001 /*
002 * Sonar, open source software quality management tool.
003 * Copyright (C) 2008-2011 SonarSource
004 * mailto:contact AT sonarsource DOT com
005 *
006 * Sonar is free software; you can redistribute it and/or
007 * modify it under the terms of the GNU Lesser General Public
008 * License as published by the Free Software Foundation; either
009 * version 3 of the License, or (at your option) any later version.
010 *
011 * Sonar is distributed in the hope that it will be useful,
012 * but WITHOUT ANY WARRANTY; without even the implied warranty of
013 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014 * Lesser General Public License for more details.
015 *
016 * You should have received a copy of the GNU Lesser General Public
017 * License along with Sonar; if not, write to the Free Software
018 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02
019 */
020 package org.sonar.duplications.detector.original;
021
022 import java.util.Collection;
023 import java.util.Collections;
024 import java.util.List;
025 import java.util.Map;
026
027 import org.sonar.duplications.block.Block;
028 import org.sonar.duplications.block.ByteArray;
029 import org.sonar.duplications.index.CloneGroup;
030 import org.sonar.duplications.index.CloneIndex;
031 import org.sonar.duplications.index.ClonePart;
032
033 import com.google.common.collect.Lists;
034 import com.google.common.collect.Maps;
035
036 /**
037 * Implementation of algorithm described in paper
038 * <a href="http://www4.in.tum.de/~juergens/publications/icsm2010_crc.pdf">Index-Based Code Clone Detection: Incremental, Distributed, Scalable</a>
039 * by Benjamin Hummel, Elmar Juergens, Michael Conradt and Lars Heinemann.
040 */
041 public final class OriginalCloneDetectionAlgorithm {
042
043 /**
044 * Performs detection and returns list of clone groups between file (which represented as a collection of blocks) and index.
045 * Note that this method ignores blocks for this file, that will be retrieved from index.
046 */
047 public static List<CloneGroup> detect(CloneIndex cloneIndex, Collection<Block> fileBlocks) {
048 if (fileBlocks.isEmpty()) {
049 return Collections.EMPTY_LIST;
050 }
051 OriginalCloneDetectionAlgorithm reporter = new OriginalCloneDetectionAlgorithm(cloneIndex);
052 reporter.findClones(fileBlocks);
053 return reporter.filter.getResult();
054 }
055
056 private final CloneIndex cloneIndex;
057
058 private final Filter filter = new Filter();
059
060 private String originResourceId;
061
062 private OriginalCloneDetectionAlgorithm(CloneIndex cloneIndex) {
063 this.cloneIndex = cloneIndex;
064 }
065
066 private BlocksGroup[] createGroups(Collection<Block> fileBlocks) {
067 // 2: let f be the list of tuples corresponding to filename sorted by statement index
068 // either read from the index or calculated on the fly
069 int size = fileBlocks.size();
070
071 // Godin: create one group per unique hash
072 Map<ByteArray, BlocksGroup> groupsByHash = Maps.newHashMap(); // TODO Godin: can we create map with expected size?
073 for (Block fileBlock : fileBlocks) {
074 ByteArray hash = fileBlock.getBlockHash();
075 BlocksGroup sameHash = groupsByHash.get(hash);
076 if (sameHash == null) {
077 sameHash = BlocksGroup.empty();
078 groupsByHash.put(hash, sameHash);
079 }
080 sameHash.blocks.add(fileBlock);
081 }
082
083 // Godin: retrieve blocks from index
084 for (Map.Entry<ByteArray, BlocksGroup> entry : groupsByHash.entrySet()) {
085 ByteArray hash = entry.getKey();
086 BlocksGroup group = entry.getValue();
087 for (Block blockFromIndex : cloneIndex.getBySequenceHash(hash)) {
088 // Godin: skip blocks for this file if they come from index
089 if (!originResourceId.equals(blockFromIndex.getResourceId())) {
090 group.blocks.add(blockFromIndex);
091 }
092 }
093 Collections.sort(group.blocks, BlocksGroup.BlockComparator.INSTANCE);
094 }
095
096 // 3: let c be a list with c(0) = empty
097 BlocksGroup[] sameHashBlocksGroups = new BlocksGroup[size + 2];
098 sameHashBlocksGroups[0] = BlocksGroup.empty();
099 // 4: for i := 1 to length(f) do
100 for (Block fileBlock : fileBlocks) {
101 ByteArray hash = fileBlock.getBlockHash();
102 int i = fileBlock.getIndexInFile() + 1;
103 // 5: retrieve tuples with same sequence hash as f(i)
104 // 6: store this set as c(i)
105 sameHashBlocksGroups[i] = groupsByHash.get(hash);
106 }
107
108 // Godin: allows to report clones at the end of file, because condition at line 13 would be evaluated as true
109 sameHashBlocksGroups[size + 1] = BlocksGroup.empty();
110
111 return sameHashBlocksGroups;
112 }
113
114 private void findClones(Collection<Block> fileBlocks) {
115 originResourceId = fileBlocks.iterator().next().getResourceId();
116
117 BlocksGroup[] sameHashBlocksGroups = createGroups(fileBlocks);
118
119 // 7: for i := 1 to length(c) do
120 for (int i = 1; i < sameHashBlocksGroups.length; i++) {
121 // In the main loop (starting from Line 7), we first check
122 // whether any new clones might start at this position. If there
123 // is only a single tuple with this hash (which has to belong
124 // to the inspected file at the current location) we skip this loop
125 // iteration. The same holds if all tuples at position i have already
126 // been present at position i − 1, as in this case any clone group
127 // found at position i would be included in a clone group starting
128 // at position i − 1.
