diff_match_patch.java

/*
 * Diff Match and Patch
 *
 * Copyright 2006 Google Inc.
 * http://code.google.com/p/google-diff-match-patch/
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 */

import java.util.Arrays;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.util.HashMap;
import java.util.Set;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Stack;
import java.util.ListIterator;
import java.util.regex.*;
import java.net.URLEncoder;
import java.net.URLDecoder;
import java.io.UnsupportedEncodingException;

/*
 * Functions for diff, match and patch.
 * Computes the difference between two texts to create a patch.
 * Applies the patch onto another text, allowing for errors.
 *
 * @author fraser@google.com (Neil Fraser)
 */

/**
 * Class containing the diff, match and patch methods.
 * Also contains the behaviour settings.
 */
public class diff_match_patch {

  // Defaults.
  // Set these on your diff_match_patch instance to override the defaults.

  // Number of seconds to map a diff before giving up.  (0 for infinity)
  public float Diff_Timeout = 1.0f;
  // Cost of an empty edit operation in terms of edit characters.
  public short Diff_EditCost = 4;
  // The size beyond which the double-ended diff activates.
  // Double-ending is twice as fast, but less accurate.
  public short Diff_DualThreshold = 32;
  // Tweak the relative importance (0.0 = accuracy, 1.0 = proximity)
  public float Match_Balance = 0.5f;
  // At what point is no match declared (0.0 = perfection, 1.0 = very loose)
  public float Match_Threshold = 0.5f;
  // The min and max cutoffs used when computing text lengths.
  public int Match_MinLength = 100;
  public int Match_MaxLength = 1000;
  // Chunk size for context length.
  public short Patch_Margin = 4;

  // The number of bits in an int.
  private int Match_MaxBits = 32;


  //  DIFF FUNCTIONS


  /**-
   * The data structure representing a diff is a Linked list of Diff objects:
   * {Diff(Operation.DELETE, "Hello"), Diff(Operation.INSERT, "Goodbye"),
   *  Diff(Operation.EQUAL, " world.")}
   * which means: delete "Hello", add "Goodbye" and keep " world."
   */
  public enum Operation {
    DELETE, INSERT, EQUAL
  }


  /**
   * Find the differences between two texts.
   * Run a faster slightly less optimal diff
   * This method allows the 'checklines' of diff_main() to be optional.
   * Most of the time checklines is wanted, so default to true.
   * @param text1 Old string to be diffed
   * @param text2 New string to be diffed
   * @return Linked List of Diff objects
   */
  public LinkedList<Diff> diff_main(String text1, String text2) {
    return diff_main(text1, text2, true);
  }

  /**
   * Find the differences between two texts.  Simplifies the problem by
   * stripping any common prefix or suffix off the texts before diffing.
   * @param text1 Old string to be diffed
   * @param text2 New string to be diffed
   * @param checklines Speedup flag.  If false, then don't run a
   *     line-level diff first to identify the changed areas.
   *     If true, then run a faster slightly less optimal diff
   * @return Linked List of Diff objects
   */
  public LinkedList<Diff> diff_main(String text1, String text2,
                                    boolean checklines) {
    // Check for equality (speedup)
    LinkedList<Diff> diffs;
    if (text1.equals(text2)) {
      diffs = new LinkedList<Diff>();
      diffs.add(new Diff(Operation.EQUAL, text1));
      return diffs;
    }

    // Trim off common prefix (speedup)
    int commonlength = diff_commonPrefix(text1, text2);
    String commonprefix = text1.substring(0, commonlength);
    text1 = text1.substring(commonlength);
    text2 = text2.substring(commonlength);

    // Trim off common suffix (speedup)
    commonlength = diff_commonSuffix(text1, text2);
    String commonsuffix = text1.substring(text1.length() - commonlength);
    text1 = text1.substring(0, text1.length() - commonlength);
    text2 = text2.substring(0, text2.length() - commonlength);

    // Compute the diff on the middle block
    diffs = diff_compute(text1, text2, checklines);

    // Restore the prefix and suffix
    if (commonprefix.length() != 0) {
      diffs.addFirst(new Diff(Operation.EQUAL, commonprefix));
    }
    if (commonsuffix.length() != 0) {
      diffs.addLast(new Diff(Operation.EQUAL, commonsuffix));
    }

    diff_cleanupMerge(diffs);
    return diffs;
  }


  /**
   * Find the differences between two texts.
   * @param text1 Old string to be diffed
   * @param text2 New string to be diffed
   * @param checklines Speedup flag.  If false, then don't run a
   *     line-level diff first to identify the changed areas.
   *     If true, then run a faster slightly less optimal diff
   * @return Linked List of Diff objects
   */
  public LinkedList<Diff> diff_compute(String text1, String text2,
                                    boolean checklines) {
    LinkedList<Diff> diffs = new LinkedList<Diff>();

    if (text1.length() == 0) {
      // Just add some text (speedup)
      diffs.add(new Diff(Operation.INSERT, text2));
      return diffs;
    }

    if (text2.length() == 0) {
      // Just delete some text (speedup)
      diffs.add(new Diff(Operation.DELETE, text1));
      return diffs;
    }

    String longtext = text1.length() > text2.length() ? text1 : text2;
    String shorttext = text1.length() > text2.length() ? text2 : text1;
    int i = longtext.indexOf(shorttext);
    if (i != -1) {
      // Shorter text is inside the longer text (speedup)
      Operation op = (text1.length() > text2.length()) ?
                     Operation.DELETE : Operation.INSERT;
      diffs.add(new Diff(op, longtext.substring(0, i)));
      diffs.add(new Diff(Operation.EQUAL, shorttext));
      diffs.add(new Diff(op, longtext.substring(i + shorttext.length())));
      return diffs;
    }
    longtext = shorttext = null;  // Garbage collect

    // Check to see if the problem can be split in two.
    String[] hm = diff_halfMatch(text1, text2);
    if (hm != null) {
      // A half-match was found, sort out the return data.
      String text1_a = hm[0];
      String text1_b = hm[1];
      String text2_a = hm[2];
      String text2_b = hm[3];
      String mid_common = hm[4];
      // Send both pairs off for separate processing.
      LinkedList<Diff> diffs_a = diff_main(text1_a, text2_a, checklines);
      LinkedList<Diff> diffs_b = diff_main(text1_b, text2_b, checklines);
      // Merge the results.
      diffs = diffs_a;
      diffs.add(new Diff(Operation.EQUAL, mid_common));
      diffs.addAll(diffs_b);
      return diffs;
    }

    // Perform a real diff.
    if (checklines && text1.length() + text2.length() < 250) {
      checklines = false;  // Too trivial for the overhead.
    }
    ArrayList<String> linearray = null;
    if (checklines) {
      // Scan the text on a line-by-line basis first.
      Object b[] = diff_linesToChars(text1, text2);
      text1 = (String) b[0];
      text2 = (String) b[1];
      linearray = (ArrayList<String>) b[2];
     }

    diffs = diff_map(text1, text2);
    if (diffs == null) {
      // No acceptable result.
      diffs = new LinkedList<Diff>();
      diffs.add(new Diff(Operation.DELETE, text1));
      diffs.add(new Diff(Operation.INSERT, text2));
    }

    if (checklines) {
      // Convert the diff back to original text.
      diff_charsToLines(diffs, linearray);
      // Eliminate freak matches (e.g. blank lines)
      diff_cleanupSemantic(diffs);

      // Rediff any replacement blocks, this time character-by-character.
      // Add a dummy entry at the end.
      diffs.add(new Diff(Operation.EQUAL, ""));
      int count_delete = 0;
      int count_insert = 0;
      String text_delete = "";
      String text_insert = "";
      ListIterator<Diff> pointer = diffs.listIterator();
      Diff thisDiff = pointer.next();
      while (thisDiff != null) {
        if (thisDiff.operation == Operation.INSERT) {
          count_insert++;
          text_insert += thisDiff.text;
        } else if (thisDiff.operation == Operation.DELETE) {
          count_delete++;
          text_delete += thisDiff.text;
        } else {
          // Upon reaching an equality, check for prior redundancies.
          if (count_delete >= 1 && count_insert >= 1) {
            // Delete the offending records and add the merged ones.
            pointer.previous();
            for (int j = 0; j < count_delete + count_insert; j++) {
              pointer.previous();
              pointer.remove();
            }
            for (Diff newDiff : diff_main(text_delete, text_insert, false)) {
              pointer.add(newDiff);
            }
          }
          count_insert = 0;
          count_delete = 0;
          text_delete = "";
          text_insert = "";
        }
        thisDiff = pointer.hasNext() ? pointer.next() : null;
      }
      diffs.removeLast();  // Remove the dummy entry at the end.
    }
    return diffs;
  }


