222 lines
7.7 KiB
Java
222 lines
7.7 KiB
Java
/*
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* ====================================================================
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*
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* The Apache Software License, Version 1.1
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*
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* Copyright (c) 1999-2003 The Apache Software Foundation. All rights
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* reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* 3. The end-user documentation included with the redistribution, if
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* any, must include the following acknowlegement:
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* "This product includes software developed by the
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* Apache Software Foundation (http://www.apache.org/)."
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* Alternately, this acknowlegement may appear in the software itself,
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* if and wherever such third-party acknowlegements normally appear.
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*
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* 4. The names "The Jakarta Project", "Commons", and "Apache Software
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* Foundation" must not be used to endorse or promote products derived
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* from this software without prior written permission. For written
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* permission, please contact apache@apache.org.
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*
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* 5. Products derived from this software may not be called "Apache"
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* nor may "Apache" appear in their names without prior written
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* permission of the Apache Group.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
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* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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* ====================================================================
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*
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* This software consists of voluntary contributions made by many
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* individuals on behalf of the Apache Software Foundation. For more
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* information on the Apache Software Foundation, please see
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* <http://www.apache.org/>.
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*
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*/
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package org.apache.commons.jrcs.diff.myers;
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import org.apache.commons.jrcs.diff.*;
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/**
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* A clean-room implementation of
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* <a href="http://www.cs.arizona.edu/people/gene/">
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* Eugene Myers</a> differencing algorithm.
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* <p>
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* See the paper at
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* <a href="http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps">
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* http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps</a>
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*
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* @version $Revision: 1.1 $ $Date: 2003/07/14 12:22:30 $
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* @author <a href="mailto:juanco@suigeneris.org">Juanco Anez</a>
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* @see Delta
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* @see Revision
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* @see Diff
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*/
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public class MyersDiff
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implements DiffAlgorithm
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{
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/**
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* Constructs an instance of the Myers differencing algorithm.
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*/
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public MyersDiff()
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{
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}
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/**
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* {@inheritDoc}
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*/
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public Revision diff(Object[] orig, Object[] rev)
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throws DifferentiationFailedException
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{
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PathNode path = buildPath(orig, rev);
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return buildRevision(path, orig, rev);
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}
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/**
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* Computes the minimum diffpath that expresses de differences
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* between the original and revised sequences, according
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* to Gene Myers differencing algorithm.
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*
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* @param orig The original sequence.
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* @param rev The revised sequence.
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* @return A minimum {@link PathNode Path} accross the differences graph.
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* @throws DifferentiationFailedException if a diff path could not be found.
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*/
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public static PathNode buildPath(Object[] orig, Object[] rev)
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throws DifferentiationFailedException
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{
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if (orig == null)
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throw new IllegalArgumentException("original sequence is null");
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if (rev == null)
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throw new IllegalArgumentException("revised sequence is null");
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// these are local constants
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final int N = orig.length;
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final int M = rev.length;
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final int MAX = N + M + 1;
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final int size = 1 + 2 * MAX;
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final int middle = (size + 1) / 2;
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final PathNode diagonal[] = new PathNode[size];
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PathNode path = null;
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diagonal[middle + 1] = new Snake(0, -1, null);
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for (int d = 0; d < MAX; d++)
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{
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for (int k = -d; k <= d; k += 2)
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{
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final int kmiddle = middle + k;
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final int kplus = kmiddle + 1;
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final int kminus = kmiddle - 1;
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PathNode prev = null;
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int i;
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if ( (k == -d) ||
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(k != d && diagonal[kminus].i < diagonal[kplus].i))
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{
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i = diagonal[kplus].i;
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prev = diagonal[kplus];
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}
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else
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{
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i = diagonal[kminus].i + 1;
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prev = diagonal[kminus];
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}
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diagonal[kminus] = null; // no longer used
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int j = i - k;
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PathNode node = new DiffNode(i, j, prev);
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// orig and rev are zero-based
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// but the algorithm is one-based
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// that's why there's no +1 when indexing the sequences
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while (i < N && j < M && orig[i].equals(rev[j]))
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{
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i++;
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j++;
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}
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if (i > node.i)
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node = new Snake(i, j, node);
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diagonal[kmiddle] = node;
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if (i >= N && j >= M)
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{
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return diagonal[kmiddle];
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}
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}
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diagonal[middle+d-1] = null;
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}
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// According to Myers, this cannot happen
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throw new DifferentiationFailedException("could not find a diff path");
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}
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/**
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* Constructs a {@link Revision} from a difference path.
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*
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* @param path The path.
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* @param orig The original sequence.
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* @param rev The revised sequence.
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* @return A {@link Revision} script corresponding to the path.
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* @throws DifferentiationFailedException if a {@link Revision} could
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* not be built from the given path.
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*/
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public static Revision buildRevision(PathNode path, Object[] orig, Object[] rev)
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{
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if (path == null)
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throw new IllegalArgumentException("path is null");
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if (orig == null)
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throw new IllegalArgumentException("original sequence is null");
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if (rev == null)
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throw new IllegalArgumentException("revised sequence is null");
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Revision revision = new Revision();
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if (path.isSnake())
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path = path.prev;
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while (path != null && path.prev != null && path.prev.j >= 0)
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{
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if(path.isSnake())
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throw new IllegalStateException("bad diffpath: found snake when looking for diff");
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int i = path.i;
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int j = path.j;
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path = path.prev;
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int ianchor = path.i;
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int janchor = path.j;
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Delta delta = Delta.newDelta(new Chunk(orig, ianchor, i - ianchor),
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new Chunk(rev, janchor, j - janchor));
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revision.insertDelta(delta);
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if (path.isSnake())
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path = path.prev;
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}
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return revision;
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}
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}
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