blame: Compute the origin of lines in a result file

BlameGenerator digs through history and discovers the origin of each
line of some result file.  BlameResult consumes the stream of regions
created by the generator and lays them out in a table for applications
to display alongside of source lines.

Applications may optionally push in the working tree copy of a file
using the push(String, byte[]) method, allowing the application to
receive accurate line annotations for the working tree version.  Lines
that are uncommitted (difference between HEAD and working tree) will
show up with the description given by the application as the author,
or "Not Committed Yet" as a default string.

Applications may also run the BlameGenerator in reverse mode using the
reverse(AnyObjectId, AnyObjectId) method instead of push().  When
running in the reverse mode the generator annotates lines by the
commit they are removed in, rather than the commit they were added in.
This allows a user to discover where a line disappeared from when they
are looking at an older revision in the repository.  For example:

  blame --reverse 16e810b2..master -L 1080, org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/RefDirectoryTest.java
           (                                              1080)   }
  2302a6d3 (Christian Halstrick 2011-05-20 11:18:20 +0200 1081)
  2302a6d3 (Christian Halstrick 2011-05-20 11:18:20 +0200 1082)   /**
  2302a6d3 (Christian Halstrick 2011-05-20 11:18:20 +0200 1083)    * Kick the timestamp of a local file.

Above we learn that line 1080 (a closing curly brace of the prior
method) still exists in branch master, but the Javadoc comment below
it has been removed by Christian Halstrick on May 20th as part of
commit 2302a6d3.  This result differs considerably from that of C
Git's blame --reverse feature.  JGit tells the reader which commit
performed the delete, while C Git tells the reader the last commit
that still contained the line, leaving it an exercise to the reader
to discover the descendant that performed the removal.

This is still only a basic implementation.  Quite notably it is
missing support for the smart block copy/move detection that the C
implementation of `git blame` is well known for.  Despite being
incremental, the BlameGenerator can only be run once.  After the
generator runs it cannot be reused.  A better implementation would
support applications browsing through history efficiently.

In regards to CQ 5110, only a little of the original code survives.

CQ: 5110
Bug: 306161
Change-Id: I84b8ea4838bb7d25f4fcdd540547884704661b8f
Signed-off-by: Kevin Sawicki <kevin@github.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

10 files changed, 2191 insertions, 0 deletions

diff --git a/org.eclipse.jgit/META-INF/MANIFEST.MF b/org.eclipse.jgit/META-INF/MANIFEST.MF
index e2d1a1e0ab..0788b8c621 100644
--- a/org.eclipse.jgit/META-INF/MANIFEST.MF
+++ b/org.eclipse.jgit/META-INF/MANIFEST.MF
@@ -8,6 +8,7 @@ Bundle-Vendor: %provider_name
 Export-Package: org.eclipse.jgit;version="1.0.0",
  org.eclipse.jgit.api;version="1.0.0",
  org.eclipse.jgit.api.errors;version="1.0.0",
+ org.eclipse.jgit.blame;version="1.0.0",
  org.eclipse.jgit.diff;version="1.0.0",
  org.eclipse.jgit.dircache;version="1.0.0",
  org.eclipse.jgit.errors;version="1.0.0",
diff --git a/org.eclipse.jgit/resources/org/eclipse/jgit/JGitText.properties b/org.eclipse.jgit/resources/org/eclipse/jgit/JGitText.properties
index 8eab4122c6..5a40edd7dc 100644
--- a/org.eclipse.jgit/resources/org/eclipse/jgit/JGitText.properties
+++ b/org.eclipse.jgit/resources/org/eclipse/jgit/JGitText.properties
@@ -32,6 +32,7 @@ badSectionEntry=Bad section entry: {0}
 base64InputNotProperlyPadded=Base64 input not properly padded.
 baseLengthIncorrect=base length incorrect
 bareRepositoryNoWorkdirAndIndex=Bare Repository has neither a working tree, nor an index
+blameNotCommittedYet=Not Committed Yet
 blobNotFound=Blob not found: {0}
 branchNameInvalid=Branch name {0} is not allowed
 blobNotFoundForPath=Blob not found: {0} for path: {1}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/JGitText.java b/org.eclipse.jgit/src/org/eclipse/jgit/JGitText.java
index 366028a2a7..02538a2dce 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/JGitText.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/JGitText.java
@@ -92,6 +92,7 @@ public class JGitText extends TranslationBundle {
 	/***/ public String base64InputNotProperlyPadded;
 	/***/ public String baseLengthIncorrect;
 	/***/ public String bareRepositoryNoWorkdirAndIndex;
+	/***/ public String blameNotCommittedYet;
 	/***/ public String blobNotFound;
 	/***/ public String blobNotFoundForPath;
 	/***/ public String branchNameInvalid;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/BlameCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/BlameCommand.java
new file mode 100644
index 0000000000..400d94bc88
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/BlameCommand.java
@@ -0,0 +1,227 @@
+/*
+ * Copyright (C) 2011, GitHub Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.api;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+
+import org.eclipse.jgit.api.errors.JGitInternalException;
+import org.eclipse.jgit.blame.BlameGenerator;
+import org.eclipse.jgit.blame.BlameResult;
+import org.eclipse.jgit.diff.DiffAlgorithm;
+import org.eclipse.jgit.diff.RawText;
+import org.eclipse.jgit.diff.RawTextComparator;
+import org.eclipse.jgit.dircache.DirCache;
+import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.Repository;
+
+/**
+ * Blame command for building a {@link BlameResult} for a file path.
+ */
+public class BlameCommand extends GitCommand<BlameResult> {
+
+	private String path;
+
+	private DiffAlgorithm diffAlgorithm;
+
+	private RawTextComparator textComparator;
+
+	private ObjectId startCommit;
+
+	private Collection<ObjectId> reverseEndCommits;
+
+	private Boolean followFileRenames;
+
+	/**
+	 * @param repo
+	 */
+	public BlameCommand(Repository repo) {
+		super(repo);
+	}
+
+	/**
+	 * Set file path
+	 *
+	 * @param filePath
+	 * @return this command
+	 */
+	public BlameCommand setFilePath(String filePath) {
+		this.path = filePath;
+		return this;
+	}
+
+	/**
+	 * Set diff algorithm
+	 *
+	 * @param diffAlgorithm
+	 * @return this command
+	 */
+	public BlameCommand setDiffAlgorithm(DiffAlgorithm diffAlgorithm) {
+		this.diffAlgorithm = diffAlgorithm;
+		return this;
+	}
+
+	/**
+	 * Set raw text comparator
+	 *
+	 * @param textComparator
+	 * @return this command
+	 */
+	public BlameCommand setTextComparator(RawTextComparator textComparator) {
+		this.textComparator = textComparator;
+		return this;
+	}
+
+	/**
+	 * Set start commit id
+	 *
+	 * @param commit
+	 * @return this command
+	 */
+	public BlameCommand setStartCommit(AnyObjectId commit) {
+		this.startCommit = commit.toObjectId();
+		return this;
+	}
+
+	/**
+	 * Enable (or disable) following file renames.
+	 * <p>
+	 * If true renames are followed using the standard FollowFilter behavior
+	 * used by RevWalk (which matches {@code git log --follow} in the C
+	 * implementation). This is not the same as copy/move detection as
+	 * implemented by the C implementation's of {@code git blame -M -C}.
+	 *
+	 * @param follow
+	 *            enable following.
+	 * @return {@code this}
+	 */
+	public BlameCommand setFollowFileRenames(boolean follow) {
+		followFileRenames = Boolean.valueOf(follow);
+		return this;
+	}
+
+	/**
+	 * Configure the command to compute reverse blame (history of deletes).
+	 *
+	 * @param start
+	 *            oldest commit to traverse from. The result file will be loaded
+	 *            from this commit's tree.
+	 * @param end
+	 *            most recent commit to stop traversal at. Usually an active
+	 *            branch tip, tag, or HEAD.
+	 * @return {@code this}
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public BlameCommand reverse(AnyObjectId start, AnyObjectId end)
+			throws IOException {
+		return reverse(start, Collections.singleton(end.toObjectId()));
+	}
+
+	/**
+	 * Configure the generator to compute reverse blame (history of deletes).