  /**
   * Split two texts into a list of strings.  Reduce the texts to a string of
   * hashes where each Unicode character represents one line.
   * @param text1 First string
   * @param text2 Second string
   * @return Three element Object array, containing the encoded text1, the
   *     encoded text2 and the List of unique strings.  The zeroth element
   *     of the List of unique strings is intentionally blank.
   */
  protected Object[] diff_linesToChars(String text1, String text2) {
    List<String> linearray = new ArrayList<String>();
    Map<String, Integer> linehash = new HashMap<String, Integer>();
    // e.g. linearray[4] == "Hello\n"
    // e.g. linehash.get("Hello\n") == 4

    // "\x00" is a valid character, but various debuggers don't like it.
    // So we'll insert a junk entry to avoid generating a null character.
    linearray.add("");

    String chars1 = diff_linesToCharsMunge(text1, linearray, linehash);
    String chars2 = diff_linesToCharsMunge(text2, linearray, linehash);
    return new Object[]{chars1, chars2, linearray};
  }


  /**
   * Split a text into a list of strings.  Reduce the texts to a string of
   * hashes where each Unicode character represents one line.
   * @param text String to encode
   * @param linearray List of unique strings
   * @param linehash Map of strings to indices
   * @return Encoded string
   */
  private String diff_linesToCharsMunge(String text, List<String> linearray,
                                        Map<String, Integer> linehash) {
    int i;
    String line;
    String chars = "";
    // text.split('\n') would work fine, but would temporarily double our
    // memory footprint for minimal speed improvement.
    while (text.length() != 0) {
      i = text.indexOf('\n');
      if (i == -1) {
        i = text.length() - 1;
      }
      line = text.substring(0, i + 1);
      text = text.substring(i + 1);
      if (linehash.containsKey(line)) {
        chars += String.valueOf((char) (int) linehash.get(line));
      } else {
        linearray.add(line);
        linehash.put(line, linearray.size() - 1);
        chars += String.valueOf((char) (linearray.size() - 1));
      }
    }
    return chars;
  }


  /**
   * Rehydrate the text in a diff from a string of line hashes to real lines of
   * text.
   * @param diffs LinkedList of Diff objects
   * @param linearray List of unique strings
   */
  protected void diff_charsToLines(LinkedList<Diff> diffs,
                                  List<String> linearray) {
    StringBuilder text;
    for (Diff diff : diffs) {
      text = new StringBuilder();
      for (int y = 0; y < diff.text.length(); y++) {
        text.append(linearray.get(diff.text.charAt(y)));
      }
      diff.text = text.toString();
    }
  }

  
  /**
   * Explore the intersection points between the two texts.
   * @param text1 Old string to be diffed
   * @param text2 New string to be diffed
   * @return LinkedList of Diff objects or null if no diff available
   */
  protected LinkedList<Diff> diff_map(String text1, String text2) {
    long ms_end = System.currentTimeMillis() + (long) (Diff_Timeout * 1000);
    int max_d = text1.length() + text2.length() - 1;
    boolean doubleEnd = Diff_DualThreshold * 2 < max_d;
    List<Set<String>> v_map1 = new ArrayList<Set<String>>();
    List<Set<String>> v_map2 = new ArrayList<Set<String>>();
    Map<Integer, Integer> v1 = new HashMap<Integer, Integer>();
    Map<Integer, Integer> v2 = new HashMap<Integer, Integer>();
    v1.put(1, 0);
    v2.put(1, 0);
    int x, y;
    String footstep = "";  // Used to track overlapping paths.
    Map<String, Integer> footsteps = new HashMap<String, Integer>();
    boolean done = false;
    // If the total number of characters is odd, then the front path will
    // collide with the reverse path.
    boolean front = ((text1.length() + text2.length()) % 2 == 1);
    for (int d = 0; d < max_d; d++) {
      // Bail out if timeout reached.
      if (Diff_Timeout > 0 && System.currentTimeMillis() > ms_end) {
        return null;
      }

      // Walk the front path one step.
      v_map1.add(new HashSet<String>());  // Adds at index 'd'.
      for (int k = -d; k <= d; k += 2) {
        if (k == -d || k != d && v1.get(k - 1) < v1.get(k + 1)) {
          x = v1.get(k + 1);
        } else {
          x = v1.get(k - 1) + 1;
        }
        y = x - k;
        if (doubleEnd) {
          footstep = x + "," + y;
          if (front && (footsteps.containsKey(footstep))) {
            done = true;
          }
          if (!front) {
            footsteps.put(footstep, d);
          }
        }
        while (!done && x < text1.length() && y < text2.length()
               && text1.charAt(x) == text2.charAt(y)) {
          x++;
          y++;
          if (doubleEnd) {
            footstep = x + "," + y;
            if (front && (footsteps.containsKey(footstep))) {
              done = true;
            }
            if (!front) {
              footsteps.put(footstep, d);
            }
          }
        }
        v1.put(k, x);
        v_map1.get(d).add(x + "," + y);
        if (x == text1.length() && y == text2.length()) {
          // Reached the end in single-path mode.
          return diff_path1(v_map1, text1, text2);
        } else if (done) {
          // Front path ran over reverse path.
          v_map2 = v_map2.subList(0, footsteps.get(footstep) + 1);
          LinkedList<Diff> a = diff_path1(v_map1, text1.substring(0, x),
                                          text2.substring(0, y));
          a.addAll(diff_path2(v_map2, text1.substring(x), text2.substring(y)));
          return a;
        }
      }

      if (doubleEnd) {
        // Walk the reverse path one step.
        v_map2.add(new HashSet<String>());  // Adds at index 'd'.
        for (int k = -d; k <= d; k += 2) {
          if (k == -d || k != d && v2.get(k - 1) < v2.get(k + 1)) {
            x = v2.get(k + 1);
          } else {
            x = v2.get(k - 1) + 1;
          }
          y = x - k;
          footstep = (text1.length() - x) + "," + (text2.length() - y);
          if (!front && (footsteps.containsKey(footstep))) {
            done = true;
          }
          if (front) {
            footsteps.put(footstep, d);
          }
          while (!done && x < text1.length() && y < text2.length()
                 && text1.charAt(text1.length() - x - 1)
                 == text2.charAt(text2.length() - y - 1)) {
            x++;
            y++;
            footstep = (text1.length() - x) + "," + (text2.length() - y);
            if (!front && (footsteps.containsKey(footstep))) {
              done = true;
            }
            if (front) {
              footsteps.put(footstep, d);
            }
          }
          v2.put(k, x);
          v_map2.get(d).add(x + "," + y);
          if (done) {
            // Reverse path ran over front path.
            v_map1 = v_map1.subList(0, footsteps.get(footstep) + 1);
            LinkedList<Diff> a
                = diff_path1(v_map1, text1.substring(0, text1.length() - x),
                             text2.substring(0, text2.length() - y));
            a.addAll(diff_path2(v_map2, text1.substring(text1.length() - x),
                                text2.substring(text2.length() - y)));
            return a;
          }
        }
      }
    }
    // Number of diffs equals number of characters, no commonality at all.
    return null;
  }


