ranges_algobase.h

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// Core algorithmic facilities -*- C++ -*-
 
// Copyright (C) 2020-2025 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
 
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
 
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
 
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.
 
/** @file bits/ranges_algobase.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{algorithm}
 */
 
#ifndef _RANGES_ALGOBASE_H
#define _RANGES_ALGOBASE_H 1
 
#if __cplusplus > 201703L
 
#include <compare>
#include <bits/stl_iterator_base_funcs.h>
#include <bits/stl_iterator.h>
#include <bits/ranges_base.h> // ranges::begin, ranges::range etc.
#include <bits/invoke.h>      // __invoke
#include <bits/cpp_type_traits.h> // __is_byte
#include <bits/stl_algobase.h> // __memcmp
 
#if __cpp_lib_concepts
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace ranges
{
  namespace __detail
  {
    template<typename _Tp>
      constexpr inline bool __is_normal_iterator = false;
 
    template<typename _Iterator, typename _Container>
      constexpr inline bool
        __is_normal_iterator<__gnu_cxx::__normal_iterator<_Iterator,
                                                          _Container>> = true;
 
    template<typename _Tp>
      constexpr inline bool __is_reverse_iterator = false;
 
    template<typename _Iterator>
      constexpr inline bool
        __is_reverse_iterator<reverse_iterator<_Iterator>> = true;
 
    template<typename _Tp>
      constexpr inline bool __is_move_iterator = false;
 
    template<typename _Iterator>
      constexpr inline bool
        __is_move_iterator<move_iterator<_Iterator>> = true;
  } // namespace __detail
 
#if __glibcxx_ranges_iota >= 202202L // C++ >= 23
  template<typename _Out, typename _Tp>
    struct out_value_result
    {
      [[no_unique_address]] _Out out;
      [[no_unique_address]] _Tp value;
 
      template<typename _Out2, typename _Tp2>
        requires convertible_to<const _Out&, _Out2>
          && convertible_to<const _Tp&, _Tp2>
        constexpr
        operator out_value_result<_Out2, _Tp2>() const &
        { return {out, value}; }
 
      template<typename _Out2, typename _Tp2>
        requires convertible_to<_Out, _Out2>
          && convertible_to<_Tp, _Tp2>
        constexpr
        operator out_value_result<_Out2, _Tp2>() &&
        { return {std::move(out), std::move(value)}; }
    };
#endif // __glibcxx_ranges_iota
 
  struct __equal_fn
  {
    template<input_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
             input_iterator _Iter2, sentinel_for<_Iter2> _Sent2,
             typename _Pred = ranges::equal_to,
             typename _Proj1 = identity, typename _Proj2 = identity>
      requires indirectly_comparable<_Iter1, _Iter2, _Pred, _Proj1, _Proj2>
      [[nodiscard]] constexpr bool
      operator()(_Iter1 __first1, _Sent1 __last1,
                 _Iter2 __first2, _Sent2 __last2, _Pred __pred = {},
                 _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
      {
        // TODO: implement more specializations to at least have parity with
        // std::equal.
        if constexpr (__detail::__is_normal_iterator<_Iter1>
                      && same_as<_Iter1, _Sent1>)
          return (*this)(__first1.base(), __last1.base(),
                         std::move(__first2), std::move(__last2),
                         std::move(__pred),
                         std::move(__proj1), std::move(__proj2));
        else if constexpr (__detail::__is_normal_iterator<_Iter2>
                           && same_as<_Iter2, _Sent2>)
          return (*this)(std::move(__first1), std::move(__last1),
                         __first2.base(), __last2.base(),
                         std::move(__pred),
                         std::move(__proj1), std::move(__proj2));
        else if constexpr (sized_sentinel_for<_Sent1, _Iter1>
                           && sized_sentinel_for<_Sent2, _Iter2>)
          {
            auto __d1 = ranges::distance(__first1, __last1);
            auto __d2 = ranges::distance(__first2, __last2);
            if (__d1 != __d2)
              return false;
 
