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_INLINE_VISIBILITY constexpr 26 _ForwardIterator 27 shift_left(_ForwardIterator __first, _ForwardIterator __last, 28 typename iterator_traits<_ForwardIterator>::difference_type __n) 29 { 30 if (__n == 0) { 31 return __last; 32 } 33 34 _ForwardIterator __m = __first; 35 if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value) { 36 if (__n >= __last - __first) { 37 return __first; 38 } 39 __m += __n; 40 } else { 41 for (; __n > 0; --__n) { 42 if (__m == __last) { 43 return __first; 44 } 45 ++__m; 46 } 47 } 48 return _VSTD::move(__m, __last, __first); 49 } 50 51 #endif // _LIBCPP_STD_VER >= 20 52 53 _LIBCPP_END_NAMESPACE_STD 54 55 #endif // _LIBCPP___ALGORITHM_SHIFT_LEFT_H 56