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// Copyright 2020 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#include "pw_containers/intrusive_list.h"
#include <utility>
#include "pw_assert/check.h"
namespace pw::intrusive_list_impl {
List::Item::Item(Item&& other) {
// Ensure `next_` is valid on instantiation.
next_ = this;
*this = std::move(other);
}
List::Item& List::Item::operator=(List::Item&& other) {
// Remove `this` object from its current list.
if (!unlisted()) {
unlist();
}
// If `other` is listed, remove it from its list and put `this` in its place.
if (!other.unlisted()) {
List::Item* prev = other.previous();
other.unlist(prev);
List::insert_after(prev, *this);
}
return *this;
}
void List::Item::unlist(Item* prev) {
if (prev == nullptr) {
prev = previous();
}
// Skip over this.
prev->next_ = next_;
// Retain the invariant that unlisted items are self-cycles.
next_ = this;
}
List::Item* List::Item::previous() {
// Follow the cycle around to find the previous element; O(N).
Item* prev = next_;
while (prev->next_ != this) {
prev = prev->next_;
}
return prev;
}
void List::insert_after(Item* pos, Item& item) {
PW_CHECK(
item.unlisted(),
"Cannot add an item to a pw::IntrusiveList that is already in a list");
item.next_ = pos->next_;
pos->next_ = &item;
}
void List::erase_after(Item* pos) { pos->next_->unlist(pos); }
List::Item* List::before_end() noexcept { return before_begin()->previous(); }
void List::clear() {
while (!empty()) {
erase_after(before_begin());
}
}
bool List::remove(const Item& item_to_remove) {
for (Item* pos = before_begin(); pos->next_ != end(); pos = pos->next_) {
if (pos->next_ == &item_to_remove) {
erase_after(pos);
return true;
}
}
return false;
}
size_t List::size() const {
size_t total = 0;
Item* item = head_.next_;
while (item != &head_) {
item = item->next_;
total++;
}
return total;
}
} // namespace pw::intrusive_list_impl
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