129
130 // Although we use the subset operator in the
131 // algorithm description, this is not really a subset operation,
132 // as of course the statement index of the tuples in c(i) will be
133 // increased by 1 compared to the corresponding ones in c(i − 1)
134 // and the hash and info fields will differ.
135
136 // 8: if |c(i)| < 2 or c(i) subsumed by c(i - 1) then
137 if (sameHashBlocksGroups[i].size() < 2 || sameHashBlocksGroups[i].subsumedBy(sameHashBlocksGroups[i - 1], 1)) {
138 // 9: continue with next loop iteration
139 continue;
140 }
141
142 // The set a introduced in Line 10 is called the active set and
143 // contains all tuples corresponding to clones which have not yet
144 // been reported. At each iteration of the inner loop the set a
145 // is reduced to tuples which are also present in c(j); again the
146 // intersection operator has to account for the increased statement
147 // index and different hash and info fields. The new value is
148 // stored in a0. Clones are only reported, if tuples are lost in
149 // Line 12, as otherwise all current clones could be prolonged
150 // by one statement. Clone reporting matches tuples that, after
151 // correction of the statement index, appear in both c(i) and a;
152 // each matched pair corresponds to a single clone. Its location
153 // can be extracted from the filename and info fields.
154
155 // 10: let a := c(i)
156 BlocksGroup currentBlocksGroup = sameHashBlocksGroups[i];
157 // 11: for j := i + 1 to length(c) do
158 for (int j = i + 1; j < sameHashBlocksGroups.length; j++) {
159 // 12: let a0 := a intersect c(j)
160 BlocksGroup intersectedBlocksGroup = currentBlocksGroup.intersect(sameHashBlocksGroups[j]);
161
162 // 13: if |a0| < |a| then
163 if (intersectedBlocksGroup.size() < currentBlocksGroup.size()) {
164 // 14: report clones from c(i) to a (see text)
165
166 // One problem of this algorithm is that clone classes with
167 // multiple instances in the same file are encountered and
168 // reported multiple times. Furthermore, when calculating the clone
169 // groups for all files in a system, clone groups will be reported
170 // more than once as well. Both cases can be avoided, by
171 // checking whether the first element of a0 (with respect to a
172 // fixed order) is equal to f(j) and only report in this case.
173
174 Block first = currentBlocksGroup.first(originResourceId);
175 if (first.getIndexInFile() == j - 2) {
176 // Godin: We report clones, which start in i-1 and end in j-2, so length is j-2-(i-1)+1=j-i
177 reportClones(sameHashBlocksGroups[i], currentBlocksGroup, j - i);
178 }
179 }
180 // 15: a := a0
181 currentBlocksGroup = intersectedBlocksGroup;
182
183 // Line 16 early exits the inner loop if either no more clones are starting
184 // from position i (i.e., a is too small), or if all tuples from a
185 // have already been in c(i − 1), corrected for statement index.
186 // In this case they have already been reported in the previous
187 // iteration of the outer loop.
188
189 // IMPORTANT Godin: note that difference in indexes between "a" and "c(i-1)" greater than one,
190 // so method subsumedBy should take this into account
191
192 // 16: if |a| < 2 or a subsumed by c(i-1) then
193 if (currentBlocksGroup.size() < 2 || currentBlocksGroup.subsumedBy(sameHashBlocksGroups[i - 1], j - i + 1)) {
194 // 17: break inner loop
195 break;
196 }
197 }
198 }
199 }
200
201 private void reportClones(BlocksGroup beginGroup, BlocksGroup endGroup, int cloneLength) {
202 List<Block[]> pairs = beginGroup.pairs(endGroup, cloneLength);
203
204 ClonePart origin = null;
205 List<ClonePart> parts = Lists.newArrayList();
206
207 for (int i = 0; i < pairs.size(); i++) {
208 Block[] pair = pairs.get(i);
209 Block firstBlock = pair[0];
210 Block lastBlock = pair[1];
211 ClonePart part = new ClonePart(firstBlock.getResourceId(),
212 firstBlock.getIndexInFile(),
213 firstBlock.getFirstLineNumber(),
214 lastBlock.getLastLineNumber());
215
216 if (originResourceId.equals(part.getResourceId())) {
217 if (origin == null) {
218 origin = part;
219 } else if (part.getUnitStart() < origin.getUnitStart()) {
220 origin = part;
221 }
222 }
223
224 parts.add(part);
225 }
226
227 filter.add(new CloneGroup(cloneLength, origin, parts));
228 }
229
230 }