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 #include <type_traits> 16 17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 18 # pragma GCC system_header 19 # pragma clang include_instead(<algorithm>) 20 #endif 21 22 _LIBCPP_BEGIN_NAMESPACE_STD 23 24 #if _LIBCPP_STD_VER > 17 25 26 template <class _ForwardIterator> 27 inline _LIBCPP_INLINE_VISIBILITY constexpr 28 _ForwardIterator 29 shift_left(_ForwardIterator __first, _ForwardIterator __last, 30 typename iterator_traits<_ForwardIterator>::difference_type __n) 31 { 32 if (__n == 0) { 33 return __last; 34 } 35 36 _ForwardIterator __m = __first; 37 if constexpr (__is_cpp17_random_access_iterator<_ForwardIterator>::value) { 38 if (__n >= __last - __first) { 39 return __first; 40 } 41 __m += __n; 42 } else { 43 for (; __n > 0; --__n) { 44 if (__m == __last) { 45 return __first; 46 } 47 ++__m; 48 } 49 } 50 return _VSTD::move(__m, __last, __first); 51 } 52 53 #endif // _LIBCPP_STD_VER > 17 54 55 _LIBCPP_END_NAMESPACE_STD 56 57 #endif // _LIBCPP___ALGORITHM_SHIFT_LEFT_H 58