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// -*- 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_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 = __enable_if_t<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]
// TODO(varconst): rename `__advance_fn` to `__fn`.
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
#endif // _LIBCPP___ITERATOR_ADVANCE_H
|
