/*******************************************************************************
* Copyright (c) 2006 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.compare.rangedifferencer;
import java.util.ArrayList;
/**
* The algorithm used is an objectified version of one described in: <it>A File
* Comparison Program,</it> by Webb Miller and Eugene W. Myers, Software
* Practice and Experience, Vol. 15, Nov. 1985.
*/
/* package */class OldDifferencer {
private static final RangeDifference[] EMPTY_RESULT = new RangeDifference[0];
private static class LinkedRangeDifference extends RangeDifference {
static final int INSERT = 0;
static final int DELETE = 1;
LinkedRangeDifference fNext;
/*
* Creates a LinkedRangeDifference an initializes it to the error state
*/
LinkedRangeDifference() {
super(ERROR);
fNext = null;
}
/*
* Constructs and links a LinkeRangeDifference to another
* LinkedRangeDifference
*/
LinkedRangeDifference(LinkedRangeDifference next, int operation) {
super(operation);
fNext = next;
}
/*
* Follows the next link
*/
LinkedRangeDifference getNext() {
return fNext;
}
boolean isDelete() {
return kind() == DELETE;
}
boolean isInsert() {
return kind() == INSERT;
}
/*
* Sets the next link of this LinkedRangeDifference
*/
void setNext(LinkedRangeDifference next) {
fNext = next;
}
}
public static RangeDifference[] findDifferences(IRangeComparator left, IRangeComparator right) {
// assert that both IRangeComparators are of the same class
// Assert.isTrue(right.getClass().equals(left.getClass()));
int rightSize = right.getRangeCount();
int leftSize = left.getRangeCount();
//
// Differences matrix:
// only the last d of each diagonal is stored, i.e., lastDiagonal[k] =
// row of d
//
int diagLen = 2 * Math.max(rightSize, leftSize); // bound on the size
// of edit script
int maxDiagonal = diagLen;
int lastDiagonal[] = new int[diagLen + 1]; // the row containing the
// last d
// on diagonal k (lastDiagonal[k] = row)
int origin = diagLen / 2; // origin of diagonal 0
// script corresponding to d[k]
LinkedRangeDifference script[] = new LinkedRangeDifference[diagLen + 1];
int row, col;
// find common prefix
for (row = 0; row < rightSize && row < leftSize
&& rangesEqual(right, row, left, row) == true;)
row++;
lastDiagonal[origin] = row;
script[origin] = null;
int lower = (row == rightSize) ? origin + 1 : origin - 1;
int upper = (row == leftSize) ? origin - 1 : origin + 1;
if (lower > upper)
return EMPTY_RESULT;
// System.out.println("findDifferences: " + maxDiagonal + " " + lower +
// " " + upper);
// for each value of the edit distance
for (int d = 1; d <= maxDiagonal; ++d) { // d is the current edit
// distance
if (right.skipRangeComparison(d, maxDiagonal, left))
return EMPTY_RESULT; // should be something we already found
// for each relevant diagonal (-d, -d+2 ..., d-2, d)
for (int k = lower; k <= upper; k += 2) { // k is the current
// diagonal
LinkedRangeDifference edit;
if (k == origin - d || k != origin + d
&& lastDiagonal[k + 1] >= lastDiagonal[k - 1]) {
//
// move down
//
row = lastDiagonal[k + 1] + 1;
edit = new LinkedRangeDifference(script[k + 1],
LinkedRangeDifference.DELETE);
} else {
//
// move right
//
row = lastDiagonal[k - 1];
edit = new LinkedRangeDifference(script[k - 1],
LinkedRangeDifference.INSERT);
}
col = row + k - origin;
edit.fRightStart = row;
edit.fLeftStart = col;
// Assert.isTrue(k >= 0 && k <= maxDiagonal);
script[k] = edit;
// slide down the diagonal as far as possible
while (row < rightSize && col < leftSize
&& rangesEqual(right, row, left, col) == true) {
++row;
++col;
}
// Assert.isTrue(k >= 0 && k <= maxDiagonal); // Unreasonable
// value for
// diagonal index
lastDiagonal[k] = row;
if (row == rightSize && col == leftSize) {
// showScript(script[k], right, left);
return createDifferencesRanges(script[k]);
}
if (row == rightSize)
lower = k + 2;
if (col == leftSize)
upper = k - 2;
}
--lower;
++upper;
}
// too many differences
// Assert.isTrue(false);
return null;
}
/*
* Tests if two ranges are equal
*/
private static boolean rangesEqual(IRangeComparator a, int ai,
IRangeComparator b, int bi) {
return a.rangesEqual(ai, b, bi);
}
/*
* Creates a Vector of DifferencesRanges out of the LinkedRangeDifference.
* It coalesces adjacent changes. In addition, indices are changed such that
* the ranges are 1) open, i.e, the end of the range is not included, and 2)
* are zero based.
*/
private static RangeDifference[] createDifferencesRanges(
LinkedRangeDifference start) {
LinkedRangeDifference ep = reverseDifferences(start);
ArrayList result = new ArrayList();
RangeDifference es = null;
while (ep != null) {
es = new RangeDifference(RangeDifference.CHANGE);
if (ep.isInsert()) {
es.fRightStart = ep.fRightStart + 1;
es.fLeftStart = ep.fLeftStart;
RangeDifference b = ep;
do {
ep = ep.getNext();
es.fLeftLength++;
} while (ep != null && ep.isInsert()
&& ep.fRightStart == b.fRightStart);
} else {
es.fRightStart = ep.fRightStart;
es.fLeftStart = ep.fLeftStart;
RangeDifference a = ep;
//
// deleted lines
//
do {
a = ep;
ep = ep.getNext();
es.fRightLength++;
} while (ep != null && ep.isDelete()
&& ep.fRightStart == a.fRightStart + 1);
boolean change = (ep != null && ep.isInsert() && ep.fRightStart == a.fRightStart);
if (change) {
RangeDifference b = ep;
//
// replacement lines
//
do {
ep = ep.getNext();
es.fLeftLength++;
} while (ep != null && ep.isInsert()
&& ep.fRightStart == b.fRightStart);
} else {
es.fLeftLength = 0;
}
es.fLeftStart++; // meaning of range changes from "insert
// after", to "replace with"
}
//
// the script commands are 1 based, subtract one to make them zero
// based
//
es.fRightStart--;
es.fLeftStart--;
result.add(es);
}
return (RangeDifference[]) result.toArray(EMPTY_RESULT);
}
/*
* Reverses the range differences
*/
private static LinkedRangeDifference reverseDifferences(
LinkedRangeDifference start) {
LinkedRangeDifference ep, behind, ahead;
ahead = start;
ep = null;
while (ahead != null) {
behind = ep;
ep = ahead;
ahead = ahead.getNext();
ep.setNext(behind);
}
return ep;
}
}