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/*
* Copyright (C) 2016 The Android Open Source Project
*
* 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
*
* http://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.
*/
// Based on system/update_engine/payload_generator/tarjan.cc
#ifndef LIBMEMUNREACHABLE_TARJAN_H_
#define LIBMEMUNREACHABLE_TARJAN_H_
#include <assert.h>
#include <algorithm>
#include "Allocator.h"
template<class T>
class Node {
public:
allocator::set<Node<T>*> references_in;
allocator::set<Node<T>*> references_out;
size_t index;
size_t lowlink;
T* ptr;
Node(T* ptr, Allocator<Node> allocator) : references_in(allocator), references_out(allocator),
ptr(ptr) {};
Node(Node&& rhs) = default;
void Edge(Node<T>* ref) {
references_out.emplace(ref);
ref->references_in.emplace(this);
}
template<class F>
void Foreach(F&& f) {
for (auto& node: references_out) {
f(node->ptr);
}
}
private:
DISALLOW_COPY_AND_ASSIGN(Node<T>);
};
template<class T>
using Graph = allocator::vector<Node<T>*>;
template<class T>
using SCC = allocator::vector<Node<T>*>;
template<class T>
using SCCList = allocator::vector<SCC<T>>;
template<class T>
class TarjanAlgorithm {
public:
explicit TarjanAlgorithm(Allocator<void> allocator) : index_(0),
stack_(allocator), components_(allocator) {}
void Execute(Graph<T>& graph, SCCList<T>& out);
private:
static constexpr size_t UNDEFINED_INDEX = static_cast<size_t>(-1);
void Tarjan(Node<T>* vertex, Graph<T>& graph);
size_t index_;
allocator::vector<Node<T>*> stack_;
SCCList<T> components_;
};
template<class T>
void TarjanAlgorithm<T>::Execute(Graph<T>& graph, SCCList<T>& out) {
stack_.clear();
components_.clear();
index_ = 0;
for (auto& it: graph) {
it->index = UNDEFINED_INDEX;
it->lowlink = UNDEFINED_INDEX;
}
for (auto& it: graph) {
if (it->index == UNDEFINED_INDEX) {
Tarjan(it, graph);
}
}
out.swap(components_);
}
template<class T>
void TarjanAlgorithm<T>::Tarjan(Node<T>* vertex, Graph<T>& graph) {
assert(vertex->index == UNDEFINED_INDEX);
vertex->index = index_;
vertex->lowlink = index_;
index_++;
stack_.push_back(vertex);
for (auto& it: vertex->references_out) {
Node<T>* vertex_next = it;
if (vertex_next->index == UNDEFINED_INDEX) {
Tarjan(vertex_next, graph);
vertex->lowlink = std::min(vertex->lowlink, vertex_next->lowlink);
} else if (std::find(stack_.begin(), stack_.end(), vertex_next) != stack_.end()) {
vertex->lowlink = std::min(vertex->lowlink, vertex_next->index);
}
}
if (vertex->lowlink == vertex->index) {
SCC<T> component{components_.get_allocator()};
Node<T>* other_vertex;
do {
other_vertex = stack_.back();
stack_.pop_back();
component.push_back(other_vertex);
} while (other_vertex != vertex && !stack_.empty());
components_.emplace_back(component);
}
}
template<class T>
void Tarjan(Graph<T>& graph, SCCList<T>& out) {
TarjanAlgorithm<T> tarjan{graph.get_allocator()};
tarjan.Execute(graph, out);
}
#endif // LIBMEMUNREACHABLE_TARJAN_H_
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