+	 *
+	 * @param start
+	 *            oldest commit to traverse from. The result file will be loaded
+	 *            from this commit's tree.
+	 * @param end
+	 *            most recent commits to stop traversal at. Usually an active
+	 *            branch tip, tag, or HEAD.
+	 * @return {@code this}
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public BlameCommand reverse(AnyObjectId start, Collection<ObjectId> end)
+			throws IOException {
+		startCommit = start.toObjectId();
+		reverseEndCommits = new ArrayList<ObjectId>(end);
+		return this;
+	}
+
+	/**
+	 * Generate a list of lines with information about when the lines were
+	 * introduced into the file path.
+	 *
+	 * @return list of lines
+	 */
+	public BlameResult call() throws JGitInternalException {
+		checkCallable();
+		BlameGenerator gen = new BlameGenerator(repo, path);
+		try {
+			if (diffAlgorithm != null)
+				gen.setDiffAlgorithm(diffAlgorithm);
+			if (textComparator != null)
+				gen.setTextComparator(textComparator);
+			if (followFileRenames != null)
+				gen.setFollowFileRenames(followFileRenames.booleanValue());
+
+			if (reverseEndCommits != null)
+				gen.reverse(startCommit, reverseEndCommits);
+			else if (startCommit != null)
+				gen.push(null, startCommit);
+			else {
+				gen.push(null, repo.resolve(Constants.HEAD));
+				if (!repo.isBare()) {
+					DirCache dc = repo.readDirCache();
+					int entry = dc.findEntry(path);
+					if (0 <= entry)
+						gen.push(null, dc.getEntry(entry).getObjectId());
+
+					File inTree = new File(repo.getWorkTree(), path);
+					if (inTree.isFile())
+						gen.push(null, new RawText(inTree));
+				}
+			}
+			return gen.computeBlameResult();
+		} catch (IOException e) {
+			throw new JGitInternalException(e.getMessage(), e);
+		} finally {
+			gen.release();
+		}
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
index 682455077f..4d81e86ef6 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/Git.java
@@ -456,6 +456,19 @@ public class Git {
 	}
 
 	/**
+	 * Returns a command object to execute a {@code blame} command
+	 *
+	 * @see <a
+	 *      href="http://www.kernel.org/pub/software/scm/git/docs/git-blame.html"
+	 *      >Git documentation about Blame</a>
+	 * @return a {@link BlameCommand} used to collect all optional parameters
+	 *         and to finally execute the {@code blame} command
+	 */
+	public BlameCommand blame() {
+		return new BlameCommand(repo);
+	}
+
+	/**
 	 * @return the git repository this class is interacting with
 	 */
 	public Repository getRepository() {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/blame/BlameGenerator.java b/org.eclipse.jgit/src/org/eclipse/jgit/blame/BlameGenerator.java
new file mode 100644
index 0000000000..3b8e41eb16
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/blame/BlameGenerator.java
@@ -0,0 +1,960 @@
+/*
+ * Copyright (C) 2011, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.blame;
+
+import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.Collections;
+
+import org.eclipse.jgit.JGitText;
+import org.eclipse.jgit.blame.Candidate.BlobCandidate;
+import org.eclipse.jgit.blame.Candidate.ReverseCandidate;
+import org.eclipse.jgit.blame.ReverseWalk.ReverseCommit;
+import org.eclipse.jgit.diff.DiffAlgorithm;
+import org.eclipse.jgit.diff.DiffEntry;
+import org.eclipse.jgit.diff.DiffEntry.ChangeType;
+import org.eclipse.jgit.diff.EditList;
+import org.eclipse.jgit.diff.HistogramDiff;
+import org.eclipse.jgit.diff.RawText;
+import org.eclipse.jgit.diff.RawTextComparator;
+import org.eclipse.jgit.diff.RenameDetector;
+import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.MutableObjectId;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectLoader;
+import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.PersonIdent;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevFlag;
+import org.eclipse.jgit.revwalk.RevWalk;
+import org.eclipse.jgit.treewalk.TreeWalk;
+import org.eclipse.jgit.treewalk.filter.PathFilter;
+import org.eclipse.jgit.treewalk.filter.TreeFilter;
+
+/**
+ * Generate author information for lines based on introduction to the file.
+ * <p>
+ * Applications that want a simple one-shot computation of blame for a file
+ * should use {@link #computeBlameResult()} to prepare the entire result in one
+ * method call. This may block for significant time as the history of the
+ * repository must be traversed until information is gathered for every line.
+ * <p>
+ * Applications that want more incremental update behavior may use either the
+ * raw {@link #next()} streaming approach supported by this class, or construct
+ * a {@link BlameResult} using {@link BlameResult#create(BlameGenerator)} and
+ * incrementally construct the result with {@link BlameResult#computeNext()}.
+ * <p>
+ * This class is not thread-safe.
+ * <p>
+ * An instance of BlameGenerator can only be used once. To blame multiple files
+ * the application must create a new BlameGenerator.
+ * <p>
+ * During blame processing there are two files involved:
+ * <ul>
+ * <li>result - The file whose lines are being examined. This is the revision
+ * the user is trying to view blame/annotation information alongside of.</li>
+ * <li>source - The file that was blamed with supplying one or more lines of
+ * data into result. The source may be a different file path (due to copy or
+ * rename). Source line numbers may differ from result line numbers due to lines
+ * being added/removed in intermediate revisions.</li>
+ * </ul>
+ * <p>
+ * The blame algorithm is implemented by initially assigning responsibility for
+ * all lines of the result to the starting commit. A difference against the
+ * commit's ancestor is computed, and responsibility is passed to the ancestor
+ * commit for any lines that are common. The starting commit is blamed only for
+ * the lines that do not appear in the ancestor, if any. The loop repeats using
+ * the ancestor, until there are no more lines to acquire information on, or the
+ * file's creation point is discovered in history.
+ */
+public class BlameGenerator {
+	private final Repository repository;
+
+	private final PathFilter resultPath;
+
+	private final MutableObjectId idBuf;
+
+	/** Revision pool used to acquire commits from. */
+	private RevWalk revPool;
+
+	/** Indicates the commit has already been processed. */
+	private RevFlag SEEN;
+
+	private ObjectReader reader;
+
+	private TreeWalk treeWalk;
+
+	private DiffAlgorithm diffAlgorithm = new HistogramDiff();
+
+	private RawTextComparator textComparator = RawTextComparator.DEFAULT;
+
+	private RenameDetector renameDetector;
+
+	/** Potential candidates, sorted by commit time descending. */
+	private Candidate queue;
+
+	/** Number of lines that still need to be discovered. */
+	private int remaining;
+
+	/** Blame is currently assigned to this source. */
+	private Candidate currentSource;
+
+	/**
+	 * Create a blame generator for the repository and path
+	 *
+	 * @param repository
+	 *            repository to access revision data from.
+	 * @param path
+	 *            initial path of the file to start scanning.
+	 */
+	public BlameGenerator(Repository repository, String path) {
+		this.repository = repository;
+		this.resultPath = PathFilter.create(path);
+
+		idBuf = new MutableObjectId();
+		setFollowFileRenames(true);
+		initRevPool(false);
+
+		remaining = -1;
+	}
+
+	private void initRevPool(boolean reverse) {
+		if (queue != null)
+			throw new IllegalStateException();
+
+		if (revPool != null)
+			revPool.release();
+
+		if (reverse)
+			revPool = new ReverseWalk(getRepository());
+		else
+			revPool = new RevWalk(getRepository());
+
+		revPool.setRetainBody(true);
+		SEEN = revPool.newFlag("SEEN");
+		reader = revPool.getObjectReader();
+		treeWalk = new TreeWalk(reader);
+	}
+
+	/** @return repository being scanned for revision history. */
+	public Repository getRepository() {
+		return repository;
+	}
+
+	/** @return path file path being processed. */
+	public String getResultPath() {
+		return resultPath.getPath();
+	}
+
+	/**
+	 * Difference algorithm to use when comparing revisions.
+	 *
+	 * @param algorithm
+	 * @return {@code this}
+	 */
+	public BlameGenerator setDiffAlgorithm(DiffAlgorithm algorithm) {
+		diffAlgorithm = algorithm;
+		return this;
+	}
+
+	/**
+	 * Text comparator to use when comparing revisions.
