1 //
2 // Copyright (C) 2010 The Android Open Source Project
3 //
4 // Licensed under the Apache License, Version 2.0 (the "License");
5 // you may not use this file except in compliance with the License.
6 // You may obtain a copy of the License at
7 //
8 // http://www.apache.org/licenses/LICENSE-2.0
9 //
10 // Unless required by applicable law or agreed to in writing, software
11 // distributed under the License is distributed on an "AS IS" BASIS,
12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 // See the License for the specific language governing permissions and
14 // limitations under the License.
15 //
16 #include "update_engine/payload_generator/tarjan.h"
17
18 #include <algorithm>
19 #include <vector>
20
21 #include <base/logging.h>
22
23 #include "update_engine/common/utils.h"
24
25 using std::min;
26 using std::vector;
27
28 namespace chromeos_update_engine {
29
30 namespace {
31 const vector<Vertex>::size_type kInvalidIndex = -1;
32 }
33
Execute(Vertex::Index vertex,Graph * graph,vector<Vertex::Index> * out)34 void TarjanAlgorithm::Execute(Vertex::Index vertex,
35 Graph* graph,
36 vector<Vertex::Index>* out) {
37 stack_.clear();
38 components_.clear();
39 index_ = 0;
40 for (Graph::iterator it = graph->begin(); it != graph->end(); ++it)
41 it->index = it->lowlink = kInvalidIndex;
42 required_vertex_ = vertex;
43
44 Tarjan(vertex, graph);
45 if (!components_.empty())
46 out->swap(components_[0]);
47 }
48
Tarjan(Vertex::Index vertex,Graph * graph)49 void TarjanAlgorithm::Tarjan(Vertex::Index vertex, Graph* graph) {
50 CHECK_EQ((*graph)[vertex].index, kInvalidIndex);
51 (*graph)[vertex].index = index_;
52 (*graph)[vertex].lowlink = index_;
53 index_++;
54 stack_.push_back(vertex);
55 for (Vertex::EdgeMap::iterator it = (*graph)[vertex].out_edges.begin();
56 it != (*graph)[vertex].out_edges.end(); ++it) {
57 Vertex::Index vertex_next = it->first;
58 if ((*graph)[vertex_next].index == kInvalidIndex) {
59 Tarjan(vertex_next, graph);
60 (*graph)[vertex].lowlink = min((*graph)[vertex].lowlink,
61 (*graph)[vertex_next].lowlink);
62 } else if (utils::VectorContainsValue(stack_, vertex_next)) {
63 (*graph)[vertex].lowlink = min((*graph)[vertex].lowlink,
64 (*graph)[vertex_next].index);
65 }
66 }
67 if ((*graph)[vertex].lowlink == (*graph)[vertex].index) {
68 vector<Vertex::Index> component;
69 Vertex::Index other_vertex;
70 do {
71 other_vertex = stack_.back();
72 stack_.pop_back();
73 component.push_back(other_vertex);
74 } while (other_vertex != vertex && !stack_.empty());
75
76 if (utils::VectorContainsValue(component, required_vertex_)) {
77 components_.resize(components_.size() + 1);
78 component.swap(components_.back());
79 }
80 }
81 }
82
83 } // namespace chromeos_update_engine
84