  /**
   * Work from the middle back to the start to determine the path.
   * @param v_map List of path sets.
   * @param text1 Old string fragment to be diffed
   * @param text2 New string fragment to be diffed
   * @return LinkedList of Diff objects
   */
  protected LinkedList<Diff> diff_path1(List<Set<String>> v_map,
                                        String text1, String text2) {
    LinkedList<Diff> path = new LinkedList<Diff>();
    int x = text1.length();
    int y = text2.length();
    Operation last_op = null;
    for (int d = v_map.size() - 2; d >= 0; d--) {
      while (true) {
        if (v_map.get(d).contains((x - 1) + "," + y)) {
          x--;
          if (last_op == Operation.DELETE) {
            path.getFirst().text = text1.charAt(x) + path.getFirst().text;
          } else {
            path.addFirst(new Diff(Operation.DELETE,
                                   text1.substring(x, x + 1)));
          }
          last_op = Operation.DELETE;
          break;
        } else if (v_map.get(d).contains(x + "," + (y - 1))) {
          y--;
          if (last_op == Operation.INSERT) {
            path.getFirst().text = text2.charAt(y) + path.getFirst().text;
          } else {
            path.addFirst(new Diff(Operation.INSERT,
                                   text2.substring(y, y + 1)));
          }
          last_op = Operation.INSERT;
          break;
        } else {
          x--;
          y--;
          assert (text1.charAt(x) == text2.charAt(y))
                 : "No diagonal.  Can't happen. (diff_path1)";
          if (last_op == Operation.EQUAL) {
            path.getFirst().text = text1.charAt(x) + path.getFirst().text;
          } else {
            path.addFirst(new Diff(Operation.EQUAL, text1.substring(x, x + 1)));
          }
          last_op = Operation.EQUAL;
        }
      }
    }
    return path;
  }


  /**
   * Work from the middle back to the end to determine the path.
   * @param v_map List of path sets.
   * @param text1 Old string fragment to be diffed
   * @param text2 New string fragment to be diffed
   * @return LinkedList of Diff objects
   */
  protected LinkedList<Diff> diff_path2(List<Set<String>> v_map,
                                        String text1, String text2) {
    LinkedList<Diff> path = new LinkedList<Diff>();
    int x = text1.length();
    int y = text2.length();
    Operation last_op = null;
    for (int d = v_map.size() - 2; d >= 0; d--) {
      while (true) {
        if (v_map.get(d).contains((x - 1) + "," + y)) {
          x--;
          if (last_op == Operation.DELETE) {
            path.getLast().text += text1.charAt(text1.length() - x - 1);
          } else {
            path.addLast(new Diff(Operation.DELETE,
                text1.substring(text1.length() - x - 1, text1.length() - x)));
          }
          last_op = Operation.DELETE;
          break;
        } else if (v_map.get(d).contains(x + "," + (y - 1))) {
          y--;
          if (last_op == Operation.INSERT) {
            path.getLast().text += text2.charAt(text2.length() - y - 1);
          } else {
            path.addLast(new Diff(Operation.INSERT,
                text2.substring(text2.length() - y - 1, text2.length() - y)));
          }
          last_op = Operation.INSERT;
          break;
        } else {
          x--;
          y--;
          assert (text1.charAt(text1.length() - x - 1)
                  == text2.charAt(text2.length() - y - 1))
                 : "No diagonal.  Can't happen. (diff_path2)";
          if (last_op == Operation.EQUAL) {
            path.getLast().text += text1.charAt(text1.length() - x - 1);
          } else {
            path.addLast(new Diff(Operation.EQUAL,
                text1.substring(text1.length() - x - 1, text1.length() - x)));
          }
          last_op = Operation.EQUAL;
        }
      }
    }
    return path;
  }


  /**
   * Trim off common prefix
   * @param text1 First string
   * @param text2 Second string
   * @return The number of characters common to the start of each string.
   */
  public int diff_commonPrefix(String text1, String text2) {
    // Quick check for common null cases.
    if (text1.length() == 0 || text2.length() == 0 ||
        text1.charAt(0) != text2.charAt(0)) {
      return 0;
    }
    // Binary search.
    int pointermin = 0;
    int pointermax = Math.min(text1.length(), text2.length());
    int pointermid = pointermax;
    int pointerstart = 0;
    while (pointermin < pointermid) {
      if (text1.regionMatches(pointerstart, text2, pointerstart,
          pointermid - pointerstart)) {
        pointermin = pointermid;
        pointerstart = pointermin;
      } else {
        pointermax = pointermid;
      }
      pointermid = (pointermax - pointermin) / 2 + pointermin;
    }
    return pointermid;
  }

  
  /**
   * Trim off common suffix
   * @param text1 First string
   * @param text2 Second string
   * @return The number of characters common to the end of each string.
   */
  public int diff_commonSuffix(String text1, String text2) {
    // Quick check for common null cases.
    if (text1.length() == 0 || text2.length() == 0 ||
        text1.charAt(text1.length() - 1) != text2.charAt(text2.length() - 1)) {
      return 0;
    }
    // Binary search.
    int pointermin = 0;
    int pointermax = Math.min(text1.length(), text2.length());
    int pointermid = pointermax;
    int pointerend = 0;
    while (pointermin < pointermid) {
      if (text1.regionMatches(text1.length() - pointermid, text2,
                              text2.length() - pointermid,
                              pointermid - pointerend)) {
        pointermin = pointermid;
        pointerend = pointermin;
      } else {
        pointermax = pointermid;
      }
      pointermid = (pointermax - pointermin) / 2 + pointermin;
    }
    return pointermid;
  }


  /**
   * Do the two texts share a substring which is at least half the length of
   * the longer text?
   * @param text1 First string
   * @param text2 Second string
   * @return Five element String array, containing the prefix of text1, the
   *     suffix of text1, the prefix of text2, the suffix of text2 and the
   *     common middle.  Or null if there was no match.
   */
  protected String[] diff_halfMatch(String text1, String text2) {
    String longtext = text1.length() > text2.length() ? text1 : text2;
    String shorttext = text1.length() > text2.length() ? text2 : text1;
    if (longtext.length() < 10 || shorttext.length() < 1) {
      return null;  // Pointless.
    }

    // First check if the second quarter is the seed for a half-match.
    String[] hm1 = diff_halfMatchI(longtext, shorttext,
                                    (int) Math.ceil(longtext.length() / 4));
    // Check again based on the third quarter.
    String[] hm2 = diff_halfMatchI(longtext, shorttext,
                                    (int) Math.ceil(longtext.length() / 2));
    String[] hm;
    if (hm1 == null && hm2 == null) {
      return null;
    } else if (hm2 == null) {
      hm = hm1;
    } else if (hm1 == null) {
      hm = hm2;
    } else {
      // Both matched.  Select the longest.
      hm = hm1[4].length() > hm2[4].length() ? hm1 : hm2;
    }

    // A half-match was found, sort out the return data.
    if (text1.length() > text2.length()) {
      return hm;
      //return new String[]{hm[0], hm[1], hm[2], hm[3], hm[4]};
    } else {
      return new String[]{hm[2], hm[3], hm[0], hm[1], hm[4]};
    }
  }


  /**
   * Does a substring of shorttext exist within longtext such that the
   * substring is at least half the length of longtext?
   * @param longtext Longer string
   * @param shorttext Shorter string
   * @param i Start index of quarter length substring within longtext
   * @return Five element String array, containing the prefix of longtext, the
   *     suffix of longtext, the prefix of shorttext, the suffix of shorttext
   *     and the common middle.  Or null if there was no match.
   */
  private String[] diff_halfMatchI(String longtext, String shorttext, int i) {
    // Start with a 1/4 length substring at position i as a seed.
    String seed = longtext.substring(i,
        i + (int) Math.floor(longtext.length() / 4));
    int j = -1;
    String best_common = "";
    String best_longtext_a = "", best_longtext_b = "";
    String best_shorttext_a = "", best_shorttext_b = "";
    while ((j = shorttext.indexOf(seed, j + 1)) != -1) {
      int prefixLength = diff_commonPrefix(longtext.substring(i),
                                     shorttext.substring(j));
      int suffixLength = diff_commonSuffix(longtext.substring(0, i),
                                 shorttext.substring(0, j));
      if (best_common.length() < suffixLength + prefixLength) {
        best_common = shorttext.substring(j - suffixLength, j)
            + shorttext.substring(j, j + prefixLength);
        best_longtext_a = longtext.substring(0, i - suffixLength);
        best_longtext_b = longtext.substring(i + prefixLength);
        best_shorttext_a = shorttext.substring(0, j - suffixLength);
        best_shorttext_b = shorttext.substring(j + prefixLength);
      }
    }
    if (best_common.length() >= longtext.length() / 2) {
      return new String[]{best_longtext_a, best_longtext_b,
                          best_shorttext_a, best_shorttext_b, best_common};
    } else {
      return null;
    }
  }