+	 *
+	 * @param comparator
+	 * @return {@code this}
+	 */
+	public BlameGenerator setTextComparator(RawTextComparator comparator) {
+		textComparator = comparator;
+		return this;
+	}
+
+	/**
+	 * Enable (or disable) following file renames, on by default.
+	 * <p>
+	 * If true renames are followed using the standard FollowFilter behavior
+	 * used by RevWalk (which matches {@code git log --follow} in the C
+	 * implementation). This is not the same as copy/move detection as
+	 * implemented by the C implementation's of {@code git blame -M -C}.
+	 *
+	 * @param follow
+	 *            enable following.
+	 * @return {@code this}
+	 */
+	public BlameGenerator setFollowFileRenames(boolean follow) {
+		if (follow)
+			renameDetector = new RenameDetector(getRepository());
+		else
+			renameDetector = null;
+		return this;
+	}
+
+	/**
+	 * Obtain the RenameDetector if {@code setFollowFileRenames(true)}.
+	 *
+	 * @return the rename detector, allowing the application to configure its
+	 *         settings for rename score and breaking behavior.
+	 */
+	public RenameDetector getRenameDetector() {
+		return renameDetector;
+	}
+
+	/**
+	 * Push a candidate blob onto the generator's traversal stack.
+	 * <p>
+	 * Candidates should be pushed in history order from oldest-to-newest.
+	 * Applications should push the starting commit first, then the index
+	 * revision (if the index is interesting), and finally the working tree
+	 * copy (if the working tree is interesting).
+	 *
+	 * @param description
+	 *            description of the blob revision, such as "Working Tree".
+	 * @param contents
+	 *            contents of the file.
+	 * @return {@code this}
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public BlameGenerator push(String description, byte[] contents)
+			throws IOException {
+		return push(description, new RawText(contents));
+	}
+
+	/**
+	 * Push a candidate blob onto the generator's traversal stack.
+	 * <p>
+	 * Candidates should be pushed in history order from oldest-to-newest.
+	 * Applications should push the starting commit first, then the index
+	 * revision (if the index is interesting), and finally the working tree copy
+	 * (if the working tree is interesting).
+	 *
+	 * @param description
+	 *            description of the blob revision, such as "Working Tree".
+	 * @param contents
+	 *            contents of the file.
+	 * @return {@code this}
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public BlameGenerator push(String description, RawText contents)
+			throws IOException {
+		if (description == null)
+			description = JGitText.get().blameNotCommittedYet;
+		BlobCandidate c = new BlobCandidate(description, resultPath);
+		c.sourceText = contents;
+		c.regionList = new Region(0, 0, contents.size());
+		remaining = contents.size();
+		push(c);
+		return this;
+	}
+
+	/**
+	 * Push a candidate object onto the generator's traversal stack.
+	 * <p>
+	 * Candidates should be pushed in history order from oldest-to-newest.
+	 * Applications should push the starting commit first, then the index
+	 * revision (if the index is interesting), and finally the working tree copy
+	 * (if the working tree is interesting).
+	 *
+	 * @param description
+	 *            description of the blob revision, such as "Working Tree".
+	 * @param id
+	 *            may be a commit or a blob.
+	 * @return {@code this}
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public BlameGenerator push(String description, AnyObjectId id)
+			throws IOException {
+		ObjectLoader ldr = reader.open(id);
+		if (ldr.getType() == OBJ_BLOB) {
+			if (description == null)
+				description = JGitText.get().blameNotCommittedYet;
+			BlobCandidate c = new BlobCandidate(description, resultPath);
+			c.sourceBlob = id.toObjectId();
+			c.sourceText = new RawText(ldr.getCachedBytes(Integer.MAX_VALUE));
+			c.regionList = new Region(0, 0, c.sourceText.size());
+			remaining = c.sourceText.size();
+			push(c);
+			return this;
+		}
+
+		RevCommit commit = revPool.parseCommit(id);
+		if (!find(commit, resultPath))
+			return this;
+
+		Candidate c = new Candidate(commit, resultPath);
+		c.sourceBlob = idBuf.toObjectId();
+		c.loadText(reader);
+		c.regionList = new Region(0, 0, c.sourceText.size());
+		remaining = c.sourceText.size();
+		push(c);
+		return this;
+	}
+
+	/**
+	 * Configure the generator to compute reverse blame (history of deletes).
+	 * <p>
+	 * This method is expensive as it immediately runs a RevWalk over the
+	 * history spanning the expression {@code start..end} (end being more recent
+	 * than start) and then performs the equivalent operation as
+	 * {@link #push(String, AnyObjectId)} to begin blame traversal from the
+	 * commit named by {@code start} walking forwards through history until
+	 * {@code end} blaming line deletions.
+	 * <p>
+	 * A reverse blame may produce multiple sources for the same result line,
+	 * each of these is a descendant commit that removed the line, typically
+	 * this occurs when the same deletion appears in multiple side branches such
+	 * as due to a cherry-pick. Applications relying on reverse should use
+	 * {@link BlameResult} as it filters these duplicate sources and only
+	 * remembers the first (oldest) deletion.
+	 *
+	 * @param start
+	 *            oldest commit to traverse from. The result file will be loaded
+	 *            from this commit's tree.
+	 * @param end
+	 *            most recent commit to stop traversal at. Usually an active
+	 *            branch tip, tag, or HEAD.
+	 * @return {@code this}
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public BlameGenerator reverse(AnyObjectId start, AnyObjectId end)
+			throws IOException {
+		return reverse(start, Collections.singleton(end.toObjectId()));
+	}
+
+	/**
+	 * Configure the generator to compute reverse blame (history of deletes).
+	 * <p>
+	 * This method is expensive as it immediately runs a RevWalk over the
+	 * history spanning the expression {@code start..end} (end being more recent
+	 * than start) and then performs the equivalent operation as
+	 * {@link #push(String, AnyObjectId)} to begin blame traversal from the
+	 * commit named by {@code start} walking forwards through history until
+	 * {@code end} blaming line deletions.
+	 * <p>
+	 * A reverse blame may produce multiple sources for the same result line,
+	 * each of these is a descendant commit that removed the line, typically
+	 * this occurs when the same deletion appears in multiple side branches such
+	 * as due to a cherry-pick. Applications relying on reverse should use
+	 * {@link BlameResult} as it filters these duplicate sources and only
+	 * remembers the first (oldest) deletion.
+	 *
+	 * @param start
+	 *            oldest commit to traverse from. The result file will be loaded
+	 *            from this commit's tree.
+	 * @param end
+	 *            most recent commits to stop traversal at. Usually an active
+	 *            branch tip, tag, or HEAD.
+	 * @return {@code this}
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public BlameGenerator reverse(AnyObjectId start,
+			Collection<? extends ObjectId> end) throws IOException {
+		initRevPool(true);
+
+		ReverseCommit result = (ReverseCommit) revPool.parseCommit(start);
+		if (!find(result, resultPath))
+			return this;
+
+		revPool.markUninteresting(result);
+		for (ObjectId id : end)
+			revPool.markStart(revPool.parseCommit(id));
+
+		while (revPool.next() != null) {
+			// just pump the queue
+		}
+
+		ReverseCandidate c = new ReverseCandidate(result, resultPath);
+		c.sourceBlob = idBuf.toObjectId();
+		c.loadText(reader);
+		c.regionList = new Region(0, 0, c.sourceText.size());
+		remaining = c.sourceText.size();
+		push(c);
+		return this;
+	}
+
+	/**
+	 * Execute the generator in a blocking fashion until all data is ready.
+	 *
+	 * @return the complete result. Null if no file exists for the given path.
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public BlameResult computeBlameResult() throws IOException {
+		try {
+			BlameResult r = BlameResult.create(this);
+			if (r != null)
+				r.computeAll();
+			return r;
+		} finally {
+			release();
+		}
+	}
+
+	/**
+	 * Step the blame algorithm one iteration.
+	 *
+	 * @return true if the generator has found a region's source. The getSource*
+	 *         and {@link #getResultStart()}, {@link #getResultEnd()} methods
+	 *         can be used to inspect the region found. False if there are no
+	 *         more regions to describe.
