libcxx/include/__algorithm/copy_backward.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___ALGORITHM_COPY_BACKWARD_H
  10 #define _LIBCPP___ALGORITHM_COPY_BACKWARD_H
  11
  12 #include <__algorithm/copy_move_common.h>
  13 #include <__algorithm/iterator_operations.h>
  14 #include <__algorithm/min.h>
  15 #include <__config>
  16 #include <__iterator/iterator_traits.h>
  17 #include <__iterator/segmented_iterator.h>
  18 #include <__type_traits/common_type.h>
  19 #include <__type_traits/enable_if.h>
  20 #include <__type_traits/is_constructible.h>
  21 #include <__utility/move.h>
  22 #include <__utility/pair.h>
  23
  24 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  25 #  pragma GCC system_header
  26 #endif
  27
  28 _LIBCPP_PUSH_MACROS
  29 #include <__undef_macros>
  30
  31 _LIBCPP_BEGIN_NAMESPACE_STD
  32
  33 template <class _AlgPolicy, class _InIter, class _Sent, class _OutIter>
  34 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InIter, _OutIter>
  35 __copy_backward(_InIter __first, _Sent __last, _OutIter __result);
  36
  37 template <class _AlgPolicy>
  38 struct __copy_backward_impl {
  39   template <class _InIter, class _Sent, class _OutIter>
  40   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
  41   operator()(_InIter __first, _Sent __last, _OutIter __result) const {
  42     auto __last_iter          = _IterOps<_AlgPolicy>::next(__first, __last);
  43     auto __original_last_iter = __last_iter;
  44
  45     while (__first != __last_iter) {
  46       *--__result = *--__last_iter;
  47     }
  48
  49     return std::make_pair(std::move(__original_last_iter), std::move(__result));
  50   }
  51
  52   template <class _InIter, class _OutIter, __enable_if_t<__is_segmented_iterator<_InIter>::value, int> = 0>
  53   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
  54   operator()(_InIter __first, _InIter __last, _OutIter __result) const {
  55     using _Traits = __segmented_iterator_traits<_InIter>;
  56     auto __sfirst = _Traits::__segment(__first);
  57     auto __slast  = _Traits::__segment(__last);
  58     if (__sfirst == __slast) {
  59       auto __iters =
  60           std::__copy_backward<_AlgPolicy>(_Traits::__local(__first), _Traits::__local(__last), std::move(__result));
  61       return std::make_pair(__last, __iters.second);
  62     }
  63
  64     __result =
  65         std::__copy_backward<_AlgPolicy>(_Traits::__begin(__slast), _Traits::__local(__last), std::move(__result))
  66             .second;
  67     --__slast;
  68     while (__sfirst != __slast) {
  69       __result =
  70           std::__copy_backward<_AlgPolicy>(_Traits::__begin(__slast), _Traits::__end(__slast), std::move(__result))
  71               .second;
  72       --__slast;
  73     }
  74     __result = std::__copy_backward<_AlgPolicy>(_Traits::__local(__first), _Traits::__end(__slast), std::move(__result))
  75                    .second;
  76     return std::make_pair(__last, std::move(__result));
  77   }
  78
  79   template <class _InIter,
  80             class _OutIter,
  81             __enable_if_t<__has_random_access_iterator_category<_InIter>::value &&
  82                               !__is_segmented_iterator<_InIter>::value && __is_segmented_iterator<_OutIter>::value,
  83                           int> = 0>
  84   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
  85   operator()(_InIter __first, _InIter __last, _OutIter __result) const {
  86     using _Traits           = __segmented_iterator_traits<_OutIter>;
  87     auto __orig_last        = __last;
  88     auto __segment_iterator = _Traits::__segment(__result);
  89
  90     // When the range contains no elements, __result might not be a valid iterator
  91     if (__first == __last)
  92       return std::make_pair(__first, __result);
  93
  94     auto __local_last = _Traits::__local(__result);
  95     while (true) {
  96       using _DiffT = typename common_type<__iter_diff_t<_InIter>, __iter_diff_t<_OutIter> >::type;
  97
  98       auto __local_first = _Traits::__begin(__segment_iterator);
  99       auto __size        = std::min<_DiffT>(__local_last - __local_first, __last - __first);
 100       auto __iter        = std::__copy_backward<_AlgPolicy>(__last - __size, __last, __local_last).second;
 101       __last -= __size;
 102
 103       if (__first == __last)
 104         return std::make_pair(std::move(__orig_last), _Traits::__compose(__segment_iterator, std::move(__iter)));
 105       --__segment_iterator;
 106       __local_last = _Traits::__end(__segment_iterator);
 107     }
 108   }
 109
 110   // At this point, the iterators have been unwrapped so any `contiguous_iterator` has been unwrapped to a pointer.
 111   template <class _In, class _Out, __enable_if_t<__can_lower_copy_assignment_to_memmove<_In, _Out>::value, int> = 0>
 112   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
 113   operator()(_In* __first, _In* __last, _Out* __result) const {
 114     return std::__copy_backward_trivial_impl(__first, __last, __result);
 115   }
 116 };
 117
 118 template <class _AlgPolicy, class _BidirectionalIterator1, class _Sentinel, class _BidirectionalIterator2>
 119 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_BidirectionalIterator1, _BidirectionalIterator2>
 120 __copy_backward(_BidirectionalIterator1 __first, _Sentinel __last, _BidirectionalIterator2 __result) {
 121   return std::__copy_move_unwrap_iters<__copy_backward_impl<_AlgPolicy> >(
 122       std::move(__first), std::move(__last), std::move(__result));
 123 }
 124
 125 template <class _BidirectionalIterator1, class _BidirectionalIterator2>
 126 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _BidirectionalIterator2
 127 copy_backward(_BidirectionalIterator1 __first, _BidirectionalIterator1 __last, _BidirectionalIterator2 __result) {
 128   static_assert(std::is_copy_constructible<_BidirectionalIterator1>::value &&
 129                     std::is_copy_constructible<_BidirectionalIterator1>::value,
 130                 "Iterators must be copy constructible.");
 131
 132   return std::__copy_backward<_ClassicAlgPolicy>(std::move(__first), std::move(__last), std::move(__result)).second;
 133 }
 134
 135 _LIBCPP_END_NAMESPACE_STD
 136
 137 _LIBCPP_POP_MACROS
 138
 139 #endif // _LIBCPP___ALGORITHM_COPY_BACKWARD_H