libcxx/include/__algorithm/ranges_partition_point.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_RANGES_PARTITION_POINT_H
  10 #define _LIBCPP___ALGORITHM_RANGES_PARTITION_POINT_H
  11
  12 #include <__algorithm/half_positive.h>
  13 #include <__config>
  14 #include <__functional/identity.h>
  15 #include <__functional/invoke.h>
  16 #include <__iterator/concepts.h>
  17 #include <__iterator/distance.h>
  18 #include <__iterator/iterator_traits.h>
  19 #include <__iterator/next.h>
  20 #include <__iterator/projected.h>
  21 #include <__ranges/access.h>
  22 #include <__ranges/concepts.h>
  23 #include <__ranges/dangling.h>
  24 #include <__utility/move.h>
  25
  26 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  27 #  pragma GCC system_header
  28 #endif
  29
  30 #if _LIBCPP_STD_VER >= 20
  31
  32 _LIBCPP_BEGIN_NAMESPACE_STD
  33
  34 namespace ranges {
  35 namespace __partition_point {
  36
  37 struct __fn {
  38   // TODO(ranges): delegate to the classic algorithm.
  39   template <class _Iter, class _Sent, class _Proj, class _Pred>
  40   _LIBCPP_HIDE_FROM_ABI constexpr static _Iter
  41   __partition_point_fn_impl(_Iter&& __first, _Sent&& __last, _Pred& __pred, _Proj& __proj) {
  42     auto __len = ranges::distance(__first, __last);
  43
  44     while (__len != 0) {
  45       auto __half_len = std::__half_positive(__len);
  46       auto __mid      = ranges::next(__first, __half_len);
  47
  48       if (std::invoke(__pred, std::invoke(__proj, *__mid))) {
  49         __first = ++__mid;
  50         __len -= __half_len + 1;
  51
  52       } else {
  53         __len = __half_len;
  54       }
  55     }
  56
  57     return __first;
  58   }
  59
  60   template <forward_iterator _Iter,
  61             sentinel_for<_Iter> _Sent,
  62             class _Proj = identity,
  63             indirect_unary_predicate<projected<_Iter, _Proj>> _Pred>
  64   _LIBCPP_HIDE_FROM_ABI constexpr _Iter operator()(_Iter __first, _Sent __last, _Pred __pred, _Proj __proj = {}) const {
  65     return __partition_point_fn_impl(std::move(__first), std::move(__last), __pred, __proj);
  66   }
  67
  68   template <forward_range _Range,
  69             class _Proj = identity,
  70             indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
  71   _LIBCPP_HIDE_FROM_ABI constexpr borrowed_iterator_t<_Range>
  72   operator()(_Range&& __range, _Pred __pred, _Proj __proj = {}) const {
  73     return __partition_point_fn_impl(ranges::begin(__range), ranges::end(__range), __pred, __proj);
  74   }
  75 };
  76
  77 } // namespace __partition_point
  78
  79 inline namespace __cpo {
  80 inline constexpr auto partition_point = __partition_point::__fn{};
  81 } // namespace __cpo
  82 } // namespace ranges
  83
  84 _LIBCPP_END_NAMESPACE_STD
  85
  86 #endif // _LIBCPP_STD_VER >= 20
  87
  88 #endif // _LIBCPP___ALGORITHM_RANGES_PARTITION_POINT_H