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_FOR_EACH_N_SEGMENT_H
10 #define _LIBCPP___ALGORITHM_FOR_EACH_N_SEGMENT_H
11
12 #include <__config>
13 #include <__iterator/iterator_traits.h>
14 #include <__iterator/segmented_iterator.h>
15
16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
17 # pragma GCC system_header
18 #endif
19
20 _LIBCPP_BEGIN_NAMESPACE_STD
21
22 // __for_each_n_segment optimizes linear iteration over segmented iterators. It processes a segmented
23 // input range [__first, __first + __n) by applying the functor __func to each element within the segment.
24 // The return value of __func is ignored, and the function returns an iterator pointing to one past the
25 // last processed element in the input range.
26
27 template <class _SegmentedIterator, class _Size, class _Functor>
28 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _SegmentedIterator
__for_each_n_segment(_SegmentedIterator __first,_Size __orig_n,_Functor __func)29 __for_each_n_segment(_SegmentedIterator __first, _Size __orig_n, _Functor __func) {
30 static_assert(__is_segmented_iterator<_SegmentedIterator>::value &&
31 __has_random_access_iterator_category<
32 typename __segmented_iterator_traits<_SegmentedIterator>::__local_iterator>::value,
33 "__for_each_n_segment only works with segmented iterators with random-access local iterators");
34 if (__orig_n <= 0)
35 return __first;
36
37 using _Traits = __segmented_iterator_traits<_SegmentedIterator>;
38 using __local_iter_t = typename _Traits::__local_iterator;
39 using __difference_t = typename std::iterator_traits<__local_iter_t>::difference_type;
40 __difference_t __n = __orig_n;
41 auto __seg = _Traits::__segment(__first);
42 auto __local_first = _Traits::__local(__first);
43 __local_iter_t __local_last;
44
45 while (__n > 0) {
46 __local_last = _Traits::__end(__seg);
47 auto __seg_size = __local_last - __local_first;
48 if (__n <= __seg_size) {
49 __local_last = __local_first + __n;
50 __func(__local_first, __local_last);
51 break;
52 }
53 __func(__local_first, __local_last);
54 __n -= __seg_size;
55 __local_first = _Traits::__begin(++__seg);
56 }
57
58 return _Traits::__compose(__seg, __local_last);
59 }
60
61 _LIBCPP_END_NAMESPACE_STD
62
63 #endif // _LIBCPP___ALGORITHM_FOR_EACH_N_SEGMENT_H
64