    {
        if (__first2 == __last2)
        {
            _VSTD::move(__first1, __last1, __result);
            return;
        }

        if (__comp(*__first2, *__first1))
        {
            *__result = _VSTD::move(*__first2);
            ++__first2;
        }
        else
        {
            *__result = _VSTD::move(*__first1);
            ++__first1;
        }
    }
    // __first2 through __last2 are already in the right spot.
}

template <class _Compare, class _BidirectionalIterator>
void
__buffered_inplace_merge(_BidirectionalIterator __first, _BidirectionalIterator __middle, _BidirectionalIterator __last,
                _Compare __comp, typename iterator_traits<_BidirectionalIterator>::difference_type __len1,
                                 typename iterator_traits<_BidirectionalIterator>::difference_type __len2,
                typename iterator_traits<_BidirectionalIterator>::value_type* __buff)
{
    typedef typename iterator_traits<_BidirectionalIterator>::value_type value_type;
    __destruct_n __d(0);
    unique_ptr<value_type, __destruct_n&> __h2(__buff, __d);
    if (__len1 <= __len2)
    {
        value_type* __p = __buff;
        for (_BidirectionalIterator __i = __first; __i != __middle; __d.template __incr<value_type>(), (void) ++__i, (void) ++__p)
            ::new ((void*)__p) value_type(_VSTD::move(*__i));
        _VSTD::__half_inplace_merge<_Compare>(__buff, __p, __middle, __last, __first, __comp);
    }
    else
    {
        value_type* __p = __buff;
        for (_BidirectionalIterator __i = __middle; __i != __last; __d.template __incr<value_type>(), (void) ++__i, (void) ++__p)
            ::new ((void*)__p) value_type(_VSTD::move(*__i));
        typedef reverse_iterator<_BidirectionalIterator> _RBi;
        typedef reverse_iterator<value_type*> _Rv;
        typedef __invert<_Compare> _Inverted;
        _VSTD::__half_inplace_merge<_Inverted>(_Rv(__p), _Rv(__buff),
                                    _RBi(__middle), _RBi(__first),
                                    _RBi(__last), _Inverted(__comp));
    }
}