  
  /**
   * Reduce the number of edits by eliminating semantically trivial equalities.
   * @param diffs LinkedList of Diff objects
   */
  public void diff_cleanupSemantic(LinkedList<Diff> diffs) {
    if (diffs.isEmpty()) {
      return;
    }
    boolean changes = false;
    Stack<Diff> equalities = new Stack<Diff>();  // Stack of qualities.
    String lastequality = null; // Always equal to equalities.lastElement().text
    ListIterator<Diff> pointer = diffs.listIterator();
    // Number of characters that changed prior to the equality.
    int length_changes1 = 0;
    // Number of characters that changed after the equality.
    int length_changes2 = 0;
    Diff thisDiff = pointer.next();
    while (thisDiff != null) {
      if (thisDiff.operation == Operation.EQUAL) {
        // equality found
        equalities.push(thisDiff);
        length_changes1 = length_changes2;
        length_changes2 = 0;
        lastequality = thisDiff.text;
      } else {
        // an insertion or deletion
        length_changes2 += thisDiff.text.length();
        if (lastequality != null && (lastequality.length() <= length_changes1)
            && (lastequality.length() <= length_changes2)) {
          //System.out.println("Splitting: '" + lastequality + "'");
          // Walk back to offending equality.
          while (thisDiff != equalities.lastElement()) {
            thisDiff = pointer.previous();
          }
          pointer.next();

          // Replace equality with a delete.
          pointer.set(new Diff(Operation.DELETE, lastequality));
          // Insert a coresponding an insert.
          pointer.add(new Diff(Operation.INSERT, lastequality));

          equalities.pop();  // Throw away the equality we just deleted.
          if (!equalities.empty()) {
            // Throw away the previous equality (it needs to be reevaluated).
            equalities.pop();
          }
          if (equalities.empty()) {
            // There are no previous equalities, walk back to the start.
            while (pointer.hasPrevious()) {
              pointer.previous();
            }
          } else {
            // There is a safe equality we can fall back to.
            thisDiff = equalities.lastElement();
            while (thisDiff != pointer.previous()) {
              // Intentionally empty loop.
            }
          }

          length_changes1 = 0;  // Reset the counters.
          length_changes2 = 0;
          lastequality = null;
          changes = true;
        }
      }
      thisDiff = pointer.hasNext() ? pointer.next() : null;
    }

    if (changes) {
      diff_cleanupMerge(diffs);
    }
    diff_cleanupSemanticLossless(diffs);
  }


  /**
   * Look for single edits surrounded on both sides by equalities
   * which can be shifted sideways to align the edit to a word boundary.
   * e.g: The c<ins>at c</ins>ame. -> The <ins>cat </ins>came.
   * @param diffs LinkedList of Diff objects
   */
  public void diff_cleanupSemanticLossless(LinkedList<Diff> diffs) {
    String equality1, edit, equality2;
    String commonString;
    int commonOffset;
    int score, bestScore;
    String bestEquality1, bestEdit, bestEquality2;
    // Create a new iterator at the start.
    ListIterator<Diff> pointer = diffs.listIterator();
    Diff prevDiff = pointer.hasNext() ? pointer.next() : null;
    Diff thisDiff = pointer.hasNext() ? pointer.next() : null;
    Diff nextDiff = pointer.hasNext() ? pointer.next() : null;
    // Intentionally ignore the first and last element (don't need checking).
    while (nextDiff != null) {
      if (prevDiff.operation == Operation.EQUAL &&
          nextDiff.operation == Operation.EQUAL) {
        // This is a single edit surrounded by equalities.
        equality1 = prevDiff.text;
        edit = thisDiff.text;
        equality2 = nextDiff.text;

        // First, shift the edit as far left as possible.
        commonOffset = diff_commonSuffix(equality1, edit);
        if (commonOffset != 0) {
          commonString = edit.substring(edit.length() - commonOffset);
          equality1 = equality1.substring(0, equality1.length() - commonOffset);
          edit = commonString + edit.substring(0, edit.length() - commonOffset);
          equality2 = commonString + equality2;
        }

        // Second, step character by character right, looking for the best fit.
        bestEquality1 = equality1;
        bestEdit = edit;
        bestEquality2 = equality2;
        bestScore = diff_cleanupSemanticScore(equality1, edit, equality2);
        while (edit.charAt(0) == equality2.charAt(0)) {
          equality1 += edit.charAt(0);
          edit = edit.substring(1) + equality2.charAt(0);
          equality2 = equality2.substring(1);
          score = diff_cleanupSemanticScore(equality1, edit, equality2);
          if (score >= bestScore) {
            bestScore = score;
            bestEquality1 = equality1;
            bestEdit = edit;
            bestEquality2 = equality2;
          }
        }

        if (!prevDiff.text.equals(bestEquality1)) {
          // We have an improvement, save it back to the diff.
          prevDiff.text = bestEquality1;
          thisDiff.text = bestEdit;
          nextDiff.text = bestEquality2;
        }
      }
      prevDiff = thisDiff;
      thisDiff = nextDiff;
      nextDiff = pointer.hasNext() ? pointer.next() : null;
    }
  }


  /**
   * Given three strings, compute a score representing whether the two internal
   * boundaries fall on word boundaries.
   * @param one First string
   * @param two Second string
   * @param three Third string
   * @return The score.
   */
  private int diff_cleanupSemanticScore(String one, String two, String three) {
    int score = 0;
    if (Character.isWhitespace(one.charAt(one.length() - 1))
        || Character.isWhitespace(two.charAt(0))) {
      score++;
    }
    if (Character.isWhitespace(two.charAt(two.length() - 1))
        || Character.isWhitespace(three.charAt(0))) {
      score++;
    }
    return score;
  }


  /**
   * Reduce the number of edits by eliminating operationally trivial equalities.
   * @param diffs LinkedList of Diff objects
   */
  public void diff_cleanupEfficiency(LinkedList<Diff> diffs) {
    if (diffs.isEmpty()) {
      return;
    }
    boolean changes = false;
    Stack<Diff> equalities = new Stack<Diff>();  // Stack of equalities.
    String lastequality = null; // Always equal to equalities.lastElement().text
    ListIterator<Diff> pointer = diffs.listIterator();
    // Is there an insertion operation before the last equality.
    boolean pre_ins = false;
    // Is there a deletion operation before the last equality.
    boolean pre_del = false;
    // Is there an insertion operation after the last equality.
    boolean post_ins = false;
    // Is there a deletion operation after the last equality.
    boolean post_del = false;
    Diff thisDiff = pointer.next();
    Diff safeDiff = thisDiff;  // The last Diff that is known to be unsplitable.
    while (thisDiff != null) {
      if (thisDiff.operation == Operation.EQUAL) {
        // equality found
        if (thisDiff.text.length() < Diff_EditCost && (post_ins || post_del)) {
          // Candidate found.
          equalities.push(thisDiff);
          pre_ins = post_ins;
          pre_del = post_del;
          lastequality = thisDiff.text;
        } else {
          // Not a candidate, and can never become one.
          equalities.clear();
          lastequality = null;
          safeDiff = thisDiff;
        }
        post_ins = post_del = false;
      } else {
        // an insertion or deletion
        if (thisDiff.operation == Operation.DELETE) {
          post_del = true;
        } else {
          post_ins = true;
        }
        /*
         * Five types to be split:
         * <ins>A</ins><del>B</del>XY<ins>C</ins><del>D</del>
         * <ins>A</ins>X<ins>C</ins><del>D</del>
         * <ins>A</ins><del>B</del>X<ins>C</ins>
         * <ins>A</del>X<ins>C</ins><del>D</del>
         * <ins>A</ins><del>B</del>X<del>C</del>
         */
        if (lastequality != null
            && ((pre_ins && pre_del && post_ins && post_del)
                || ((lastequality.length() < Diff_EditCost / 2)
                    && ((pre_ins ? 1 : 0) + (pre_del ? 1 : 0)
                        + (post_ins ? 1 : 0) + (post_del ? 1 : 0)) == 3))) {
          //System.out.println("Splitting: '" + lastequality + "'");
          // Walk back to offending equality.
          while (thisDiff != equalities.lastElement()) {
            thisDiff = pointer.previous();
          }
          pointer.next();