            using _ValueType1 = iter_value_t<_Iter1>;
            constexpr bool __use_memcmp
              = ((is_integral_v<_ValueType1> || is_pointer_v<_ValueType1>)
                 && __memcmpable<_Iter1, _Iter2>::__value
                 && is_same_v<_Pred, ranges::equal_to>
                 && is_same_v<_Proj1, identity>
                 && is_same_v<_Proj2, identity>);
            if constexpr (__use_memcmp)
              {
                if (const size_t __len = (__last1 - __first1))
                  return !std::__memcmp(__first1, __first2, __len);
                return true;
              }
            else
              {
                for (; __first1 != __last1; ++__first1, (void)++__first2)
                  if (!(bool)std::__invoke(__pred,
                                           std::__invoke(__proj1, *__first1),
                                           std::__invoke(__proj2, *__first2)))
                    return false;
                return true;
              }
          }
        else
          {
            for (; __first1 != __last1 && __first2 != __last2;
                 ++__first1, (void)++__first2)
              if (!(bool)std::__invoke(__pred,
                                       std::__invoke(__proj1, *__first1),
                                       std::__invoke(__proj2, *__first2)))
                return false;
            return __first1 == __last1 && __first2 == __last2;
          }
      }
 
    template<input_range _Range1, input_range _Range2,
             typename _Pred = ranges::equal_to,
             typename _Proj1 = identity, typename _Proj2 = identity>
      requires indirectly_comparable<iterator_t<_Range1>, iterator_t<_Range2>,
                                     _Pred, _Proj1, _Proj2>
      [[nodiscard]] constexpr bool
      operator()(_Range1&& __r1, _Range2&& __r2, _Pred __pred = {},
                 _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
      {
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // 3560. ranges::equal [...] should short-circuit for sized_ranges
        if constexpr (sized_range<_Range1>)
          if constexpr (sized_range<_Range2>)
            if (ranges::distance(__r1) != ranges::distance(__r2))
              return false;
 
        return (*this)(ranges::begin(__r1), ranges::end(__r1),
                       ranges::begin(__r2), ranges::end(__r2),
                       std::move(__pred),
                       std::move(__proj1), std::move(__proj2));
      }
  };
 
  inline constexpr __equal_fn equal{};
 
namespace __detail
{
  template<bool _IsMove, typename _OutIter, typename _InIter>
    [[__gnu__::__always_inline__]]
    constexpr void
    __assign_one(_OutIter& __out, _InIter& __in)
    {
      if constexpr (_IsMove)
        *__out = ranges::iter_move(__in);
      else
        *__out = *__in;
    }
} // namespace __detail
 
  template<typename _Iter, typename _Out>
    struct in_out_result
    {
      [[no_unique_address]] _Iter in;
      [[no_unique_address]] _Out out;
 
      template<typename _Iter2, typename _Out2>
        requires convertible_to<const _Iter&, _Iter2>
          && convertible_to<const _Out&, _Out2>
        constexpr
        operator in_out_result<_Iter2, _Out2>() const &
        { return {in, out}; }
 
      template<typename _Iter2, typename _Out2>
        requires convertible_to<_Iter, _Iter2>
          && convertible_to<_Out, _Out2>
        constexpr
        operator in_out_result<_Iter2, _Out2>() &&
        { return {std::move(in), std::move(out)}; }
    };
 
  template<typename _Iter, typename _Out>
    using copy_result = in_out_result<_Iter, _Out>;
 
  template<typename _Iter, typename _Out>
    using move_result = in_out_result<_Iter, _Out>;
 
  template<typename _Iter1, typename _Iter2>
    using move_backward_result = in_out_result<_Iter1, _Iter2>;
 
  template<typename _Iter1, typename _Iter2>
    using copy_backward_result = in_out_result<_Iter1, _Iter2>;
 
  template<bool _IsMove,
           bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent,
           bidirectional_iterator _Out>
    requires (_IsMove
              ? indirectly_movable<_Iter, _Out>
              : indirectly_copyable<_Iter, _Out>)
    constexpr __conditional_t<_IsMove,
                              move_backward_result<_Iter, _Out>,
                              copy_backward_result<_Iter, _Out>>
    __copy_or_move_backward(_Iter __first, _Sent __last, _Out __result);
 