template <class _Compare, class _BidirectionalIterator>
void
__inplace_merge(_BidirectionalIterator __first, _BidirectionalIterator __middle, _BidirectionalIterator __last,
                _Compare __comp, typename iterator_traits<_BidirectionalIterator>::difference_type __len1,
                                 typename iterator_traits<_BidirectionalIterator>::difference_type __len2,
                typename iterator_traits<_BidirectionalIterator>::value_type* __buff, ptrdiff_t __buff_size)
{
    typedef typename iterator_traits<_BidirectionalIterator>::difference_type difference_type;
    while (true)
    {
        // if __middle == __last, we're done
        if (__len2 == 0)
            return;
        if (__len1 <= __buff_size || __len2 <= __buff_size)
            return _VSTD::__buffered_inplace_merge<_Compare>
                   (__first, __middle, __last, __comp, __len1, __len2, __buff);
        // shrink [__first, __middle) as much as possible (with no moves), returning if it shrinks to 0
        for (; true; ++__first, (void) --__len1)
        {
            if (__len1 == 0)
                return;
            if (__comp(*__middle, *__first))
                break;
        }
        // __first < __middle < __last
        // *__first > *__middle
        // partition [__first, __m1) [__m1, __middle) [__middle, __m2) [__m2, __last) such that
        //     all elements in:
        //         [__first, __m1)  <= [__middle, __m2)
        //         [__middle, __m2) <  [__m1, __middle)
        //         [__m1, __middle) <= [__m2, __last)
        //     and __m1 or __m2 is in the middle of its range
        _BidirectionalIterator __m1;  // "median" of [__first, __middle)
        _BidirectionalIterator __m2;  // "median" of [__middle, __last)
        difference_type __len11;      // distance(__first, __m1)
        difference_type __len21;      // distance(__middle, __m2)
        // binary search smaller range
        if (__len1 < __len2)
        {   // __len >= 1, __len2 >= 2
            __len21 = __len2 / 2;
            __m2 = __middle;
            _VSTD::advance(__m2, __len21);
            __m1 = _VSTD::__upper_bound<_Compare>(__first, __middle, *__m2, __comp);
            __len11 = _VSTD::distance(__first, __m1);
        }
        else
        {
            if (__len1 == 1)
            {   // __len1 >= __len2 && __len2 > 0, therefore __len2 == 1
                // It is known *__first > *__middle
                swap(*__first, *__middle);
                return;
            }
            // __len1 >= 2, __len2 >= 1
            __len11 = __len1 / 2;
            __m1 = __first;
            _VSTD::advance(__m1, __len11);
            __m2 = _VSTD::__lower_bound<_Compare>(__middle, __last, *__m1, __comp);
            __len21 = _VSTD::distance(__middle, __m2);
        }
        difference_type __len12 = __len1 - __len11;  // distance(__m1, __middle)
        difference_type __len22 = __len2 - __len21;  // distance(__m2, __last)
        // [__first, __m1) [__m1, __middle) [__middle, __m2) [__m2, __last)
        // swap middle two partitions
        __middle = _VSTD::rotate(__m1, __middle, __m2);
        // __len12 and __len21 now have swapped meanings
        // merge smaller range with recursive call and larger with tail recursion elimination
        if (__len11 + __len21 < __len12 + __len22)
        {
            _VSTD::__inplace_merge<_Compare>(__first, __m1, __middle, __comp, __len11, __len21, __buff, __buff_size);
//          _VSTD::__inplace_merge<_Compare>(__middle, __m2, __last, __comp, __len12, __len22, __buff, __buff_size);
            __first = __middle;
            __middle = __m2;
            __len1 = __len12;
            __len2 = __len22;
        }
        else
        {
            _VSTD::__inplace_merge<_Compare>(__middle, __m2, __last, __comp, __len12, __len22, __buff, __buff_size);
//          _VSTD::__inplace_merge<_Compare>(__first, __m1, __middle, __comp, __len11, __len21, __buff, __buff_size);
            __last = __middle;
            __middle = __m1;
            __len1 = __len11;
            __len2 = __len21;
        }
    }
}

template <class _BidirectionalIterator, class _Compare>
inline _LIBCPP_INLINE_VISIBILITY
void
inplace_merge(_BidirectionalIterator __first, _BidirectionalIterator __middle, _BidirectionalIterator __last,
              _Compare __comp)
{
    typedef typename iterator_traits<_BidirectionalIterator>::value_type value_type;
    typedef typename iterator_traits<_BidirectionalIterator>::difference_type difference_type;
    difference_type __len1 = _VSTD::distance(__first, __middle);
    difference_type __len2 = _VSTD::distance(__middle, __last);
    difference_type __buf_size = _VSTD::min(__len1, __len2);
    pair<value_type*, ptrdiff_t> __buf = _VSTD::get_temporary_buffer<value_type>(__buf_size);
    unique_ptr<value_type, __return_temporary_buffer> __h(__buf.first);
    typedef typename __comp_ref_type<_Compare>::type _Comp_ref;
    return _VSTD::__inplace_merge<_Comp_ref>(__first, __middle, __last, __comp, __len1, __len2,
                                            __buf.first, __buf.second);
}

template <class _BidirectionalIterator>
inline _LIBCPP_INLINE_VISIBILITY
void
inplace_merge(_BidirectionalIterator __first, _BidirectionalIterator __middle, _BidirectionalIterator __last)
{
    _VSTD::inplace_merge(__first, __middle, __last,
                        __less<typename iterator_traits<_BidirectionalIterator>::value_type>());
}

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___ALGORITHM_INPLACE_MERGE_H