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Diffstat (limited to 'libcxx/include/__iterator/advance.h')
| -rw-r--r-- | libcxx/include/__iterator/advance.h | 200 |
1 files changed, 200 insertions, 0 deletions
diff --git a/libcxx/include/__iterator/advance.h b/libcxx/include/__iterator/advance.h new file mode 100644 index 000000000000..47bce1ddfbe2 --- /dev/null +++ b/libcxx/include/__iterator/advance.h @@ -0,0 +1,200 @@ +// -*- 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 <__config> +#include <__debug> +#include <__function_like.h> +#include <__iterator/concepts.h> +#include <__iterator/incrementable_traits.h> +#include <__iterator/iterator_traits.h> +#include <__utility/move.h> +#include <cstdlib> +#include <concepts> +#include <limits> +#include <type_traits> + +#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_AFTER_CXX14 +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_AFTER_CXX14 +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_AFTER_CXX14 +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(declval<_Distance>())), + class = _EnableIf<is_integral<_IntegralDistance>::value> > +_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14 +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 !defined(_LIBCPP_HAS_NO_RANGES) + +namespace ranges { +// [range.iter.op.advance] +struct __advance_fn final : private __function_like { +private: + template <class _Tp> + _LIBCPP_HIDE_FROM_ABI + static constexpr _Tp __magnitude_geq(_Tp __a, _Tp __b) noexcept { + return __a < 0 ? (__a <= __b) : (__a >= __b); + } + + 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: + constexpr explicit __advance_fn(__tag __x) noexcept : __function_like(__x) {} + + // 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) denotes a range. + template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp> + _LIBCPP_HIDE_FROM_ABI + constexpr void operator()(_Ip& __i, _Sp __bound) const { + // If `I` and `S` model `assignable_from<I&, S>`, equivalent to `i = std::move(bound)`. + if constexpr (assignable_from<_Ip&, _Sp>) { + __i = _VSTD::move(__bound); + } + // Otherwise, if `S` and `I` model `sized_sentinel_for<S, I>`, equivalent to `ranges::advance(i, bound - i)`. + else if constexpr (sized_sentinel_for<_Sp, _Ip>) { + (*this)(__i, __bound - __i); + } + // Otherwise, while `bool(i != bound)` is true, increments `i`. + else { + while (__i != __bound) { + ++__i; + } + } + } + + // Preconditions: + // * If `n > 0`, [i, bound) denotes a range. + // * If `n == 0`, [i, bound) or [bound, i) denotes a range. + // * If `n < 0`, [bound, 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 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) 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 - i|, equivalent to `ranges::advance(i, bound)`. + if (const auto __M = __bound - __i; __magnitude_geq(__n, __M)) { + (*this)(__i, __bound); + 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)` is true, increments `i` but at + // most `n` times. + while (__i != __bound && __n > 0) { + ++__i; + --__n; + } + + // Otherwise, while `bool(i != bound)` is true, decrements `i` but at most `-n` times. + if constexpr (bidirectional_iterator<_Ip> && same_as<_Ip, _Sp>) { + while (__i != __bound && __n < 0) { + --__i; + ++__n; + } + } + return __n; + } + + _LIBCPP_UNREACHABLE(); + } +}; + +inline constexpr auto advance = __advance_fn(__function_like::__tag()); +} // namespace ranges + +#endif // !defined(_LIBCPP_HAS_NO_RANGES) + +_LIBCPP_END_NAMESPACE_STD + +_LIBCPP_POP_MACROS + +#endif // _LIBCPP___ITERATOR_ADVANCE_H |