          // Replace equality with a delete.
          pointer.set(new Diff(Operation.DELETE, lastequality));
          // Insert a coresponding an insert.
          pointer.add(thisDiff = new Diff(Operation.INSERT, lastequality));

          equalities.pop();  // Throw away the equality we just deleted.
          lastequality = null;
          if (pre_ins && pre_del) {
            // No changes made which could affect previous entry, keep going.
            post_ins = post_del = true;
            equalities.clear();
            safeDiff = thisDiff;
          } else {
            if (!equalities.empty()) {
              // Throw away the previous equality (it needs to be reevaluated).
              equalities.pop();
            }
            if (equalities.empty()) {
              // There are no previous questionable equalities,
              // walk back to the last known safe diff.
              thisDiff = safeDiff;
            } else {
              // There is an equality we can fall back to.
              thisDiff = equalities.lastElement();
            }
            while (thisDiff != pointer.previous()) {
              // Intentionally empty loop.
            }
            post_ins = post_del = false;
          }

          changes = true;
        }
      }
      thisDiff = pointer.hasNext() ? pointer.next() : null;
    }

    if (changes) {
      diff_cleanupMerge(diffs);
    }
  }


  /**
   * Reorder and merge like edit sections.  Merge equalities.
   * Any edit section can move as long as it doesn't cross an equality.
   * @param diffs LinkedList of Diff objects
   */
  public void diff_cleanupMerge(LinkedList<Diff> diffs) {
    diffs.add(new Diff(Operation.EQUAL, ""));  // Add a dummy entry at the end.
    ListIterator<Diff> pointer = diffs.listIterator();
    int count_delete = 0;
    int count_insert = 0;
    String text_delete = "";
    String text_insert = "";
    Diff thisDiff = pointer.next();
    Diff prevEqual = null;
    int commonlength;
    while (thisDiff != null) {
      // System.out.println(diff);
      if (thisDiff.operation == Operation.INSERT) {
        count_insert++;
        text_insert += thisDiff.text;
        prevEqual = null;
      } else if (thisDiff.operation == Operation.DELETE) {
        count_delete++;
        text_delete += thisDiff.text;
        prevEqual = null;
      } else if (thisDiff.operation == Operation.EQUAL) {
        if (count_delete != 0 || count_insert != 0) {
          // Delete the offending records.
          pointer.previous();  // Reverse direction.
          while (count_delete-- > 0) {
            pointer.previous();
            pointer.remove();
          }
          while (count_insert-- > 0) {
            pointer.previous();
            pointer.remove();
          }
          if (count_delete != 0 && count_insert != 0) {
            // Factor out any common prefixies.
            commonlength = diff_commonPrefix(text_insert, text_delete);
            if (commonlength != 0) {
              if (pointer.hasPrevious()) {
                thisDiff = pointer.previous();
                assert thisDiff.operation == Operation.EQUAL
                       : "Previous diff should have been an equality.";
                thisDiff.text += text_insert.substring(0, commonlength);
                pointer.next();
              } else {
                pointer.add(new Diff(Operation.EQUAL,
                    text_insert.substring(0, commonlength)));
              }
              text_insert = text_insert.substring(commonlength);
              text_delete = text_delete.substring(commonlength);
            }
            // Factor out any common suffixies.
            commonlength = diff_commonSuffix(text_insert, text_delete);
            if (commonlength != 0) {
              thisDiff = pointer.next();
              thisDiff.text = text_insert.substring(text_insert.length()
                  - commonlength) + thisDiff.text;
              text_insert = text_insert.substring(0, text_insert.length()
                  - commonlength);
              text_delete = text_delete.substring(0, text_delete.length()
                  - commonlength);
              pointer.previous();
            }
          }
          // Insert the merged records.
          if (text_delete.length() != 0) {
            pointer.add(new Diff(Operation.DELETE, text_delete));
          }
          if (text_insert.length() != 0) {
            pointer.add(new Diff(Operation.INSERT, text_insert));
          }
          // Step forward to the equality.
          thisDiff = pointer.hasNext() ? pointer.next() : null;
        } else if (prevEqual != null) {
          // Merge this equality with the previous one.
          prevEqual.text += thisDiff.text;
          pointer.remove();
          thisDiff = pointer.previous();
          pointer.next();  // Forward direction
        }
        count_insert = 0;
        count_delete = 0;
        text_delete = "";
        text_insert = "";
        prevEqual = thisDiff;
      } else {
        assert false : thisDiff.operation;  // Can't happen.
      }
      thisDiff = pointer.hasNext() ? pointer.next() : null;
    }
    // System.out.println(diff);
    if (diffs.getLast().text.length() == 0) {
      diffs.removeLast();  // Remove the dummy entry at the end.
    }

    /*
     * Second pass: look for single edits surrounded on both sides by equalities
     * which can be shifted sideways to eliminate an equality.
     * e.g: A<ins>BA</ins>C -> <ins>AB</ins>AC
     */
    boolean changes = false;
    // Create a new iterator at the start.
    // (As opposed to walking the current one back.)
    pointer = diffs.listIterator();
    Diff prevDiff = pointer.hasNext() ? pointer.next() : null;
    thisDiff = pointer.hasNext() ? pointer.next() : null;
    Diff nextDiff = pointer.hasNext() ? pointer.next() : null;
    // Intentionally ignore the first and last element (don't need checking).
    while (nextDiff != null) {
      if (prevDiff.operation == Operation.EQUAL &&
          nextDiff.operation == Operation.EQUAL) {
        // This is a single edit surrounded by equalities.
        if (thisDiff.text.endsWith(prevDiff.text)) {
          // Shift the edit over the previous equality.
          thisDiff.text = prevDiff.text +
              thisDiff.text.substring(0, thisDiff.text.length() -
                                          prevDiff.text.length());
          nextDiff.text = prevDiff.text + nextDiff.text;
          pointer.previous(); // Walk past nextDiff.
          pointer.previous(); // Walk past thisDiff.
          pointer.previous(); // Walk past prevDiff.
          pointer.remove(); // Delete prevDiff.
          pointer.next(); // Walk past thisDiff.
          thisDiff = pointer.next(); // Walk past nextDiff.
          nextDiff = pointer.hasNext() ? pointer.next() : null;
          changes = true;
        } else if (thisDiff.text.startsWith(nextDiff.text)) {
          // Shift the edit over the next equality.
          prevDiff.text += nextDiff.text;
          thisDiff.text = thisDiff.text.substring(nextDiff.text.length()) +
              nextDiff.text;
          pointer.remove(); // Delete nextDiff.
          nextDiff = pointer.hasNext() ? pointer.next() : null;
          changes = true;
        }
      }
      prevDiff = thisDiff;
      thisDiff = nextDiff;
      nextDiff = pointer.hasNext() ? pointer.next() : null;
    }
    // If shifts were made, the diff needs reordering and another shift sweep.
    if (changes) {
      diff_cleanupMerge(diffs);
    }
  }


  /**
   * Add an index to each Diff, represents where the Diff is located in text2.
   * e.g. [(DELETE, "h", 0), (INSERT, "c", 0), (EQUAL, "at", 1)]
   * @param diffs LinkedList of Diff objects
   */
  public void diff_addIndex(LinkedList<Diff> diffs) {
    int i = 0;
    for (Diff aDiff : diffs) {
      aDiff.index = i;
      if (aDiff.operation != Operation.DELETE) {
        i += aDiff.text.length();
      }
    }
  }


  /**
   * loc is a location in text1, compute and return the equivalent location in
   * text2.
   * e.g. "The cat" vs "The big cat", 1->1, 5->8
   * @param diffs LinkedList of Diff objects
   * @param loc Location within text1
   * @return Location within text2
   */
  public int diff_xIndex(LinkedList<Diff> diffs, int loc) {
    int chars1 = 0;
    int chars2 = 0;
    int last_chars1 = 0;
    int last_chars2 = 0;
    Diff lastDiff = null;
    for (Diff aDiff : diffs) {
      if (aDiff.operation != Operation.INSERT) {
        // Equality or deletion.
        chars1 += aDiff.text.length();
      }
      if (aDiff.operation != Operation.DELETE) {
        // Equality or insertion.
        chars2 += aDiff.text.length();
      }
      if (chars1 > loc) {
        // Overshot the location.
        lastDiff = aDiff;
        break;
      }
      last_chars1 = chars1;
      last_chars2 = chars2;
    }
    if (lastDiff != null && lastDiff.operation == Operation.DELETE) {
      // The location was deleted.
      return last_chars2;
    }
    // Add the remaining character length.
    return last_chars2 + (loc - last_chars1);
  }