+	 * @throws IOException
+	 *             repository cannot be read.
+	 */
+	public boolean next() throws IOException {
+		// If there is a source still pending, produce the next region.
+		if (currentSource != null) {
+			Region r = currentSource.regionList;
+			Region n = r.next;
+			remaining -= r.length;
+			if (n != null) {
+				currentSource.regionList = n;
+				return true;
+			}
+
+			if (currentSource.queueNext != null)
+				return result(currentSource.queueNext);
+
+			currentSource = null;
+		}
+
+		// If there are no lines remaining, the entire result is done,
+		// even if there are revisions still available for the path.
+		if (remaining == 0)
+			return done();
+
+		for (;;) {
+			Candidate n = pop();
+			if (n == null)
+				return done();
+
+			int pCnt = n.getParentCount();
+			if (pCnt == 1) {
+				if (processOne(n))
+					return true;
+
+			} else if (1 < pCnt) {
+				if (processMerge(n))
+					return true;
+
+			} else if (n instanceof ReverseCandidate) {
+				// Do not generate a tip of a reverse. The region
+				// survives and should not appear to be deleted.
+
+			} else /* if (pCnt == 0) */{
+				// Root commit, with at least one surviving region.
+				// Assign the remaining blame here.
+				return result(n);
+			}
+		}
+	}
+
+	private boolean done() {
+		release();
+		return false;
+	}
+
+	private boolean result(Candidate n) throws IOException {
+		if (n.sourceCommit != null)
+			revPool.parseBody(n.sourceCommit);
+		currentSource = n;
+		return true;
+	}
+
+	private boolean reverseResult(Candidate parent, Candidate source)
+			throws IOException {
+		// On a reverse blame present the application the parent
+		// (as this is what did the removals), however the region
+		// list to enumerate is the source's surviving list.
+		Candidate res = parent.copy(parent.sourceCommit);
+		res.regionList = source.regionList;
+		return result(res);
+	}
+
+	private Candidate pop() {
+		Candidate n = queue;
+		if (n != null) {
+			queue = n.queueNext;
+			n.queueNext = null;
+		}
+		return n;
+	}
+
+	private void push(BlobCandidate toInsert) {
+		Candidate c = queue;
+		if (c != null) {
+			c.regionList = null;
+			toInsert.parent = c;
+		}
+		queue = toInsert;
+	}
+
+	private void push(Candidate toInsert) {
+		// Mark sources to ensure they get discarded (above) if
+		// another path to the same commit.
+		toInsert.add(SEEN);
+
+		// Insert into the queue using descending commit time, so
+		// the most recent commit will pop next.
+		int time = toInsert.getTime();
+		Candidate n = queue;
+		if (n == null || time >= n.getTime()) {
+			toInsert.queueNext = n;
+			queue = toInsert;
+			return;
+		}
+
+		for (Candidate p = n;; p = n) {
+			n = p.queueNext;
+			if (n == null || time >= n.getTime()) {
+				toInsert.queueNext = n;
+				p.queueNext = toInsert;
+				return;
+			}
+		}
+	}
+
+	private boolean processOne(Candidate n) throws IOException {
+		RevCommit parent = n.getParent(0);
+		if (parent == null)
+			return split(n.getNextCandidate(0), n);
+		if (parent.has(SEEN))
+			return false;
+		revPool.parseHeaders(parent);
+
+		if (find(parent, n.sourcePath)) {
+			if (idBuf.equals(n.sourceBlob)) {
+				// The common case of the file not being modified in
+				// a simple string-of-pearls history. Blame parent.
+				n.sourceCommit = parent;
+				push(n);
+				return false;
+			}
+
+			Candidate next = n.create(parent, n.sourcePath);
+			next.sourceBlob = idBuf.toObjectId();
+			next.loadText(reader);
+			return split(next, n);
+		}
+
+		if (n.sourceCommit == null)
+			return result(n);
+
+		DiffEntry r = findRename(parent, n.sourceCommit, n.sourcePath);
+		if (r == null)
+			return result(n);
+
+		if (0 == r.getOldId().prefixCompare(n.sourceBlob)) {
+			// A 100% rename without any content change can also
+			// skip directly to the parent.
+			n.sourceCommit = parent;
+			n.sourcePath = PathFilter.create(r.getOldPath());
+			push(n);
+			return false;
+		}
+
+		Candidate next = n.create(parent, PathFilter.create(r.getOldPath()));
+		next.sourceBlob = r.getOldId().toObjectId();
+		next.renameScore = r.getScore();
+		next.loadText(reader);
+		return split(next, n);
+	}
+
+	private boolean split(Candidate parent, Candidate source)
+			throws IOException {
+		EditList editList = diffAlgorithm.diff(textComparator,
+				parent.sourceText, source.sourceText);
+		if (editList.isEmpty()) {
+			// Ignoring whitespace (or some other special comparator) can
+			// cause non-identical blobs to have an empty edit list. In
+			// a case like this push the parent alone.
+			parent.regionList = source.regionList;
+			push(parent);
+			return false;
+		}
+
+		parent.takeBlame(editList, source);
+		if (parent.regionList != null)
+			push(parent);
+		if (source.regionList != null) {
+			if (source instanceof ReverseCandidate)
+				return reverseResult(parent, source);
+			return result(source);
+		}
+		return false;
+	}
+
+	private boolean processMerge(Candidate n) throws IOException {
+		int pCnt = n.getParentCount();
+
+		for (int pIdx = 0; pIdx < pCnt; pIdx++) {
+			RevCommit parent = n.getParent(pIdx);
+			if (parent.has(SEEN))
+				continue;
+			revPool.parseHeaders(parent);
+		}
+
+		// If any single parent exactly matches the merge, follow only
+		// that one parent through history.
+		ObjectId[] ids = null;
+		for (int pIdx = 0; pIdx < pCnt; pIdx++) {
+			RevCommit parent = n.getParent(pIdx);
+			if (parent.has(SEEN))
+				continue;
+			if (!find(parent, n.sourcePath))
+				continue;
+			if (!(n instanceof ReverseCandidate) && idBuf.equals(n.sourceBlob)) {
+				n.sourceCommit = parent;
+				push(n);
+				return false;
+			}
+			if (ids == null)
+				ids = new ObjectId[pCnt];
+			ids[pIdx] = idBuf.toObjectId();
+		}
+
+		// If rename detection is enabled, search for any relevant names.
+		DiffEntry[] renames = null;
+		if (renameDetector != null) {
+			renames = new DiffEntry[pCnt];
+			for (int pIdx = 0; pIdx < pCnt; pIdx++) {
+				RevCommit parent = n.getParent(pIdx);
+				if (parent.has(SEEN))
+					continue;
+				if (ids != null && ids[pIdx] != null)
+					continue;
+
+				DiffEntry r = findRename(parent, n.sourceCommit, n.sourcePath);
+				if (r == null)
+					continue;
+
+				if (n instanceof ReverseCandidate) {
+					if (ids == null)
+						ids = new ObjectId[pCnt];
+					ids[pCnt] = r.getOldId().toObjectId();
+				} else if (0 == r.getOldId().prefixCompare(n.sourceBlob)) {
+					// A 100% rename without any content change can also
+					// skip directly to the parent. Note this bypasses an
+					// earlier parent that had the path (above) but did not
+					// have an exact content match. For performance reasons
+					// we choose to follow the one parent over trying to do
+					// possibly both parents.
+					n.sourceCommit = parent;
+					n.sourcePath = PathFilter.create(r.getOldPath());
+					push(n);
+					return false;
+				}
+
+				renames[pIdx] = r;
+			}
+		}
+
+		// Construct the candidate for each parent.
+		Candidate[] parents = new Candidate[pCnt];
+		for (int pIdx = 0; pIdx < pCnt; pIdx++) {
+			RevCommit parent = n.getParent(pIdx);
+			if (parent.has(SEEN))
+				continue;
+
+			Candidate p;
+			if (renames != null && renames[pIdx] != null) {
+				p = n.create(parent,
+						PathFilter.create(renames[pIdx].getOldPath()));
+				p.renameScore = renames[pIdx].getScore();
+				p.sourceBlob = renames[pIdx].getOldId().toObjectId();
+			} else if (ids != null && ids[pIdx] != null) {
+				p = n.create(parent, n.sourcePath);
+				p.sourceBlob = ids[pIdx];
+			} else {
+				continue;
+			}
+
+			EditList editList;
+			if (n instanceof ReverseCandidate
+					&& p.sourceBlob.equals(n.sourceBlob)) {
+				// This special case happens on ReverseCandidate forks.
