1 // Copyright 2020 The Pigweed Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
5 // the License at
6 //
7 //     https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
13 // the License.
14 
15 #include "pw_containers/intrusive_list.h"
16 
17 #include "pw_assert/assert.h"
18 
19 namespace pw::intrusive_list_impl {
20 
~Item()21 List::Item::~Item() { unlist(); }
22 
unlist(Item * prev)23 void List::Item::unlist(Item* prev) {
24   if (prev == nullptr) {
25     prev = previous();
26   }
27   // Skip over this.
28   prev->next_ = next_;
29 
30   // Retain the invariant that unlisted items are self-cycles.
31   next_ = this;
32 }
33 
previous()34 List::Item* List::Item::previous() {
35   // Follow the cycle around to find the previous element; O(N).
36   Item* prev = next_;
37   while (prev->next_ != this) {
38     prev = prev->next_;
39   }
40   return prev;
41 }
42 
insert_after(Item * pos,Item & item)43 void List::insert_after(Item* pos, Item& item) {
44   PW_CHECK(
45       item.unlisted(),
46       "Cannot add an item to a pw::IntrusiveList that is already in a list");
47   item.next_ = pos->next_;
48   pos->next_ = &item;
49 }
50 
erase_after(Item * pos)51 void List::erase_after(Item* pos) { pos->next_->unlist(pos); }
52 
before_end()53 List::Item* List::before_end() noexcept { return before_begin()->previous(); }
54 
clear()55 void List::clear() {
56   while (!empty()) {
57     erase_after(before_begin());
58   }
59 }
60 
remove(const Item & item_to_remove)61 bool List::remove(const Item& item_to_remove) {
62   for (Item* pos = before_begin(); pos->next_ != end(); pos = pos->next_) {
63     if (pos->next_ == &item_to_remove) {
64       erase_after(pos);
65       return true;
66     }
67   }
68   return false;
69 }
70 
size() const71 size_t List::size() const {
72   size_t total = 0;
73   Item* item = head_.next_;
74   while (item != &head_) {
75     item = item->next_;
76     total++;
77   }
78   return total;
79 }
80 
81 }  // namespace pw::intrusive_list_impl
82