// -*- C++ -*- //===----------------------------------------------------------------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// #ifndef _LIBCPP___ITERATOR_ADVANCE_H #define _LIBCPP___ITERATOR_ADVANCE_H #include <__assert> #include <__concepts/assignable.h> #include <__concepts/same_as.h> #include <__config> #include <__iterator/concepts.h> #include <__iterator/incrementable_traits.h> #include <__iterator/iterator_traits.h> #include <__type_traits/enable_if.h> #include <__type_traits/is_integral.h> #include <__utility/convert_to_integral.h> #include <__utility/declval.h> #include <__utility/move.h> #include <__utility/unreachable.h> #include <limits> #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) # pragma GCC system_header #endif _LIBCPP_PUSH_MACROS #include <__undef_macros> _LIBCPP_BEGIN_NAMESPACE_STD template <class _InputIter> _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 void __advance(_InputIter& __i, typename iterator_traits<_InputIter>::difference_type __n, input_iterator_tag) { for (; __n > 0; --__n) ++__i; } template <class _BiDirIter> _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 void __advance(_BiDirIter& __i, typename iterator_traits<_BiDirIter>::difference_type __n, bidirectional_iterator_tag) { if (__n >= 0) for (; __n > 0; --__n) ++__i; else for (; __n < 0; ++__n) --__i; } template <class _RandIter> _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 void __advance(_RandIter& __i, typename iterator_traits<_RandIter>::difference_type __n, random_access_iterator_tag) { __i += __n; } template < class _InputIter, class _Distance, class _IntegralDistance = decltype(std::__convert_to_integral(std::declval<_Distance>())), class = __enable_if_t<is_integral<_IntegralDistance>::value> > _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 void advance(_InputIter& __i, _Distance __orig_n) { typedef typename iterator_traits<_InputIter>::difference_type _Difference; _Difference __n = static_cast<_Difference>(std::__convert_to_integral(__orig_n)); // Calling `advance` with a negative value on a non-bidirectional iterator is a no-op in the current implementation. _LIBCPP_ASSERT_PEDANTIC(__n >= 0 || __has_bidirectional_iterator_category<_InputIter>::value, "Attempt to advance(it, n) with negative n on a non-bidirectional iterator"); std::__advance(__i, __n, typename iterator_traits<_InputIter>::iterator_category()); } #if _LIBCPP_STD_VER >= 20 // [range.iter.op.advance] namespace ranges { namespace __advance { struct __fn { private: template <class _Ip> _LIBCPP_HIDE_FROM_ABI static constexpr void __advance_forward(_Ip& __i, iter_difference_t<_Ip> __n) { while (__n > 0) { --__n; ++__i; } } template <class _Ip> _LIBCPP_HIDE_FROM_ABI static constexpr void __advance_backward(_Ip& __i, iter_difference_t<_Ip> __n) { while (__n < 0) { ++__n; --__i; } } public: // Preconditions: If `I` does not model `bidirectional_iterator`, `n` is not negative. template <input_or_output_iterator _Ip> _LIBCPP_HIDE_FROM_ABI constexpr void operator()(_Ip& __i, iter_difference_t<_Ip> __n) const { // Calling `advance` with a negative value on a non-bidirectional iterator is a no-op in the current implementation. _LIBCPP_ASSERT_PEDANTIC( __n >= 0 || bidirectional_iterator<_Ip>, "If `n < 0`, then `bidirectional_iterator<I>` must be true."); // If `I` models `random_access_iterator`, equivalent to `i += n`. if constexpr (random_access_iterator<_Ip>) { __i += __n; return; } else if constexpr (bidirectional_iterator<_Ip>) { // Otherwise, if `n` is non-negative, increments `i` by `n`. __advance_forward(__i, __n); // Otherwise, decrements `i` by `-n`. __advance_backward(__i, __n); return; } else { // Otherwise, if `n` is non-negative, increments `i` by `n`. __advance_forward(__i, __n); return; } } // Preconditions: Either `assignable_from<I&, S> || sized_sentinel_for<S, I>` is modeled, or [i, bound_sentinel) // denotes a range. template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> _LIBCPP_HIDE_FROM_ABI constexpr void operator()(_Ip& __i, _Sp __bound_sentinel) const { // If `I` and `S` model `assignable_from<I&, S>`, equivalent to `i = std::move(bound_sentinel)`. if constexpr (assignable_from<_Ip&, _Sp>) { __i = std::move(__bound_sentinel); } // Otherwise, if `S` and `I` model `sized_sentinel_for<S, I>`, equivalent to `ranges::advance(i, bound_sentinel - // i)`. else if constexpr (sized_sentinel_for<_Sp, _Ip>) { (*this)(__i, __bound_sentinel - __i); } // Otherwise, while `bool(i != bound_sentinel)` is true, increments `i`. else { while (__i != __bound_sentinel) { ++__i; } } } // Preconditions: // * If `n > 0`, [i, bound_sentinel) denotes a range. // * If `n == 0`, [i, bound_sentinel) or [bound_sentinel, i) denotes a range. // * If `n < 0`, [bound_sentinel, i) denotes a range, `I` models `bidirectional_iterator`, and `I` and `S` model // `same_as<I, S>`. // Returns: `n - M`, where `M` is the difference between the ending and starting position. template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> _LIBCPP_HIDE_FROM_ABI constexpr iter_difference_t<_Ip> operator()(_Ip& __i, iter_difference_t<_Ip> __n, _Sp __bound_sentinel) const { // Calling `advance` with a negative value on a non-bidirectional iterator is a no-op in the current implementation. _LIBCPP_ASSERT_PEDANTIC((__n >= 0) || (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>), "If `n < 0`, then `bidirectional_iterator<I> && same_as<I, S>` must be true."); // If `S` and `I` model `sized_sentinel_for<S, I>`: if constexpr (sized_sentinel_for<_Sp, _Ip>) { // If |n| >= |bound_sentinel - i|, equivalent to `ranges::advance(i, bound_sentinel)`. // __magnitude_geq(a, b) returns |a| >= |b|, assuming they have the same sign. auto __magnitude_geq = [](auto __a, auto __b) { return __a == 0 ? __b == 0 : __a > 0 ? __a >= __b : __a <= __b; }; if (const auto __m = __bound_sentinel - __i; __magnitude_geq(__n, __m)) { (*this)(__i, __bound_sentinel); return __n - __m; } // Otherwise, equivalent to `ranges::advance(i, n)`. (*this)(__i, __n); return 0; } else { // Otherwise, if `n` is non-negative, while `bool(i != bound_sentinel)` is true, increments `i` but at // most `n` times. while (__i != __bound_sentinel && __n > 0) { ++__i; --__n; } // Otherwise, while `bool(i != bound_sentinel)` is true, decrements `i` but at most `-n` times. if constexpr (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>) { while (__i != __bound_sentinel && __n < 0) { --__i; ++__n; } } return __n; } __libcpp_unreachable(); } }; } // namespace __advance inline namespace __cpo { inline constexpr auto advance = __advance::__fn{}; } // namespace __cpo } // namespace ranges #endif // _LIBCPP_STD_VER >= 20 _LIBCPP_END_NAMESPACE_STD _LIBCPP_POP_MACROS #endif // _LIBCPP___ITERATOR_ADVANCE_H