| // -*- 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_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(_VSTD::__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>(_VSTD::__convert_to_integral(__orig_n)); |
| _LIBCPP_ASSERT(__n >= 0 || __is_cpp17_bidirectional_iterator<_InputIter>::value, |
| "Attempt to advance(it, n) with negative n on a non-bidirectional iterator"); |
| _VSTD::__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 { |
| _LIBCPP_ASSERT(__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 = _VSTD::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 { |
| _LIBCPP_ASSERT((__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 |
| |
| #endif // _LIBCPP___ITERATOR_ADVANCE_H |