// -*- 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>())),
__enable_if_t<is_integral<_IntegralDistance>::value, int> = 0>
_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 {
struct __advance {
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 (__n > 0 && __i != __bound_sentinel) {
++__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 (__n < 0 && __i != __bound_sentinel) {
--__i;
++__n;
}
}
return __n;
}
__libcpp_unreachable();
}
};
inline namespace __cpo {
inline constexpr auto advance = __advance{};
} // namespace __cpo
} // namespace ranges
#endif // _LIBCPP_STD_VER >= 20
_LIBCPP_END_NAMESPACE_STD
_LIBCPP_POP_MACROS
#endif // _LIBCPP___ITERATOR_ADVANCE_H
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