  /**
   * Convert a Diff list into a pretty HTML report.
   * @param diffs LinkedList of Diff objects
   * @return HTML representation
   */
  public String diff_prettyHtml(LinkedList<Diff> diffs) {
    diff_addIndex(diffs);
    StringBuilder html = new StringBuilder();
    String text;
    for (Diff aDiff : diffs) {
      text = aDiff.text;
      text = text.replaceAll("&", "&amp;").replaceAll("<", "&lt;")
                 .replaceAll(">", "&gt;").replaceAll("\n", "&para;<BR>");
      if (aDiff.operation == Operation.DELETE) {
        html.append("<DEL STYLE=\"background:#FFE6E6;\" TITLE=\"i=" + aDiff.index
                + "\">" + text + "</DEL>");
      } else if (aDiff.operation == Operation.INSERT) {
        html.append("<INS STYLE=\"background:#E6FFE6;\" TITLE=\"i=" + aDiff.index
                + "\">" + text + "</INS>");
      } else {
        html.append("<SPAN TITLE=\"i=" + aDiff.index + "\">" + text + "</SPAN>");
      }
    }
    return html.toString();
  }

  /**
   * Compute and return the source text (all equalities and deletions).
   * @param diffs LinkedList of Diff objects
   * @return Source text
   */
  public String diff_text1(LinkedList<Diff> diffs) {
    StringBuilder txt = new StringBuilder();
    for (Diff aDiff : diffs) {
      if (aDiff.operation != Operation.INSERT) {
        txt.append(aDiff.text);
      }
    }
    return txt.toString();
  }

  /**
   * Compute and return the destination text (all equalities and insertions).
   * @param diffs LinkedList of Diff objects
   * @return Destination text
   */
  public String diff_text2(LinkedList<Diff> diffs) {
    StringBuilder txt = new StringBuilder();
    for (Diff aDiff : diffs) {
      if (aDiff.operation != Operation.DELETE) {
        txt.append(aDiff.text);
      }
    }
    return txt.toString();
  }

  
  /**
   * Crush the diff into an encoded string which describes the operations
   * required to transform text1 into text2.
   * E.g. =3\t-2\t+ing\t  -> Keep 3 chars, delete 2 chars, insert 'ing'.
   * Operations are tab-separated.  Inserted text is escaped using %xx notation.
   * @param {Array} diffs Array of diff tuples
   * @return {String} Delta text
   */
  public String diff_toDelta(LinkedList<Diff> diffs) {
    StringBuilder txt = new StringBuilder();
    for (Diff aDiff : diffs) {
      switch(aDiff.operation) {
        case DELETE:
          txt.append("-" + aDiff.text.length() + "\t");
          break;
        case EQUAL:
          txt.append("=" + aDiff.text.length() + "\t");
          break;
        case INSERT:
          try {
            txt.append("+" + URLEncoder.encode(aDiff.text, "UTF-8")
                                       .replace('+', ' ') + "\t");
          } catch (UnsupportedEncodingException e) {
            // This is a system which does not support UTF-8.  (Not likely)
            System.out.println("Error in diff_toDelta: " + e);
            return "";
          }
          break;
        default:
          assert false : "Invalid diff operation in diff_toDelta()";
      }
    }
    return txt.toString().replace("%20", " ");
  }


  /**
   * Given the original text1, and an encoded string which describes the
   * operations required to transform text1 into text2, compute the full diff.
   * @param {String} text1 Source string for the diff
   * @param {String} delta Delta text
   * @return {Array} Array of diff tuples
   */
  public LinkedList<Diff> diff_fromDelta(String text1, String delta) {
    LinkedList<Diff> diffs = new LinkedList<Diff>();
    int pointer = 0;  // Cursor in text1
    String[] tokens = delta.split("\t");
    for (String token : tokens) {
      if (token.length() == 0) {
        // Blank tokens are ok (from a trailing \t).
        continue;
      }
      String param = token.substring(1);
      switch(token.charAt(0)) {
        case '-':
          // Fall through.
        case '=':
          int n;
          try {
            n = Integer.parseInt(param);
          } catch (NumberFormatException e) {
            System.out.println("Error in diff_fromDelta: " + e);
            n = 0;
          }
          assert n >= 0 : "Invalid number in diff_fromDelta()";
          String text = text1.substring(pointer, pointer += n);
          if (token.charAt(0) == '=') {
            diffs.add(new Diff(Operation.EQUAL, text));
          } else {
            diffs.add(new Diff(Operation.DELETE, text));
          }
          break;
        case '+':
          try {
            param = URLDecoder.decode(param, "UTF-8");
          } catch (UnsupportedEncodingException e) {
            // This is a system which does not support UTF-8.  (Not likely)
            System.out.println("Error in diff_fromDelta: " + e);
            param = "";
          }
          diffs.add(new Diff(Operation.INSERT, param));
          break;
        default:
          // Anything else is an error.
          assert false : "Invalid diff operation in diff_fromDelta()";
      }
    }
    assert pointer == text1.length() : "Text length mismatch in diff_fromDelta()";
    return diffs;
  }


  //  MATCH FUNCTIONS


  /**
   * Locate the best instance of 'pattern' in 'text' near 'loc'.
   * Returns -1 if no match found.
   * @param text The text to search
   * @param pattern The pattern to search for
   * @param loc The location to search around
   * @return Best match index or -1
   */
  public int match_main(String text, String pattern, int loc) {
    loc = Math.max(0, Math.min(loc, text.length() - pattern.length()));
    if (text.equals(pattern)) {
      // Shortcut (potentially not guaranteed by the algorithm)
      return 0;
    } else if (text.length() == 0) {
      // Nothing to match.
      return -1;
    } else if (text.substring(loc, loc + pattern.length()).equals(pattern)) {
      // Perfect match at the perfect spot!  (Includes case of null pattern)
      return loc;
    } else {
      // Do a fuzzy compare.
      return match_bitap(text, pattern, loc);
    }
  }


  /**
   * Locate the best instance of 'pattern' in 'text' near 'loc' using the
   * Bitap algorithm.  Returns -1 if no match found.
   * @param text The text to search
   * @param pattern The pattern to search for
   * @param loc The location to search around
   * @return Best match index or -1
   */
  public int match_bitap(String text, String pattern, int loc) {
    assert (Match_MaxBits == 0 || pattern.length() <= Match_MaxBits)
        : "Pattern too long for this application.";

    // Initialise the alphabet.
    Map<Character, Integer> s = match_alphabet(pattern);

    int score_text_length = text.length();
    // Coerce the text length between reasonable maximums and minimums.
    score_text_length = Math.max(score_text_length, Match_MinLength);
    score_text_length = Math.min(score_text_length, Match_MaxLength);

    // Highest score beyond which we give up.
    double score_threshold = Match_Threshold;
    // Is there a nearby exact match? (speedup)
    int best_loc = text.indexOf(pattern, loc);
    if (best_loc != -1) {
      score_threshold = Math.min(match_bitapScore(0, best_loc, loc,
          score_text_length, pattern), score_threshold);
    }
    // What about in the other direction? (speedup)
    best_loc = text.lastIndexOf(pattern, loc + pattern.length());
    if (best_loc != -1) {
      score_threshold = Math.min(match_bitapScore(0, best_loc, loc,
          score_text_length, pattern), score_threshold);
    }

    // Initialise the bit arrays.
    int matchmask = 1 << (pattern.length() - 1);
    best_loc = -1;

    int bin_min, bin_mid;
    int bin_max = Math.max(loc + loc, text.length());
    // Empty initialization added to appease Java compiler.
    int[] last_rd = new int[0];
    for (int d = 0; d < pattern.length(); d++) {
      // Scan for the best match; each iteration allows for one more error.
      int[] rd = new int[text.length()];