  template<bool _IsMove,
           input_iterator _Iter, sentinel_for<_Iter> _Sent,
           weakly_incrementable _Out>
    requires (_IsMove
              ? indirectly_movable<_Iter, _Out>
              : indirectly_copyable<_Iter, _Out>)
    constexpr __conditional_t<_IsMove,
                              move_result<_Iter, _Out>,
                              copy_result<_Iter, _Out>>
    __copy_or_move(_Iter __first, _Sent __last, _Out __result)
    {
      // TODO: implement more specializations to be at least on par with
      // std::copy/std::move.
      using __detail::__is_move_iterator;
      using __detail::__is_reverse_iterator;
      using __detail::__is_normal_iterator;
      if constexpr (__is_move_iterator<_Iter> && same_as<_Iter, _Sent>)
        {
          auto [__in, __out]
            = ranges::__copy_or_move<true>(std::move(__first).base(),
                                           std::move(__last).base(),
                                           std::move(__result));
          return {move_iterator{std::move(__in)}, std::move(__out)};
        }
      else if constexpr (__is_reverse_iterator<_Iter> && same_as<_Iter, _Sent>
                         && __is_reverse_iterator<_Out>)
        {
          auto [__in,__out]
            = ranges::__copy_or_move_backward<_IsMove>(std::move(__last).base(),
                                                       std::move(__first).base(),
                                                       std::move(__result).base());
          return {reverse_iterator{std::move(__in)},
                  reverse_iterator{std::move(__out)}};
        }
      else if constexpr (__is_normal_iterator<_Iter> && same_as<_Iter, _Sent>)
        {
          auto [__in,__out]
            = ranges::__copy_or_move<_IsMove>(__first.base(), __last.base(),
                                              std::move(__result));
          return {decltype(__first){__in}, std::move(__out)};
        }
      else if constexpr (__is_normal_iterator<_Out>)
        {
          auto [__in,__out]
            = ranges::__copy_or_move<_IsMove>(std::move(__first), __last, __result.base());
          return {std::move(__in), decltype(__result){__out}};
        }
      else if constexpr (sized_sentinel_for<_Sent, _Iter>)
        {
          if (!std::__is_constant_evaluated())
            {
              if constexpr (__memcpyable<_Out, _Iter>::__value)
                {
                  using _ValueTypeI = iter_value_t<_Iter>;
                  auto __num = __last - __first;
                  if (__num > 1) [[likely]]
                    __builtin_memmove(__result, __first,
                                      sizeof(_ValueTypeI) * __num);
                  else if (__num == 1)
                    __detail::__assign_one<_IsMove>(__result, __first);
                  return {__first + __num, __result + __num};
                }
            }
 
          for (auto __n = __last - __first; __n > 0; --__n)
            {
              __detail::__assign_one<_IsMove>(__result, __first);
              ++__first;
              ++__result;
            }
          return {std::move(__first), std::move(__result)};
        }
      else
        {
          while (__first != __last)
            {
              __detail::__assign_one<_IsMove>(__result, __first);
              ++__first;
              ++__result;
            }
          return {std::move(__first), std::move(__result)};
        }
    }
 
  struct __copy_fn
  {
    template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
             weakly_incrementable _Out>
      requires indirectly_copyable<_Iter, _Out>
      constexpr copy_result<_Iter, _Out>
      operator()(_Iter __first, _Sent __last, _Out __result) const
      {
        return ranges::__copy_or_move<false>(std::move(__first),
                                             std::move(__last),
                                             std::move(__result));
      }
 
    template<input_range _Range, weakly_incrementable _Out>
      requires indirectly_copyable<iterator_t<_Range>, _Out>
      constexpr copy_result<borrowed_iterator_t<_Range>, _Out>
      operator()(_Range&& __r, _Out __result) const
      {
        return (*this)(ranges::begin(__r), ranges::end(__r),
                       std::move(__result));
      }
  };
 
  inline constexpr __copy_fn copy{};
 
  struct __move_fn
  {
    template<input_iterator _Iter, sentinel_for<_Iter> _Sent,
             weakly_incrementable _Out>
      requires indirectly_movable<_Iter, _Out>
      constexpr move_result<_Iter, _Out>
      operator()(_Iter __first, _Sent __last, _Out __result) const
      {
        return ranges::__copy_or_move<true>(std::move(__first),
                                            std::move(__last),
                                            std::move(__result));
      }
 
    template<input_range _Range, weakly_incrementable _Out>
      requires indirectly_movable<iterator_t<_Range>, _Out>
      constexpr move_result<borrowed_iterator_t<_Range>, _Out>
      operator()(_Range&& __r, _Out __result) const
      {
        return (*this)(ranges::begin(__r), ranges::end(__r),
                       std::move(__result));
      }
  };
 
