747eb149d0
Bug: 116614593 Test: build with WITH_TIDY=1 Change-Id: I5a7461386946ca623ab509609092aa0ac8418b80
138 lines
3.5 KiB
C++
138 lines
3.5 KiB
C++
/*
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* Copyright (C) 2016 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// Based on system/update_engine/payload_generator/tarjan.cc
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#ifndef LIBMEMUNREACHABLE_TARJAN_H_
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#define LIBMEMUNREACHABLE_TARJAN_H_
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#include <assert.h>
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#include <algorithm>
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#include "Allocator.h"
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namespace android {
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template <class T>
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class Node {
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public:
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allocator::set<Node<T>*> references_in;
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allocator::set<Node<T>*> references_out;
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size_t index;
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size_t lowlink;
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T* ptr;
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Node(T* ptr, Allocator<Node> allocator)
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: references_in(allocator), references_out(allocator), ptr(ptr){};
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Node(Node&& rhs) noexcept = default;
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void Edge(Node<T>* ref) {
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references_out.emplace(ref);
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ref->references_in.emplace(this);
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}
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template <class F>
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void Foreach(F&& f) {
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for (auto& node : references_out) {
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f(node->ptr);
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}
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}
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private:
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DISALLOW_COPY_AND_ASSIGN(Node<T>);
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};
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template <class T>
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using Graph = allocator::vector<Node<T>*>;
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template <class T>
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using SCC = allocator::vector<Node<T>*>;
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template <class T>
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using SCCList = allocator::vector<SCC<T>>;
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template <class T>
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class TarjanAlgorithm {
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public:
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explicit TarjanAlgorithm(Allocator<void> allocator)
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: index_(0), stack_(allocator), components_(allocator) {}
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void Execute(Graph<T>& graph, SCCList<T>& out);
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private:
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static constexpr size_t UNDEFINED_INDEX = static_cast<size_t>(-1);
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void Tarjan(Node<T>* vertex, Graph<T>& graph);
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size_t index_;
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allocator::vector<Node<T>*> stack_;
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SCCList<T> components_;
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};
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template <class T>
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void TarjanAlgorithm<T>::Execute(Graph<T>& graph, SCCList<T>& out) {
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stack_.clear();
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components_.clear();
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index_ = 0;
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for (auto& it : graph) {
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it->index = UNDEFINED_INDEX;
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it->lowlink = UNDEFINED_INDEX;
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}
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for (auto& it : graph) {
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if (it->index == UNDEFINED_INDEX) {
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Tarjan(it, graph);
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}
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}
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out.swap(components_);
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}
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template <class T>
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void TarjanAlgorithm<T>::Tarjan(Node<T>* vertex, Graph<T>& graph) {
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assert(vertex->index == UNDEFINED_INDEX);
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vertex->index = index_;
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vertex->lowlink = index_;
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index_++;
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stack_.push_back(vertex);
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for (auto& it : vertex->references_out) {
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Node<T>* vertex_next = it;
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if (vertex_next->index == UNDEFINED_INDEX) {
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Tarjan(vertex_next, graph);
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vertex->lowlink = std::min(vertex->lowlink, vertex_next->lowlink);
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} else if (std::find(stack_.begin(), stack_.end(), vertex_next) != stack_.end()) {
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vertex->lowlink = std::min(vertex->lowlink, vertex_next->index);
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}
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}
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if (vertex->lowlink == vertex->index) {
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SCC<T> component{components_.get_allocator()};
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Node<T>* other_vertex;
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do {
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other_vertex = stack_.back();
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stack_.pop_back();
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component.push_back(other_vertex);
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} while (other_vertex != vertex && !stack_.empty());
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components_.emplace_back(component);
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}
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}
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template <class T>
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void Tarjan(Graph<T>& graph, SCCList<T>& out) {
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TarjanAlgorithm<T> tarjan{graph.get_allocator()};
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tarjan.Execute(graph, out);
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}
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} // namespace android
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#endif // LIBMEMUNREACHABLE_TARJAN_H_
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