      // Run a binary search to determine how far from 'loc' we can stray at
      // this error level.
      bin_min = loc;
      bin_mid = bin_max;
      while (bin_min < bin_mid) {
        if (match_bitapScore(d, bin_mid, loc, score_text_length, pattern)
            < score_threshold) {
          bin_min = bin_mid;
        } else {
          bin_max = bin_mid;
        }
        bin_mid = (bin_max - bin_min) / 2 + bin_min;
      }
      // Use the result from this iteration as the maximum for the next.
      bin_max = bin_mid;
      int start = Math.max(0, loc - (bin_mid - loc) - 1);
      int finish = Math.min(text.length() - 1, pattern.length() + bin_mid);

      if (text.charAt(finish) == pattern.charAt(pattern.length() - 1)) {
        rd[finish] = (1 << (d + 1)) - 1;
      } else {
        rd[finish] = (1 << d) - 1;
      }
      for (int j = finish - 1; j >= start; j--) {
        if (d == 0) {
          // First pass: exact match.
          rd[j] = ((rd[j + 1] << 1) | 1) & (s.containsKey(text.charAt(j))
              ? s.get(text.charAt(j))
              : 0);
        } else {
          // Subsequent passes: fuzzy match.
          rd[j] = ((rd[j + 1] << 1) | 1) & (s.containsKey(text.charAt(j))
              ? s.get(text.charAt(j)) : 0) | ((last_rd[j + 1] << 1) | 1)
              | ((last_rd[j] << 1) | 1) | last_rd[j + 1];
        }
        if ((rd[j] & matchmask) != 0) {
          double score = match_bitapScore(d, j, loc, score_text_length,
                                           pattern);
          // This match will almost certainly be better than any existing
          // match.  But check anyway.
          if (score <= score_threshold) {
            // Told you so.
            score_threshold = score;
            best_loc = j;
            if (j > loc) {
              // When passing loc, don't exceed our current distance from loc.
              start = Math.max(0, loc - (j - loc));
            } else {
              // Already passed loc, downhill from here on in.
              break;
            }
          }
        }
      }
      if (match_bitapScore(d + 1, loc, loc, score_text_length, pattern)
          > score_threshold) {
        // No hope for a (better) match at greater error levels.
        break;
      }
      last_rd = rd;
    }
    return best_loc;
  }


  /**
   * Compute and return the score for a match with e errors and x location.
   * @param e Number of errors in match
   * @param x Location of match
   * @param loc Expected location of match
   * @param score_text_length Coerced version of text's length
   * @param pattern Pattern being sought
   * @return Overall score for match
   */
  private double match_bitapScore(int e, int x, int loc,
                                  int score_text_length, String pattern) {
    int d = Math.abs(loc - x);
    return (e / (float) pattern.length() / Match_Balance)
        + (d / (float) score_text_length / (1.0 - Match_Balance));
  }


  /**
   * Initialise the alphabet for the Bitap algorithm.
   * @param pattern The text to encode
   * @return Hash of character locations
   */
  protected Map<Character, Integer> match_alphabet(String pattern) {
    Map<Character, Integer> s = new HashMap<Character, Integer>();
    char[] char_pattern = pattern.toCharArray();
    for (char c : char_pattern) {
      s.put(c, 0);
    }
    int i = 0;
    for (char c : char_pattern) {
      s.put(c, s.get(c) | (1 << (pattern.length() - i - 1)));
      i++;
    }
    return s;
  }


  //  PATCH FUNCTIONS


  /**
   * Increase the context until it is unique,
   * but don't let the pattern expand beyond Match_MaxBits.
   * @param patch The patch to grow
   * @param text Source text
   */
  public void patch_addContext(Patch patch, String text) {
    String pattern = text.substring(patch.start2, patch.start2 + patch.length1);
    int padding = 0;
    // Increase the context until we're unique (but don't let the pattern
    // expand beyond Match_MaxBits).
    while (text.indexOf(pattern) != text.lastIndexOf(pattern)
        && pattern.length() < Match_MaxBits - Patch_Margin - Patch_Margin) {
      padding += Patch_Margin;
      pattern = text.substring(Math.max(0, patch.start2 - padding),
          Math.min(text.length(), patch.start2 + patch.length1 + padding));
    }
    // Add one chunk for good luck.
    padding += Patch_Margin;
    // Add the prefix.
    String prefix = text.substring(Math.max(0, patch.start2 - padding),
        patch.start2);
    if (prefix.length() != 0) {
      patch.diffs.addFirst(new Diff(Operation.EQUAL, prefix));
    }
    // Add the suffix.
    String suffix = text.substring(patch.start2 + patch.length1,
        Math.min(text.length(), patch.start2 + patch.length1 + padding));
    if (suffix.length() != 0) {
      patch.diffs.addLast(new Diff(Operation.EQUAL, suffix));
    }

    // Roll back the start points.
    patch.start1 -= prefix.length();
    patch.start2 -= prefix.length();
    // Extend the lengths.
    patch.length1 += prefix.length() + suffix.length();
    patch.length2 += prefix.length() + suffix.length();
  }


  /**
   * Compute a list of patches to turn text1 into text2.
   * A set of diffs will be computed.
   * @param text1 Old text
   * @param text2 New text
   * @return LinkedList of Patch objects.
   */
  public LinkedList<Patch> patch_make(String text1, String text2) {
    // No diffs provided, compute our own.
    LinkedList<Diff> diffs = diff_main(text1, text2, true);
    if (diffs.size() > 2) {
      diff_cleanupSemantic(diffs);
      diff_cleanupEfficiency(diffs);
    }
    return patch_make(text1, text2, diffs);
  }


  /**
   * Compute a list of patches to turn text1 into text2.
   * Use the diffs provided.
   * @param text1 Old text
   * @param text2 New text
   * @param diffs Optional array of diff tuples for text1 to text2.
   * @return LinkedList of Patch objects.
   */
  public LinkedList<Patch> patch_make(String text1, String text2,
                                      LinkedList<Diff> diffs) {
    LinkedList<Patch> patches = new LinkedList<Patch>();
    if (diffs.isEmpty()) {
      return patches;  // Get rid of the null case.
    }
    Patch patch = new Patch();
    int char_count1 = 0;  // Number of characters into the text1 string.
    int char_count2 = 0;  // Number of characters into the text2 string.
    // Recreate the patches to determine context info.
    String prepatch_text = text1;
    String postpatch_text = text1;
    for (Diff aDiff : diffs) {
      if (patch.diffs.isEmpty() && aDiff.operation != Operation.EQUAL) {
        // A new patch starts here.
        patch.start1 = char_count1;
        patch.start2 = char_count2;
      }

      if (aDiff.operation == Operation.INSERT) {
        // Insertion
        patch.diffs.add(aDiff);
        patch.length2 += aDiff.text.length();
        postpatch_text = postpatch_text.substring(0, char_count2)
            + aDiff.text + postpatch_text.substring(char_count2);
      } else if (aDiff.operation == Operation.DELETE) {
        // Deletion.
        patch.length1 += aDiff.text.length();
        patch.diffs.add(aDiff);
        postpatch_text = postpatch_text.substring(0, char_count2)
            + postpatch_text.substring(char_count2 + aDiff.text.length());
      } else if (aDiff.operation == Operation.EQUAL
          && aDiff.text.length() <= 2 * Patch_Margin
          && !patch.diffs.isEmpty() && aDiff != diffs.getLast()) {
        // Small equality inside a patch.
        patch.diffs.add(aDiff);
        patch.length1 += aDiff.text.length();
        patch.length2 += aDiff.text.length();
      }

      if (aDiff.operation == Operation.EQUAL
          && aDiff.text.length() >= 2 * Patch_Margin) {
        // Time for a new patch.
        if (!patch.diffs.isEmpty()) {
          patch_addContext(patch, prepatch_text);
          patches.add(patch);
          patch = new Patch();
          prepatch_text = postpatch_text;
        }
      }