+				p.sourceText = n.sourceText;
+				editList = new EditList(0);
+			} else {
+				p.loadText(reader);
+				editList = diffAlgorithm.diff(textComparator,
+						p.sourceText, n.sourceText);
+			}
+
+			if (editList.isEmpty()) {
+				// Ignoring whitespace (or some other special comparator) can
+				// cause non-identical blobs to have an empty edit list. In
+				// a case like this push the parent alone.
+				if (n instanceof ReverseCandidate) {
+					parents[pIdx] = p;
+					continue;
+				}
+
+				p.regionList = n.regionList;
+				push(p);
+				return false;
+			}
+
+			p.takeBlame(editList, n);
+
+			// Only remember this parent candidate if there is at least
+			// one region that was blamed on the parent.
+			if (p.regionList != null) {
+				// Reverse blame requires inverting the regions. This puts
+				// the regions the parent deleted from us into the parent,
+				// and retains the common regions to look at other parents
+				// for deletions.
+				if (n instanceof ReverseCandidate) {
+					Region r = p.regionList;
+					p.regionList = n.regionList;
+					n.regionList = r;
+				}
+
+				parents[pIdx] = p;
+			}
+		}
+
+		if (n instanceof ReverseCandidate) {
+			// On a reverse blame report all deletions found in the children,
+			// and pass on to them a copy of our region list.
+			Candidate resultHead = null;
+			Candidate resultTail = null;
+
+			for (int pIdx = 0; pIdx < pCnt; pIdx++) {
+				Candidate p = parents[pIdx];
+				if (p == null)
+					continue;
+
+				if (p.regionList != null) {
+					Candidate r = p.copy(p.sourceCommit);
+					if (resultTail != null) {
+						resultTail.queueNext = r;
+						resultTail = r;
+					} else {
+						resultHead = r;
+						resultTail = r;
+					}
+				}
+
+				if (n.regionList != null) {
+					p.regionList = n.regionList.deepCopy();
+					push(p);
+				}
+			}
+
+			if (resultHead != null)
+				return result(resultHead);
+			return false;
+		}
+
+		// Push any parents that are still candidates.
+		for (int pIdx = 0; pIdx < pCnt; pIdx++) {
+			if (parents[pIdx] != null)
+				push(parents[pIdx]);
+		}
+
+		if (n.regionList != null)
+			return result(n);
+		return false;
+	}
+
+	/**
+	 * Get the revision blamed for the current region.
+	 * <p>
+	 * The source commit may be null if the line was blamed to an uncommitted
+	 * revision, such as the working tree copy, or during a reverse blame if the
+	 * line survives to the end revision (e.g. the branch tip).
+	 *
+	 * @return current revision being blamed.
+	 */
+	public RevCommit getSourceCommit() {
+		return currentSource.sourceCommit;
+	}
+
+	/** @return current author being blamed. */
+	public PersonIdent getSourceAuthor() {
+		return currentSource.getAuthor();
+	}
+
+	/** @return current committer being blamed. */
+	public PersonIdent getSourceCommitter() {
+		RevCommit c = getSourceCommit();
+		return c != null ? c.getCommitterIdent() : null;
+	}
+
+	/** @return path of the file being blamed. */
+	public String getSourcePath() {
+		return currentSource.sourcePath.getPath();
+	}
+
+	/** @return rename score if a rename occurred in {@link #getSourceCommit}. */
+	public int getRenameScore() {
+		return currentSource.renameScore;
+	}
+
+	/**
+	 * @return first line of the source data that has been blamed for the
+	 *         current region. This is line number of where the region was added
+	 *         during {@link #getSourceCommit()} in file
+	 *         {@link #getSourcePath()}.
+	 */
+	public int getSourceStart() {
+		return currentSource.regionList.sourceStart;
+	}
+
+	/**
+	 * @return one past the range of the source data that has been blamed for
+	 *         the current region. This is line number of where the region was
+	 *         added during {@link #getSourceCommit()} in file
+	 *         {@link #getSourcePath()}.
+	 */
+	public int getSourceEnd() {
+		Region r = currentSource.regionList;
+		return r.sourceStart + r.length;
+	}
+
+	/**
+	 * @return first line of the result that {@link #getSourceCommit()} has been
+	 *         blamed for providing. Line numbers use 0 based indexing.
+	 */
+	public int getResultStart() {
+		return currentSource.regionList.resultStart;
+	}
+
+	/**
+	 * @return one past the range of the result that {@link #getSourceCommit()}
+	 *         has been blamed for providing. Line numbers use 0 based indexing.
+	 *         Because a source cannot be blamed for an empty region of the
+	 *         result, {@link #getResultEnd()} is always at least one larger
+	 *         than {@link #getResultStart()}.
+	 */
+	public int getResultEnd() {
+		Region r = currentSource.regionList;
+		return r.resultStart + r.length;
+	}
+
+	/**
+	 * @return number of lines in the current region being blamed to
+	 *         {@link #getSourceCommit()}. This is always the value of the
+	 *         expression {@code getResultEnd() - getResultStart()}, but also
+	 *         {@code getSourceEnd() - getSourceStart()}.
+	 */
+	public int getRegionLength() {
+		return currentSource.regionList.length;
+	}
+
+	/**
+	 * @return complete contents of the source file blamed for the current
+	 *         output region. This is the contents of {@link #getSourcePath()}
+	 *         within {@link #getSourceCommit()}. The source contents is
+	 *         temporarily available as an artifact of the blame algorithm. Most
+	 *         applications will want the result contents for display to users.
+	 */
+	public RawText getSourceContents() {
+		return currentSource.sourceText;
+	}
+
+	/**
+	 * @return complete file contents of the result file blame is annotating.
+	 *         This value is accessible only after being configured and only
+	 *         immediately before the first call to {@link #next()}. Returns
+	 *         null if the path does not exist.
+	 * @throws IOException
+	 *             repository cannot be read.
+	 * @throws IllegalStateException
+	 *             {@link #next()} has already been invoked.
+	 */
+	public RawText getResultContents() throws IOException {
+		return queue != null ? queue.sourceText : null;
+	}
+
+	/** Release the current blame session. */
+	public void release() {
+		revPool.release();
+		queue = null;
+		currentSource = null;
+	}
+
+	private boolean find(RevCommit commit, PathFilter path) throws IOException {
+		treeWalk.setFilter(path);
+		treeWalk.reset(commit.getTree());
+		while (treeWalk.next()) {
+			if (path.isDone(treeWalk)) {
+				if (treeWalk.getFileMode(0).getObjectType() != OBJ_BLOB)
+					return false;
+				treeWalk.getObjectId(idBuf, 0);
+				return true;
+			}
+
+			if (treeWalk.isSubtree())
+				treeWalk.enterSubtree();
+		}
+		return false;
+	}
+
+	private DiffEntry findRename(RevCommit parent, RevCommit commit,
+			PathFilter path) throws IOException {
+		if (renameDetector == null)
+			return null;
+
+		treeWalk.setFilter(TreeFilter.ANY_DIFF);
+		treeWalk.reset(parent.getTree(), commit.getTree());
+		renameDetector.addAll(DiffEntry.scan(treeWalk));
+		for (DiffEntry ent : renameDetector.compute()) {
+			if (isRename(ent) && ent.getNewPath().equals(path.getPath()))
+				return ent;
+		}
+		return null;
+	}
+
+	private static boolean isRename(DiffEntry ent) {
+		return ent.getChangeType() == ChangeType.RENAME
+				|| ent.getChangeType() == ChangeType.COPY;
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/blame/BlameResult.java b/org.eclipse.jgit/src/org/eclipse/jgit/blame/BlameResult.java
new file mode 100644
index 0000000000..d7a958feeb
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/blame/BlameResult.java
@@ -0,0 +1,356 @@
+/*
+ * Copyright (C) 2011, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.blame;
+
+import java.io.IOException;
+
+import org.eclipse.jgit.diff.RawText;
+import org.eclipse.jgit.lib.PersonIdent;
+import org.eclipse.jgit.revwalk.RevCommit;
+
+/**
+ * Collects line annotations for inspection by applications.
