libcxx/include/__algorithm/copy_move_common.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_MOVE_COMMON_H
  10 #define _LIBCPP___ALGORITHM_COPY_MOVE_COMMON_H
  11
  12 #include <__algorithm/unwrap_iter.h>
  13 #include <__algorithm/unwrap_range.h>
  14 #include <__config>
  15 #include <__cstddef/size_t.h>
  16 #include <__iterator/iterator_traits.h>
  17 #include <__memory/pointer_traits.h>
  18 #include <__string/constexpr_c_functions.h>
  19 #include <__type_traits/enable_if.h>
  20 #include <__type_traits/is_always_bitcastable.h>
  21 #include <__type_traits/is_constant_evaluated.h>
  22 #include <__type_traits/is_constructible.h>
  23 #include <__type_traits/is_trivially_assignable.h>
  24 #include <__type_traits/is_volatile.h>
  25 #include <__utility/move.h>
  26 #include <__utility/pair.h>
  27
  28 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  29 #  pragma GCC system_header
  30 #endif
  31
  32 _LIBCPP_PUSH_MACROS
  33 #include <__undef_macros>
  34
  35 _LIBCPP_BEGIN_NAMESPACE_STD
  36
  37 // Type traits.
  38
  39 template <class _From, class _To>
  40 struct __can_lower_copy_assignment_to_memmove {
  41   static const bool value =
  42       // If the types are always bitcastable, it's valid to do a bitwise copy between them.
  43       __is_always_bitcastable<_From, _To>::value &&
  44       // Reject conversions that wouldn't be performed by the regular built-in assignment (e.g. between arrays).
  45       is_trivially_assignable<_To&, const _From&>::value &&
  46       // `memmove` doesn't accept `volatile` pointers, make sure the optimization SFINAEs away in that case.
  47       !is_volatile<_From>::value && !is_volatile<_To>::value;
  48 };
  49
  50 template <class _From, class _To>
  51 struct __can_lower_move_assignment_to_memmove {
  52   static const bool value =
  53       __is_always_bitcastable<_From, _To>::value && is_trivially_assignable<_To&, _From&&>::value &&
  54       !is_volatile<_From>::value && !is_volatile<_To>::value;
  55 };
  56
  57 // `memmove` algorithms implementation.
  58
  59 template <class _In, class _Out>
  60 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
  61 __copy_trivial_impl(_In* __first, _In* __last, _Out* __result) {
  62   const size_t __n = static_cast<size_t>(__last - __first);
  63
  64   std::__constexpr_memmove(__result, __first, __element_count(__n));
  65
  66   return std::make_pair(__last, __result + __n);
  67 }
  68
  69 template <class _In, class _Out>
  70 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
  71 __copy_backward_trivial_impl(_In* __first, _In* __last, _Out* __result) {
  72   const size_t __n = static_cast<size_t>(__last - __first);
  73   __result -= __n;
  74
  75   std::__constexpr_memmove(__result, __first, __element_count(__n));
  76
  77   return std::make_pair(__last, __result);
  78 }
  79
  80 // Iterator unwrapping and dispatching to the correct overload.
  81
  82 template <class _InIter, class _OutIter>
  83 struct __can_rewrap
  84     : integral_constant<bool, is_copy_constructible<_InIter>::value && is_copy_constructible<_OutIter>::value> {};
  85
  86 template <class _Algorithm,
  87           class _InIter,
  88           class _Sent,
  89           class _OutIter,
  90           __enable_if_t<__can_rewrap<_InIter, _OutIter>::value, int> = 0>
  91 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pair<_InIter, _OutIter>
  92 __copy_move_unwrap_iters(_InIter __first, _Sent __last, _OutIter __out_first) {
  93   auto __range  = std::__unwrap_range(__first, std::move(__last));
  94   auto __result = _Algorithm()(std::move(__range.first), std::move(__range.second), std::__unwrap_iter(__out_first));
  95   return std::make_pair(std::__rewrap_range<_Sent>(std::move(__first), std::move(__result.first)),
  96                         std::__rewrap_iter(std::move(__out_first), std::move(__result.second)));
  97 }
  98
  99 template <class _Algorithm,
 100           class _InIter,
 101           class _Sent,
 102           class _OutIter,
 103           __enable_if_t<!__can_rewrap<_InIter, _OutIter>::value, int> = 0>
 104 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pair<_InIter, _OutIter>
 105 __copy_move_unwrap_iters(_InIter __first, _Sent __last, _OutIter __out_first) {
 106   return _Algorithm()(std::move(__first), std::move(__last), std::move(__out_first));
 107 }
 108
 109 _LIBCPP_END_NAMESPACE_STD
 110
 111 _LIBCPP_POP_MACROS
 112
 113 #endif // _LIBCPP___ALGORITHM_COPY_MOVE_COMMON_H