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_FIND_SEGMENT_IF_H 10 #define _LIBCPP___ALGORITHM_FIND_SEGMENT_IF_H 11 12 #include <__config> 13 #include <__iterator/segmented_iterator.h> 14 15 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 16 # pragma GCC system_header 17 #endif 18 19 _LIBCPP_BEGIN_NAMESPACE_STD 20 21 // __find_segment_if is a utility function for optimizing iteration over segmented iterators linearly. 22 // [__first, __last) has to be a segmented range. __pred is expected to take a range of local iterators and the __proj. 23 // It returns an iterator to the first element that satisfies the predicate, or a one-past-the-end iterator if there was 24 // no match. __proj may be anything that should be passed to __pred, but is expected to be a projection to support 25 // ranges algorithms, or __identity for classic algorithms. 26 27 template <class _SegmentedIterator, class _Pred, class _Proj> 28 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _SegmentedIterator 29 __find_segment_if(_SegmentedIterator __first, _SegmentedIterator __last, _Pred __pred, _Proj& __proj) { 30 using _Traits = __segmented_iterator_traits<_SegmentedIterator>; 31 32 auto __sfirst = _Traits::__segment(__first); 33 auto __slast = _Traits::__segment(__last); 34 35 // We are in a single segment, so we might not be at the beginning or end 36 if (__sfirst == __slast) 37 return _Traits::__compose(__sfirst, __pred(_Traits::__local(__first), _Traits::__local(__last), __proj)); 38 39 { // We have more than one segment. Iterate over the first segment, since we might not start at the beginning 40 auto __llast = _Traits::__end(__sfirst); 41 auto __liter = __pred(_Traits::__local(__first), __llast, __proj); 42 if (__liter != __llast) 43 return _Traits::__compose(__sfirst, __liter); 44 } 45 ++__sfirst; 46 47 // Iterate over the segments which are guaranteed to be completely in the range 48 while (__sfirst != __slast) { 49 auto __llast = _Traits::__end(__sfirst); 50 auto __liter = __pred(_Traits::__begin(__sfirst), _Traits::__end(__sfirst), __proj); 51 if (__liter != __llast) 52 return _Traits::__compose(__sfirst, __liter); 53 ++__sfirst; 54 } 55 56 // Iterate over the last segment 57 return _Traits::__compose(__sfirst, __pred(_Traits::__begin(__sfirst), _Traits::__local(__last), __proj)); 58 } 59 60 _LIBCPP_END_NAMESPACE_STD 61 62 #endif // _LIBCPP___ALGORITHM_FIND_SEGMENT_IF_H 63