+ * <p>
+ * A result is usually updated incrementally as the BlameGenerator digs back
+ * further through history. Applications that want to lay annotations down text
+ * to the original source file in a viewer may find the BlameResult structure an
+ * easy way to acquire the information, at the expense of keeping tables in
+ * memory tracking every line of the result file.
+ * <p>
+ * This class is not thread-safe.
+ * <p>
+ * During blame processing there are two files involved:
+ * <ul>
+ * <li>result - The file whose lines are being examined. This is the revision
+ * the user is trying to view blame/annotation information alongside of.</li>
+ * <li>source - The file that was blamed with supplying one or more lines of
+ * data into result. The source may be a different file path (due to copy or
+ * rename). Source line numbers may differ from result line numbers due to lines
+ * being added/removed in intermediate revisions.</li>
+ * </ul>
+ */
+public class BlameResult {
+	/**
+	 * Construct a new BlameResult for a generator.
+	 *
+	 * @param gen
+	 *            the generator the result will consume records from.
+	 * @return the new result object. null if the generator cannot find the path
+	 *         it starts from.
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public static BlameResult create(BlameGenerator gen) throws IOException {
+		String path = gen.getResultPath();
+		RawText contents = gen.getResultContents();
+		if (contents == null) {
+			gen.release();
+			return null;
+		}
+		return new BlameResult(gen, path, contents);
+	}
+
+	private final String resultPath;
+
+	private final RevCommit[] sourceCommits;
+
+	private final PersonIdent[] sourceAuthors;
+
+	private final PersonIdent[] sourceCommitters;
+
+	private final String[] sourcePaths;
+
+	/** Warning: these are actually 1-based. */
+	private final int[] sourceLines;
+
+	private RawText resultContents;
+
+	private BlameGenerator generator;
+
+	private int lastLength;
+
+	BlameResult(BlameGenerator bg, String path, RawText text) {
+		generator = bg;
+		resultPath = path;
+		resultContents = text;
+
+		int cnt = text.size();
+		sourceCommits = new RevCommit[cnt];
+		sourceAuthors = new PersonIdent[cnt];
+		sourceCommitters = new PersonIdent[cnt];
+		sourceLines = new int[cnt];
+		sourcePaths = new String[cnt];
+	}
+
+	/** @return path of the file this result annotates. */
+	public String getResultPath() {
+		return resultPath;
+	}
+
+	/** @return contents of the result file, available for display. */
+	public RawText getResultContents() {
+		return resultContents;
+	}
+
+	/** Throw away the {@link #getResultContents()}. */
+	public void discardResultContents() {
+		resultContents = null;
+	}
+
+	/**
+	 * Check if the given result line has been annotated yet.
+	 *
+	 * @param idx
+	 *            line to read data of, 0 based.
+	 * @return true if the data has been annotated, false otherwise.
+	 */
+	public boolean hasSourceData(int idx) {
+		return sourceLines[idx] != 0;
+	}
+
+	/**
+	 * Check if the given result line has been annotated yet.
+	 *
+	 * @param start
+	 *            first index to examine.
+	 * @param end
+	 *            last index to examine.
+	 * @return true if the data has been annotated, false otherwise.
+	 */
+	public boolean hasSourceData(int start, int end) {
+		for (; start < end; start++)
+			if (sourceLines[start] == 0)
+				return false;
+		return true;
+	}
+
+	/**
+	 * Get the commit that provided the specified line of the result.
+	 * <p>
+	 * The source commit may be null if the line was blamed to an uncommitted
+	 * revision, such as the working tree copy, or during a reverse blame if the
+	 * line survives to the end revision (e.g. the branch tip).
+	 *
+	 * @param idx
+	 *            line to read data of, 0 based.
+	 * @return commit that provided line {@code idx}. May be null.
+	 */
+	public RevCommit getSourceCommit(int idx) {
+		return sourceCommits[idx];
+	}
+
+	/**
+	 * Get the author that provided the specified line of the result.
+	 *
+	 * @param idx
+	 *            line to read data of, 0 based.
+	 * @return author that provided line {@code idx}. May be null.
+	 */
+	public PersonIdent getSourceAuthor(int idx) {
+		return sourceAuthors[idx];
+	}
+
+	/**
+	 * Get the committer that provided the specified line of the result.
+	 *
+	 * @param idx
+	 *            line to read data of, 0 based.
+	 * @return committer that provided line {@code idx}. May be null.
+	 */
+	public PersonIdent getSourceCommitter(int idx) {
+		return sourceCommitters[idx];
+	}
+
+	/**
+	 * Get the file path that provided the specified line of the result.
+	 *
+	 * @param idx
+	 *            line to read data of, 0 based.
+	 * @return source file path that provided line {@code idx}.
+	 */
+	public String getSourcePath(int idx) {
+		return sourcePaths[idx];
+	}
+
+	/**
+	 * Get the corresponding line number in the source file.
+	 *
+	 * @param idx
+	 *            line to read data of, 0 based.
+	 * @return matching line number in the source file.
+	 */
+	public int getSourceLine(int idx) {
+		return sourceLines[idx] - 1;
+	}
+
+	/**
+	 * Compute all pending information.
+	 *
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public void computeAll() throws IOException {
+		BlameGenerator gen = generator;
+		if (gen == null)
+			return;
+
+		try {
+			while (gen.next())
+				loadFrom(gen);
+		} finally {
+			gen.release();
+			generator = null;
+		}
+	}
+
+	/**
+	 * Compute the next available segment and return the first index.
+	 * <p>
+	 * Computes one segment and returns to the caller the first index that is
+	 * available. After return the caller can also inspect {@link #lastLength()}
+	 * to determine how many lines of the result were computed.
+	 *
+	 * @return index that is now available. -1 if no more are available.
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public int computeNext() throws IOException {
+		BlameGenerator gen = generator;
+		if (gen == null)
+			return -1;
+
+		if (gen.next()) {
+			loadFrom(gen);
+			lastLength = gen.getRegionLength();
+			return gen.getResultStart();
+		} else {
+			gen.release();
+			generator = null;
+			return -1;
+		}
+	}
+
+	/** @return length of the last segment found by {@link #computeNext()}. */
+	public int lastLength() {
+		return lastLength;
+	}
+
+	/**
+	 * Compute until the entire range has been populated.
+	 *
+	 * @param start
+	 *            first index to examine.
+	 * @param end
+	 *            last index to examine.
+	 * @throws IOException
+	 *             the repository cannot be read.
+	 */
+	public void computeRange(int start, int end) throws IOException {
+		BlameGenerator gen = generator;
+		if (gen == null)
+			return;
+
+		while (start < end) {
+			if (hasSourceData(start, end))
+				return;
+
+			if (!gen.next()) {
+				gen.release();
+				generator = null;
+				return;
+			}
+
+			loadFrom(gen);
+
+			// If the result contains either end of our current range bounds,
+			// update the bounds to avoid scanning that section during the
+			// next loop iteration.
+
+			int resLine = gen.getResultStart();
+			int resEnd = gen.getResultEnd();
+
+			if (resLine <= start && start < resEnd)
+				start = resEnd;
+
+			if (resLine <= end && end < resEnd)
+				end = resLine;
+		}
+	}
+
+	@Override
+	public String toString() {
+		StringBuilder r = new StringBuilder();
+		r.append("BlameResult: ");
+		r.append(getResultPath());
+		return r.toString();
+	}
+
+	private void loadFrom(BlameGenerator gen) {
+		RevCommit srcCommit = gen.getSourceCommit();
+		PersonIdent srcAuthor = gen.getSourceAuthor();
+		PersonIdent srcCommitter = gen.getSourceCommitter();
+		String srcPath = gen.getSourcePath();
+		int srcLine = gen.getSourceStart();
+		int resLine = gen.getResultStart();
+		int resEnd = gen.getResultEnd();
+
+		for (; resLine < resEnd; resLine++) {
+			// Reverse blame can generate multiple results for the same line.