  inline constexpr __move_fn move{};
 
  template<bool _IsMove,
           bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent,
           bidirectional_iterator _Out>
    requires (_IsMove
              ? indirectly_movable<_Iter, _Out>
              : indirectly_copyable<_Iter, _Out>)
    constexpr __conditional_t<_IsMove,
                              move_backward_result<_Iter, _Out>,
                              copy_backward_result<_Iter, _Out>>
    __copy_or_move_backward(_Iter __first, _Sent __last, _Out __result)
    {
      // TODO: implement more specializations to be at least on par with
      // std::copy_backward/std::move_backward.
      using __detail::__is_reverse_iterator;
      using __detail::__is_normal_iterator;
      if constexpr (__is_reverse_iterator<_Iter> && same_as<_Iter, _Sent>
                    && __is_reverse_iterator<_Out>)
        {
          auto [__in,__out]
            = ranges::__copy_or_move<_IsMove>(std::move(__last).base(),
                                              std::move(__first).base(),
                                              std::move(__result).base());
          return {reverse_iterator{std::move(__in)},
                  reverse_iterator{std::move(__out)}};
        }
      else if constexpr (__is_normal_iterator<_Iter> && same_as<_Iter, _Sent>)
        {
          auto [__in,__out]
            = ranges::__copy_or_move_backward<_IsMove>(__first.base(),
                                                       __last.base(),
                                                       std::move(__result));
          return {decltype(__first){__in}, std::move(__out)};
        }
      else if constexpr (__is_normal_iterator<_Out>)
        {
          auto [__in,__out]
            = ranges::__copy_or_move_backward<_IsMove>(std::move(__first),
                                                       std::move(__last),
                                                       __result.base());
          return {std::move(__in), decltype(__result){__out}};
        }
      else if constexpr (sized_sentinel_for<_Sent, _Iter>)
        {
          if (!std::__is_constant_evaluated())
            {
              if constexpr (__memcpyable<_Out, _Iter>::__value)
                {
                  using _ValueTypeI = iter_value_t<_Iter>;
                  auto __num = __last - __first;
                  __result -= __num;
                  if (__num > 1) [[likely]]
                    __builtin_memmove(__result, __first,
                                      sizeof(_ValueTypeI) * __num);
                  else if (__num == 1)
                    __detail::__assign_one<_IsMove>(__result, __first);
                  return {__first + __num, __result};
                }
            }
 
          auto __lasti = ranges::next(__first, __last);
          auto __tail = __lasti;
 
          for (auto __n = __last - __first; __n > 0; --__n)
            {
              --__tail;
              --__result;
              __detail::__assign_one<_IsMove>(__result, __tail);
            }
          return {std::move(__lasti), std::move(__result)};
        }
      else
        {
          auto __lasti = ranges::next(__first, __last);
          auto __tail = __lasti;
 
          while (__first != __tail)
            {
              --__tail;
              --__result;
              __detail::__assign_one<_IsMove>(__result, __tail);
            }
          return {std::move(__lasti), std::move(__result)};
        }
    }
 
  struct __copy_backward_fn
  {
    template<bidirectional_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
             bidirectional_iterator _Iter2>
      requires indirectly_copyable<_Iter1, _Iter2>
      constexpr copy_backward_result<_Iter1, _Iter2>
      operator()(_Iter1 __first, _Sent1 __last, _Iter2 __result) const
      {
        return ranges::__copy_or_move_backward<false>(std::move(__first),
                                                      std::move(__last),
                                                      std::move(__result));
      }
 
    template<bidirectional_range _Range, bidirectional_iterator _Iter>
      requires indirectly_copyable<iterator_t<_Range>, _Iter>
      constexpr copy_backward_result<borrowed_iterator_t<_Range>, _Iter>
      operator()(_Range&& __r, _Iter __result) const
      {
        return (*this)(ranges::begin(__r), ranges::end(__r),
                       std::move(__result));
      }
  };
 
  inline constexpr __copy_backward_fn copy_backward{};
 
  struct __move_backward_fn
  {
    template<bidirectional_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
             bidirectional_iterator _Iter2>
      requires indirectly_movable<_Iter1, _Iter2>
      constexpr move_backward_result<_Iter1, _Iter2>
      operator()(_Iter1 __first, _Sent1 __last, _Iter2 __result) const
      {
        return ranges::__copy_or_move_backward<true>(std::move(__first),
                                                     std::move(__last),
                                                     std::move(__result));
      }
 
