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package org.apache.commons.jrcs.diff.myers;
import org.apache.commons.jrcs.diff.*;
import java.util.*;
/**
* A clean-room implementation of
* <a href="http://www.cs.arizona.edu/people/gene/">
* Eugene Myers</a> differencing algorithm.
* <p>
* See the paper at
* <a href="http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps">
* http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps</a>
*
* @version $Revision: 1.6 $ $Date: 2003/05/10 19:47:25 $
* @author <a href="mailto:juanco@suigeneris.org">Juanco Anez</a>
* @see Delta
* @see Revision
* @see Diff
*/
public class MyersDiff
implements DiffAlgorithm
{
private static int MAXTIME = 3000;
public boolean checkMaxTime = false;
/**
* Constructs an instance of the Myers differencing algorithm.
*/
public MyersDiff()
{
}
public void checkMaxTime(boolean checkMaxTime)
{
this.checkMaxTime = checkMaxTime;
}
/**
* {@inheritDoc}
*/
public Revision diff(Object[] orig, Object[] rev)
throws DifferentiationFailedException
{
PathNode path = buildPath(orig, rev);
return buildRevision(path, orig, rev);
}
/**
* Computes the minimum diffpath that expresses de differences
* between the original and revised sequences, according
* to Gene Myers differencing algorithm.
*
* @param orig The original sequence.
* @param rev The revised sequence.
* @return A minimum {@link PathNode Path} accross the differences graph.
* @throws DifferentiationFailedException if a diff path could not be found.
*/
public PathNode buildPath(Object[] orig, Object[] rev)
throws DifferentiationFailedException
{
int N;
int M;
int MAX;
int size;
int middle;
Map<Integer, PathNode> diagonal;
PathNode d_kminus;
PathNode d_kplus;
PathNode path;
PathNode node;
int kmiddle;
int kplus;
int kminus;
PathNode prev;
int i;
int j;
long startTime;
if (orig == null)
{
throw new IllegalArgumentException("original sequence is null");
}
if (rev == null)
{
throw new IllegalArgumentException("revised sequence is null");
}
// these are local constants
N = orig.length;
M = rev.length;
MAX = N + M + 1;
size = 1 + 2 * MAX;
middle = (size + 1) / 2;
diagonal = new HashMap<Integer, PathNode>();
path = null;
startTime = System.currentTimeMillis();
diagonal.put(middle + 1, new Snake(0, -1, null));
for (int d = 0; d < MAX; d++)
{
if (checkMaxTime && System.currentTimeMillis() - startTime > MAXTIME)
{
throw new org.jmeld.diff.MaxTimeExceededException(
"Algoritm is taking up to much time");
}
for (int k = -d; k <= d; k += 2)
{
kmiddle = middle + k;
kplus = kmiddle + 1;
kminus = kmiddle - 1;
prev = null;
d_kminus = diagonal.get(kminus);
d_kplus = diagonal.get(kplus);
if ((k == -d) || (k != d && d_kminus.i < d_kplus.i))
{
i = d_kplus.i;
prev = d_kplus;
}
else
{
i = d_kminus.i + 1;
prev = d_kminus;
}
diagonal.remove(kminus);
j = i - k;
node = new DiffNode(i, j, prev);
// orig and rev are zero-based
// but the algorithm is one-based
// that's why there's no +1 when indexing the sequences
while (i < N && j < M && orig[i].equals(rev[j]))
{
i++;
j++;
}
if (i > node.i)
{
node = new Snake(i, j, node);
}
diagonal.put(kmiddle, node);
if (i >= N && j >= M)
{
return diagonal.get(kmiddle);
}
}
diagonal.put(middle + d - 1, null);
}
// According to Myers, this cannot happen
throw new DifferentiationFailedException("could not find a diff path");
}
private boolean isEmpty(Object o)
{
String s;
if (!(o instanceof String))
{
return false;
}
s = (String) o;
return (s == null || s.trim().compareTo("") == 0);
}
/**
* Constructs a {@link Revision} from a difference path.
*
* @param path The path.
* @param orig The original sequence.
* @param rev The revised sequence.
* @return A {@link Revision} script corresponding to the path.
* @throws DifferentiationFailedException if a {@link Revision} could
* not be built from the given path.
*/
public Revision buildRevision(PathNode path, Object[] orig, Object[] rev)
{
if (path == null)
{
throw new IllegalArgumentException("path is null");
}
if (orig == null)
{
throw new IllegalArgumentException("original sequence is null");
}
if (rev == null)
{
throw new IllegalArgumentException("revised sequence is null");
}
Revision revision = new Revision();
if (path.isSnake())
{
path = path.prev;
}
while (path != null && path.prev != null && path.prev.j >= 0)
{
if (path.isSnake())
{
throw new IllegalStateException(
"bad diffpath: found snake when looking for diff");
}
int i = path.i;
int j = path.j;
path = path.prev;
int ianchor = path.i;
int janchor = path.j;
Delta delta = Delta.newDelta(new Chunk(orig, ianchor, i - ianchor),
new Chunk(rev, janchor, j - janchor));
revision.insertDelta(delta);
if (path.isSnake())
{
path = path.prev;
}
}
return revision;
}
}