+			// Favor the first one selected, as this is the oldest and most
+			// likely to be nearest to the inquiry made by the user.
+			if (sourceLines[resLine] != 0)
+				continue;
+
+			sourceCommits[resLine] = srcCommit;
+			sourceAuthors[resLine] = srcAuthor;
+			sourceCommitters[resLine] = srcCommitter;
+			sourcePaths[resLine] = srcPath;
+
+			// Since sourceLines is 1-based to permit hasSourceData to use 0 to
+			// mean the line has not been annotated yet, pre-increment instead
+			// of the traditional post-increment when making the assignment.
+			sourceLines[resLine] = ++srcLine;
+		}
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/blame/Candidate.java b/org.eclipse.jgit/src/org/eclipse/jgit/blame/Candidate.java
new file mode 100644
index 0000000000..5f20ce9577
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/blame/Candidate.java
@@ -0,0 +1,386 @@
+/*
+ * Copyright (C) 2011, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.blame;
+
+import java.io.IOException;
+
+import org.eclipse.jgit.blame.ReverseWalk.ReverseCommit;
+import org.eclipse.jgit.diff.Edit;
+import org.eclipse.jgit.diff.EditList;
+import org.eclipse.jgit.diff.RawText;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.ObjectLoader;
+import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.PersonIdent;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevFlag;
+import org.eclipse.jgit.treewalk.filter.PathFilter;
+
+/**
+ * A source that may have supplied some (or all) of the result file.
+ * <p>
+ * Candidates are kept in a queue by BlameGenerator, allowing the generator to
+ * perform a parallel search down the parents of any merges that are discovered
+ * during the history traversal. Each candidate retains a {@link #regionList}
+ * describing sections of the result file the candidate has taken responsibility
+ * for either directly or indirectly through its history. Actual blame from this
+ * region list will be assigned to the candidate when its ancestor commit(s) are
+ * themselves converted into Candidate objects and the ancestor's candidate uses
+ * {@link #takeBlame(EditList, Candidate)} to accept responsibility for sections
+ * of the result.
+ */
+class Candidate {
+	/** Next candidate in the candidate queue. */
+	Candidate queueNext;
+
+	/** Commit being considered (or blamed, depending on state). */
+	RevCommit sourceCommit;
+
+	/** Path of the candidate file in {@link #sourceCommit}. */
+	PathFilter sourcePath;
+
+	/** Unique name of the candidate blob in {@link #sourceCommit}. */
+	ObjectId sourceBlob;
+
+	/** Complete contents of the file in {@link #sourceCommit}. */
+	RawText sourceText;
+
+	/**
+	 * Chain of regions this candidate may be blamed for.
+	 * <p>
+	 * This list is always kept sorted by resultStart order, making it simple to
+	 * merge-join with the sorted EditList during blame assignment.
+	 */
+	Region regionList;
+
+	/**
+	 * Score assigned to the rename to this candidate.
+	 * <p>
+	 * Consider the history "A<-B<-C". If the result file S in C was renamed to
+	 * R in B, the rename score for this rename will be held in this field by
+	 * the candidate object for B. By storing the score with B, the application
+	 * can see what the rename score was as it makes the transition from C/S to
+	 * B/R. This may seem backwards since it was C that performed the rename,
+	 * but the application doesn't learn about path R until B.
+	 */
+	int renameScore;
+
+	Candidate(RevCommit commit, PathFilter path) {
+		sourceCommit = commit;
+		sourcePath = path;
+	}
+
+	int getParentCount() {
+		return sourceCommit.getParentCount();
+	}
+
+	RevCommit getParent(int idx) {
+		return sourceCommit.getParent(idx);
+	}
+
+	Candidate getNextCandidate(@SuppressWarnings("unused") int idx) {
+		return null;
+	}
+
+	void add(RevFlag flag) {
+		sourceCommit.add(flag);
+	}
+
+	int getTime() {
+		return sourceCommit.getCommitTime();
+	}
+
+	PersonIdent getAuthor() {
+		return sourceCommit.getAuthorIdent();
+	}
+
+	Candidate create(RevCommit commit, PathFilter path) {
+		return new Candidate(commit, path);
+	}
+
+	Candidate copy(RevCommit commit) {
+		Candidate r = create(commit, sourcePath);
+		r.sourceBlob = sourceBlob;
+		r.sourceText = sourceText;
+		r.regionList = regionList;
+		r.renameScore = renameScore;
+		return r;
+	}
+
+	void loadText(ObjectReader reader) throws IOException {
+		ObjectLoader ldr = reader.open(sourceBlob, Constants.OBJ_BLOB);
+		sourceText = new RawText(ldr.getCachedBytes(Integer.MAX_VALUE));
+	}
+
+	void takeBlame(EditList editList, Candidate child) {
+		blame(editList, this, child);
+	}
+
+	private static void blame(EditList editList, Candidate a, Candidate b) {
+		Region r = b.clearRegionList();
+		Region aTail = null;
+		Region bTail = null;
+
+		for (int eIdx = 0; eIdx < editList.size();) {
+			// If there are no more regions left, neither side has any
+			// more responsibility for the result. Remaining edits can
+			// be safely ignored.
+			if (r == null)
+				return;
+
+			Edit e = editList.get(eIdx);
+
+			// Edit ends before the next candidate region. Skip the edit.
+			if (e.getEndB() <= r.sourceStart) {
+				eIdx++;
+				continue;
+			}
+
+			// Next candidate region starts before the edit. Assign some
+			// of the blame onto A, but possibly split and also on B.
+			if (r.sourceStart < e.getBeginB()) {
+				int d = e.getBeginB() - r.sourceStart;
+				if (r.length <= d) {
+					// Pass the blame for this region onto A.
+					Region next = r.next;
+					r.sourceStart = e.getBeginA() - d;
+					aTail = add(aTail, a, r);
+					r = next;
+					continue;
+				}
+
+				// Split the region and assign some to A, some to B.
+				aTail = add(aTail, a, r.splitFirst(e.getBeginA() - d, d));
+				r.slideAndShrink(d);
+			}
+
+			// At this point e.getBeginB() <= r.sourceStart.
+
+			// An empty edit on the B side isn't relevant to this split,
+			// as it does not overlap any candidate region.
+			if (e.getLengthB() == 0) {
+				eIdx++;
+				continue;
+			}
+
+			// If the region ends before the edit, blame on B.
+			int rEnd = r.sourceStart + r.length;
+			if (rEnd <= e.getEndB()) {
+				Region next = r.next;
+				bTail = add(bTail, b, r);
+				r = next;
+				if (rEnd == e.getEndB())
+					eIdx++;
+				continue;
+			}
+
+			// This region extends beyond the edit. Blame the first
+			// half of the region on B, and process the rest after.
+			int len = e.getEndB() - r.sourceStart;
+			bTail = add(bTail, b, r.splitFirst(r.sourceStart, len));
+			r.slideAndShrink(len);
+			eIdx++;
+		}
+
+		if (r == null)
+			return;
+
+		// For any remaining region, pass the blame onto A after shifting
+		// the source start to account for the difference between the two.
+		Edit e = editList.get(editList.size() - 1);
+		int endB = e.getEndB();
+		int d = endB - e.getEndA();
+		if (aTail == null)
+			a.regionList = r;
+		else
+			aTail.next = r;
+		do {
+			if (endB <= r.sourceStart)
+				r.sourceStart -= d;
+			r = r.next;
+		} while (r != null);
+	}
+
+	private static Region add(Region aTail, Candidate a, Region n) {
+		// If there is no region on the list, use only this one.
+		if (aTail == null) {
+			a.regionList = n;
+			n.next = null;
+			return n;
+		}
+
+		// If the prior region ends exactly where the new region begins
+		// in both the result and the source, combine these together into
+		// one contiguous region. This occurs when intermediate commits
+		// have inserted and deleted lines in the middle of a region. Try
+		// to report this region as a single region to the application,
+		// rather than in fragments.
+		if (aTail.resultStart + aTail.length == n.resultStart
+				&& aTail.sourceStart + aTail.length == n.sourceStart) {
+			aTail.length += n.length;
+			return aTail;
+		}
+
+		// Append the region onto the end of the list.