    template<bidirectional_range _Range, bidirectional_iterator _Iter>
      requires indirectly_movable<iterator_t<_Range>, _Iter>
      constexpr move_backward_result<borrowed_iterator_t<_Range>, _Iter>
      operator()(_Range&& __r, _Iter __result) const
      {
        return (*this)(ranges::begin(__r), ranges::end(__r),
                       std::move(__result));
      }
  };
 
  inline constexpr __move_backward_fn move_backward{};
 
  template<typename _Iter, typename _Out>
    using copy_n_result = in_out_result<_Iter, _Out>;
 
  struct __copy_n_fn
  {
    template<input_iterator _Iter, weakly_incrementable _Out>
      requires indirectly_copyable<_Iter, _Out>
      constexpr copy_n_result<_Iter, _Out>
      operator()(_Iter __first, iter_difference_t<_Iter> __n,
                 _Out __result) const
      {
        if constexpr (random_access_iterator<_Iter>)
          {
            if (__n > 0)
              return ranges::copy(__first, __first + __n, std::move(__result));
          }
        else
          {
            for (; __n > 0; --__n, (void)++__result, (void)++__first)
              *__result = *__first;
          }
        return {std::move(__first), std::move(__result)};
      }
  };
 
  inline constexpr __copy_n_fn copy_n{};
 
  struct __fill_n_fn
  {
    template<typename _Out,
             typename _Tp _GLIBCXX26_DEF_VAL_T(iter_value_t<_Out>)>
      requires output_iterator<_Out, const _Tp&>
      constexpr _Out
      operator()(_Out __first, iter_difference_t<_Out> __n,
                 const _Tp& __value) const
      {
        // TODO: implement more specializations to be at least on par with
        // std::fill_n
        if (__n <= 0)
          return __first;
 
        if constexpr (is_scalar_v<_Tp>)
          {
            // TODO: Generalize this optimization to contiguous iterators.
            if constexpr (is_pointer_v<_Out>
                          // Note that __is_byte already implies !is_volatile.
                          && __is_byte<remove_pointer_t<_Out>>::__value
                          && integral<_Tp>)
              {
                if (!std::__is_constant_evaluated())
                  {
                    __builtin_memset(__first,
                                     static_cast<unsigned char>(__value),
                                     __n);
                    return __first + __n;
                  }
              }
 
            const auto __tmp = __value;
            for (; __n > 0; --__n, (void)++__first)
              *__first = __tmp;
            return __first;
          }
        else
          {
            for (; __n > 0; --__n, (void)++__first)
              *__first = __value;
            return __first;
          }
      }
  };
 
  inline constexpr __fill_n_fn fill_n{};
 
  struct __fill_fn
  {
    template<typename _Out,
             sentinel_for<_Out> _Sent,
             typename _Tp _GLIBCXX26_DEF_VAL_T(iter_value_t<_Out>)>
      requires output_iterator<_Out, const _Tp&>
      constexpr _Out
      operator()(_Out __first, _Sent __last, const _Tp& __value) const
      {
        // TODO: implement more specializations to be at least on par with
        // std::fill
        if constexpr (sized_sentinel_for<_Sent, _Out>)
          {
            const auto __len = __last - __first;
            return ranges::fill_n(std::move(__first), __len, __value);
          }
        else if constexpr (is_scalar_v<_Tp>)
          {
            const auto __tmp = __value;
            for (; __first != __last; ++__first)
              *__first = __tmp;
            return __first;
          }
        else
          {
            for (; __first != __last; ++__first)
              *__first = __value;
            return __first;
          }
      }
 
    template<typename _Range,
             typename _Tp _GLIBCXX26_DEF_VAL_T(range_value_t<_Range>)>
      requires output_range<_Range, const _Tp&>
      constexpr borrowed_iterator_t<_Range>
      operator()(_Range&& __r, const _Tp& __value) const
      {
        return (*this)(ranges::begin(__r), ranges::end(__r), __value);
      }
  };
 
  inline constexpr __fill_fn fill{};
}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // concepts
#endif // C++20
#endif // _RANGES_ALGOBASE_H