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_SHIFT_LEFT_H 10 #define _LIBCPP___ALGORITHM_SHIFT_LEFT_H 11 12 #include <__algorithm/move.h> 13 #include <__config> 14 #include <__iterator/iterator_traits.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 #if _LIBCPP_STD_VER >= 20 23 24 template <class _ForwardIterator> 25 inline _LIBCPP_HIDE_FROM_ABI constexpr _ForwardIterator 26 shift_left(_ForwardIterator __first, 27 _ForwardIterator __last, 28 typename iterator_traits<_ForwardIterator>::difference_type __n) { 29 if (__n == 0) { 30 return __last; 31 } 32 33 _ForwardIterator __m = __first; 34 if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value) { 35 if (__n >= __last - __first) { 36 return __first; 37 } 38 __m += __n; 39 } else { 40 for (; __n > 0; --__n) { 41 if (__m == __last) { 42 return __first; 43 } 44 ++__m; 45 } 46 } 47 return std::move(__m, __last, __first); 48 } 49 50 #endif // _LIBCPP_STD_VER >= 20 51 52 _LIBCPP_END_NAMESPACE_STD 53 54 #endif // _LIBCPP___ALGORITHM_SHIFT_LEFT_H 55