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
89