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// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_SVG_ANIMATION_PRIORITY_QUEUE_H_
#define THIRD_PARTY_BLINK_RENDERER_CORE_SVG_ANIMATION_PRIORITY_QUEUE_H_
#include "base/gtest_prod_util.h"
#include "base/macros.h"
#include "third_party/blink/renderer/platform/heap/heap_allocator.h"
#include "third_party/blink/renderer/platform/heap/member.h"
namespace blink {
// A basic priority queue based on a (binary min) heap.
//
// The queue tracks the position in the heap vector by storing (and
// maintaining) an index in the entry element itself using a
// PriorityQueueHandle() accessor.
//
// While it appears to be generic, it's currently only to make testing easier.
template <typename PriorityType, typename ElementType>
class PriorityQueue {
DISALLOW_NEW();
public:
using EntryType = std::pair<PriorityType, Member<ElementType>>;
using StorageType = HeapVector<EntryType>;
using iterator = typename StorageType::iterator;
using const_iterator = typename StorageType::const_iterator;
PriorityQueue() = default;
bool Contains(ElementType* element) const {
return element->PriorityQueueHandle() != kNotFound;
}
void Insert(PriorityType priority, ElementType* element);
// Updates the position of the specified object in the queue to the new
// priority |priority|.
void Update(PriorityType priority, ElementType* element);
void Remove(ElementType* element);
// Set the priority of all entries to |priority|.
void ResetAllPriorities(PriorityType priority);
wtf_size_t size() const { return heap_.size(); }
bool IsEmpty() const { return heap_.IsEmpty(); }
const PriorityType& Min() const { return heap_.front().first; }
ElementType* MinElement() const { return heap_.front().second; }
iterator begin() { return heap_.begin(); }
iterator end() { return heap_.end(); }
const_iterator begin() const { return heap_.begin(); }
const_iterator end() const { return heap_.end(); }
const EntryType& operator[](wtf_size_t index) const { return heap_[index]; }
void Trace(Visitor* visitor) const { visitor->Trace(heap_); }
private:
FRIEND_TEST_ALL_PREFIXES(PriorityQueueTest, Updates);
wtf_size_t PercolateUp(wtf_size_t index);
void PercolateDown(wtf_size_t index);
wtf_size_t SmallestChildIndex(wtf_size_t index) const;
static bool IsRoot(wtf_size_t index) { return index == 0; }
static wtf_size_t ParentIndex(wtf_size_t index) {
DCHECK_NE(index, 0u);
return (index - 1) / 2;
}
static wtf_size_t LeftChildIndex(wtf_size_t index) { return 2 * index + 1; }
static bool CompareLess(const EntryType& a, const EntryType& b) {
return a.first < b.first;
}
static void Swap(EntryType& a, EntryType& b) {
std::swap(a.second->PriorityQueueHandle(), b.second->PriorityQueueHandle());
std::swap(a, b);
}
StorageType heap_;
DISALLOW_COPY_AND_ASSIGN(PriorityQueue);
};
template <typename PriorityType, typename ElementType>
inline wtf_size_t PriorityQueue<PriorityType, ElementType>::PercolateUp(
wtf_size_t index) {
while (!IsRoot(index)) {
wtf_size_t parent_index = ParentIndex(index);
if (!CompareLess(heap_[index], heap_[parent_index]))
break;
Swap(heap_[index], heap_[parent_index]);
index = parent_index;
}
return index;
}
template <typename PriorityType, typename ElementType>
inline wtf_size_t PriorityQueue<PriorityType, ElementType>::SmallestChildIndex(
wtf_size_t index) const {
wtf_size_t left_child_index = LeftChildIndex(index);
if (left_child_index >= heap_.size())
return left_child_index;
wtf_size_t right_child_index = left_child_index + 1;
if (right_child_index < heap_.size() &&
CompareLess(heap_[right_child_index], heap_[left_child_index]))
return right_child_index;
return left_child_index;
}
template <typename PriorityType, typename ElementType>
inline void PriorityQueue<PriorityType, ElementType>::PercolateDown(
wtf_size_t index) {
while (true) {
wtf_size_t smallest_child_index = SmallestChildIndex(index);
if (smallest_child_index >= heap_.size())
break;
if (!CompareLess(heap_[smallest_child_index], heap_[index]))
break;
Swap(heap_[smallest_child_index], heap_[index]);
index = smallest_child_index;
}
}
template <typename PriorityType, typename ElementType>
inline void PriorityQueue<PriorityType, ElementType>::Insert(
PriorityType priority,
ElementType* element) {
DCHECK(!Contains(element));
heap_.push_back(EntryType{priority, element});
wtf_size_t new_index = heap_.size() - 1;
element->PriorityQueueHandle() = new_index;
PercolateUp(new_index);
}
template <typename PriorityType, typename ElementType>
inline void PriorityQueue<PriorityType, ElementType>::Remove(
ElementType* element) {
DCHECK(Contains(element));
wtf_size_t index = element->PriorityQueueHandle();
Swap(heap_[index], heap_.back());
heap_.pop_back();
element->PriorityQueueHandle() = kNotFound;
if (index == heap_.size() || PercolateUp(index) != index)
return;
PercolateDown(index);
}
template <typename PriorityType, typename ElementType>
inline void PriorityQueue<PriorityType, ElementType>::Update(
PriorityType priority,
ElementType* element) {
DCHECK(Contains(element));
wtf_size_t index = element->PriorityQueueHandle();
heap_[index].first = priority;
if (PercolateUp(index) != index)
return;
PercolateDown(index);
}
template <typename PriorityType, typename ElementType>
inline void PriorityQueue<PriorityType, ElementType>::ResetAllPriorities(
PriorityType priority) {
for (auto& entry : heap_)
entry.first = priority;
}
} // namespace blink
#endif // THIRD_PARTY_BLINK_RENDERER_CORE_SVG_ANIMATION_PRIORITY_QUEUE_H_
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