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