+		aTail.next = n;
+		n.next = null;
+		return n;
+	}
+
+	private Region clearRegionList() {
+		Region r = regionList;
+		regionList = null;
+		return r;
+	}
+
+	@Override
+	public String toString() {
+		StringBuilder r = new StringBuilder();
+		r.append("Candidate[");
+		r.append(sourcePath.getPath());
+		if (sourceCommit != null)
+			r.append(" @ ").append(sourceCommit.abbreviate(6).name());
+		if (regionList != null)
+			r.append(" regions:").append(regionList);
+		r.append("]");
+		return r.toString();
+	}
+
+	/**
+	 * Special candidate type used for reverse blame.
+	 * <p>
+	 * Reverse blame inverts the commit history graph to follow from a commit to
+	 * its descendant children, rather than the normal history direction of
+	 * child to parent. These types require a {@link ReverseCommit} which keeps
+	 * children pointers, allowing reverse navigation of history.
+	 */
+	static final class ReverseCandidate extends Candidate {
+		ReverseCandidate(ReverseCommit commit, PathFilter path) {
+			super(commit, path);
+		}
+
+		@Override
+		int getParentCount() {
+			return ((ReverseCommit) sourceCommit).getChildCount();
+		}
+
+		@Override
+		RevCommit getParent(int idx) {
+			return ((ReverseCommit) sourceCommit).getChild(idx);
+		}
+
+		@Override
+		int getTime() {
+			// Invert the timestamp so newer dates sort older.
+			return -sourceCommit.getCommitTime();
+		}
+
+		@Override
+		Candidate create(RevCommit commit, PathFilter path) {
+			return new ReverseCandidate((ReverseCommit) commit, path);
+		}
+
+		@Override
+		public String toString() {
+			return "Reverse" + super.toString();
+		}
+	}
+
+	/**
+	 * Candidate loaded from a file source, and not a commit.
+	 * <p>
+	 * The {@link Candidate#sourceCommit} field is always null on this type of
+	 * candidate. Instead history traversal follows the single {@link #parent}
+	 * field to discover the next Candidate. Often this is a normal Candidate
+	 * type that has a valid sourceCommit.
+	 */
+	static final class BlobCandidate extends Candidate {
+		/**
+		 * Next candidate to pass blame onto.
+		 * <p>
+		 * When computing the differences that this candidate introduced to the
+		 * file content, the parent's sourceText is used as the base.
+		 */
+		Candidate parent;
+
+		/** Author name to refer to this blob with. */
+		String description;
+
+		BlobCandidate(String name, PathFilter path) {
+			super(null, path);
+			description = name;
+		}
+
+		@Override
+		int getParentCount() {
+			return parent != null ? 1 : 0;
+		}
+
+		@Override
+		RevCommit getParent(int idx) {
+			return null;
+		}
+
+		@Override
+		Candidate getNextCandidate(int idx) {
+			return parent;
+		}
+
+		@Override
+		void add(RevFlag flag) {
+			// Do nothing, sourceCommit is null.
+		}
+
+		@Override
+		int getTime() {
+			return Integer.MAX_VALUE;
+		}
+
+		@Override
+		PersonIdent getAuthor() {
+			return new PersonIdent(description, null);
+		}
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/blame/Region.java b/org.eclipse.jgit/src/org/eclipse/jgit/blame/Region.java
new file mode 100644
index 0000000000..9ea346b894
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/blame/Region.java
@@ -0,0 +1,133 @@
+/*
+ * Copyright (C) 2011, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.blame;
+
+/**
+ * Region of the result that still needs to be computed.
+ * <p>
+ * Regions are held in a singly-linked-list by {@link Candidate} using the
+ * {@link Candidate#regionList} field. The list is kept in sorted order by
+ * {@link #resultStart}.
+ */
+class Region {
+	/** Next entry in the region linked list. */
+	Region next;
+
+	/** First position of this region in the result file blame is computing. */
+	int resultStart;
+
+	/** First position in the {@link Candidate} that owns this Region. */
+	int sourceStart;
+
+	/** Length of the region, always >= 1. */
+	int length;
+
+	Region(int rs, int ss, int len) {
+		resultStart = rs;
+		sourceStart = ss;
+		length = len;
+	}
+
+	/**
+	 * Copy the entire result region, but at a new source position.
+	 *
+	 * @param newSource
+	 *            the new source position.
+	 * @return the same result region, but offset for a new source.
+	 */
+	Region copy(int newSource) {
+		return new Region(resultStart, newSource, length);
+	}
+
+	/**
+	 * Split the region, assigning a new source position to the first half.
+	 *
+	 * @param newSource
+	 *            the new source position.
+	 * @param newLen
+	 *            length of the new region.
+	 * @return the first half of the region, at the new source.
+	 */
+	Region splitFirst(int newSource, int newLen) {
+		return new Region(resultStart, newSource, newLen);
+	}
+
+	/**
+	 * Edit this region to remove the first {@code d} elements.
+	 *
+	 * @param d
+	 *            number of elements to remove from the start of this region.
+	 */
+	void slideAndShrink(int d) {
+		resultStart += d;
+		sourceStart += d;
+		length -= d;
+	}
+
+	Region deepCopy() {
+		Region head = new Region(resultStart, sourceStart, length);
+		Region tail = head;
+		for (Region n = next; n != null; n = n.next) {
+			Region q = new Region(n.resultStart, n.sourceStart, n.length);
+			tail.next = q;
+			tail = q;
+		}
+		return head;
+	}
+
+	@Override
+	public String toString() {
+		StringBuilder buf = new StringBuilder();
+		Region r = this;
+		do {
+			if (r != this)
+				buf.append(',');
+			buf.append(r.resultStart);
+			buf.append('-');
+			buf.append(r.resultStart + r.length);
+			r = r.next;
+		} while (r != null);
+		return buf.toString();
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/blame/ReverseWalk.java b/org.eclipse.jgit/src/org/eclipse/jgit/blame/ReverseWalk.java
new file mode 100644
index 0000000000..5b59804cf1
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/blame/ReverseWalk.java
@@ -0,0 +1,113 @@
+/*
+ * Copyright (C) 2011, Google Inc.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.blame;
+
+import java.io.IOException;
+
+import org.eclipse.jgit.errors.IncorrectObjectTypeException;
+import org.eclipse.jgit.errors.MissingObjectException;
+import org.eclipse.jgit.lib.AnyObjectId;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevWalk;
+
+final class ReverseWalk extends RevWalk {
+	ReverseWalk(Repository repo) {
+		super(repo);
+	}
+
+	@Override
+	public ReverseCommit next() throws MissingObjectException,
+			IncorrectObjectTypeException, IOException {
+		ReverseCommit c = (ReverseCommit) super.next();
+		if (c == null)
+			return null;
+		for (int pIdx = 0; pIdx < c.getParentCount(); pIdx++)
+			((ReverseCommit) c.getParent(pIdx)).addChild(c);
+		return c;
+	}
+
+	@Override
+	protected RevCommit createCommit(AnyObjectId id) {
+		return new ReverseCommit(id);
+	}
+
+	static final class ReverseCommit extends RevCommit {
+		private static final ReverseCommit[] NO_CHILDREN = {};
+
+		private ReverseCommit[] children = NO_CHILDREN;
+
+		ReverseCommit(AnyObjectId id) {
+			super(id);
+		}
+
+		void addChild(ReverseCommit c) {
+			// Always put the most recent child onto the front of the list.
+			// This works correctly because our ReverseWalk parent (above)
+			// runs in COMMIT_TIME_DESC order. Older commits will be popped
+			// later and should go in front of the children list so they are
+			// visited first by BlameGenerator when considering candidates.
+
+			int cnt = children.length;
+			if (cnt == 0)
+				children = new ReverseCommit[] { c };
+			else if (cnt == 1)
+				children = new ReverseCommit[] { c, children[0] };
+			else {
+				ReverseCommit[] n = new ReverseCommit[1 + cnt];
+				n[0] = c;
+				System.arraycopy(children, 0, n, 1, cnt);
+				children = n;
+			}
+		}
+
+		int getChildCount() {
+			return children.length;
+		}
+
+		ReverseCommit getChild(final int nth) {
+			return children[nth];
+		}
+	}
+}