      // Update the current character count.
      if (aDiff.operation != Operation.INSERT) {
        char_count1 += aDiff.text.length();
      }
      if (aDiff.operation != Operation.DELETE) {
        char_count2 += aDiff.text.length();
      }
    }
    // Pick up the leftover patch if not empty.
    if (!patch.diffs.isEmpty()) {
      patch_addContext(patch, prepatch_text);
      patches.add(patch);
    }

    return patches;
  }


  /**
   * Merge a set of patches onto the text.  Return a patched text, as well
   * as an array of true/false values indicating which patches were applied.
   * @param patches Array of patch objects
   * @param text Old text
   * @return Two element Object array, containing the new text and an array of
   *      boolean values
   */
  public Object[] patch_apply(LinkedList<Patch> patches, String text) {
    patch_splitMax(patches);
    boolean[] results = new boolean[patches.size()];
    int delta = 0;
    int expected_loc, start_loc;
    String text1, text2;
    int index1, index2;
    LinkedList<Diff> diffs;
    int x = 0;
    for (Patch aPatch : patches) {
      expected_loc = aPatch.start2 + delta;
      text1 = diff_text1(aPatch.diffs);
      start_loc = match_main(text, text1, expected_loc);
      if (start_loc == -1) {
        // No match found.  :(
        results[x] = false;
      } else {
        // Found a match.  :)
        results[x] = true;
        delta = start_loc - expected_loc;
        text2 = text.substring(start_loc, start_loc + text1.length());
        if (text1.equals(text2)) {
          // Perfect match, just shove the replacement text in.
          text = text.substring(0, start_loc) + diff_text2(aPatch.diffs)
              + text.substring(start_loc + text1.length());
        } else {
          // Imperfect match.  Run a diff to get a framework of equivalent
          // indicies.
          diffs = diff_main(text1, text2, false);
          diff_cleanupSemanticLossless(diffs);
          index1 = 0;
          for (Diff aDiff : aPatch.diffs) {
            if (aDiff.operation != Operation.EQUAL) {
              index2 = diff_xIndex(diffs, index1);
              if (aDiff.operation == Operation.INSERT) {
                // Insertion
                text = text.substring(0, start_loc + index2) + aDiff.text
                    + text.substring(start_loc + index2);
              } else if (aDiff.operation == Operation.DELETE) {
                // Deletion
                text = text.substring(0, start_loc + index2)
                    + text.substring(start_loc + diff_xIndex(diffs,
                    index1 + aDiff.text.length()));
              }
            }
            if (aDiff.operation != Operation.DELETE) {
              index1 += aDiff.text.length();
            }
          }
        }
      }
      x++;
    }
    return new Object[]{text, results};
  }


  /**
   * Look through the patches and break up any which are longer than the
   * maximum limit of the match algorithm.
   * @param patches LinkedList of Patch objects.
   */
  public void patch_splitMax(LinkedList<Patch> patches) {
    int patch_size;
    String precontext, postcontext;
    Patch patch;
    int start1, start2;
    boolean empty;
    Operation diff_type;
    String diff_text;
    ListIterator<Patch> pointer = patches.listIterator();
    Patch bigpatch = pointer.hasNext() ? pointer.next() : null;
    while (bigpatch != null) {
      if (bigpatch.length1 <= Match_MaxBits) {
        bigpatch = pointer.hasNext() ? pointer.next() : null;
        continue;
      }
      // Remove the big old patch.
      pointer.remove();
      patch_size = Match_MaxBits;
      start1 = bigpatch.start1;
      start2 = bigpatch.start2;
      precontext = "";
      while (!bigpatch.diffs.isEmpty()) {
        // Create one of several smaller patches.
        patch = new Patch();
        empty = true;
        patch.start1 = start1 - precontext.length();
        patch.start2 = start2 - precontext.length();
        if (precontext.length() != 0) {
          patch.length1 = patch.length2 = precontext.length();
          patch.diffs.add(new Diff(Operation.EQUAL, precontext));
        }
        while (!bigpatch.diffs.isEmpty()
            && patch.length1 < patch_size - Patch_Margin) {
          diff_type = bigpatch.diffs.getFirst().operation;
          diff_text = bigpatch.diffs.getFirst().text;
          if (diff_type == Operation.INSERT) {
            // Insertions are harmless.
            patch.length2 += diff_text.length();
            start2 += diff_text.length();
            patch.diffs.addLast(bigpatch.diffs.removeFirst());
            empty = false;
          } else {
            // Deletion or equality.  Only take as much as we can stomach.
            diff_text = diff_text.substring(0, Math.min(diff_text.length(),
                patch_size - patch.length1 - Patch_Margin));
            patch.length1 += diff_text.length();
            start1 += diff_text.length();
            if (diff_type == Operation.EQUAL) {
              patch.length2 += diff_text.length();
              start2 += diff_text.length();
            } else {
              empty = false;
            }
            patch.diffs.add(new Diff(diff_type, diff_text));
            if (diff_text.equals(bigpatch.diffs.getFirst().text)) {
              bigpatch.diffs.removeFirst();
            } else {
              bigpatch.diffs.getFirst().text = bigpatch.diffs.getFirst().text
                  .substring(diff_text.length());
            }
          }
        }
        // Compute the head context for the next patch.
        precontext = diff_text2(patch.diffs);
        precontext = precontext.substring(precontext.length() - Patch_Margin);
        // Append the end context for this patch.
        if (diff_text1(bigpatch.diffs).length() > Patch_Margin) {
          postcontext = diff_text1(bigpatch.diffs).substring(0, Patch_Margin);
        } else {
          postcontext = diff_text1(bigpatch.diffs);
        }
        if (postcontext.length() != 0) {
          patch.length1 += postcontext.length();
          patch.length2 += postcontext.length();
          if (!patch.diffs.isEmpty()
              && patch.diffs.getLast().operation == Operation.EQUAL) {
            patch.diffs.getLast().text += postcontext;
          } else {
            patch.diffs.add(new Diff(Operation.EQUAL, postcontext));
          }
        }
        if (!empty) {
          pointer.add(patch);
        }
      }
      bigpatch = pointer.hasNext() ? pointer.next() : null;
    }
  }


  /**
   * Take a list of patches and return a textual representation.
   * @param patches List of Patch objects.
   * @return Text representation of patches.
   */
  public String patch_toText(List<Patch> patches) {
    StringBuilder text = new StringBuilder();
    for (Patch aPatch : patches) {
      text.append(aPatch);
    }
    return text.toString();
  }


  /**
   * Parse a textual representation of patches and return a List of Patch
   * objects.
   * @param textline Text representation of patches
   * @return List of Patch objects
   */
  public List<Patch> patch_fromText(String textline) {
    List<Patch> patches = new LinkedList<Patch>();
    List<String> textList = Arrays.asList(textline.split("\n"));
    LinkedList<String> text = new LinkedList<String>(textList);
    Patch patch;
    Pattern patchHeader
        = Pattern.compile("^@@ -(\\d+),?(\\d*) \\+(\\d+),?(\\d*) @@$");
    Matcher m;
    char sign;
    String line;
    while (!text.isEmpty()) {
      m = patchHeader.matcher(text.getFirst());
      m.matches();
      assert m.groupCount() == 4
          : "Invalid patch string:\n" + text.getFirst();
      patch = new Patch();
      patches.add(patch);
      patch.start1 = Integer.parseInt(m.group(1));
      if (m.group(2).length() == 0) {
        patch.start1--;
        patch.length1 = 1;
      } else if (m.group(2).equals("0")) {
        patch.length1 = 0;
      } else {
        patch.start1--;
        patch.length1 = Integer.parseInt(m.group(2));
      }

      patch.start2 = Integer.parseInt(m.group(3));
      if (m.group(4).length() == 0) {
        patch.start2--;
        patch.length2 = 1;
      } else if (m.group(4).equals("0")) {
        patch.length2 = 0;
      } else {
        patch.start2--;
        patch.length2 = Integer.parseInt(m.group(4));
      }
      text.removeFirst();

      while (!text.isEmpty()) {
        try {
          sign = text.getFirst().charAt(0);
        } catch (IndexOutOfBoundsException e) {
          // Blank line?  Whatever.
          text.removeFirst();
          continue;
        }
        line = text.getFirst().substring(1);
        line = line.replace("+", "%2B");  // decode would change all "+" to " "
        try {
          line = URLDecoder.decode(line, "UTF-8");
        } catch (UnsupportedEncodingException e) {
          // This is a system which does not support UTF-8.  (Not likely)
          System.out.println("Error in Patch.toString: " + e);
          line = "";
        }
        if (sign == '-') {
          // Deletion.
          patch.diffs.add(new Diff(Operation.DELETE, line));
        } else if (sign == '+') {
          // Insertion.
          patch.diffs.add(new Diff(Operation.INSERT, line));
        } else if (sign == ' ') {
          // Minor equality.
          patch.diffs.add(new Diff(Operation.EQUAL, line));
        } else if (sign == '@') {
          // Start of next patch.
          break;
        } else {
          // WTF?
          assert false : "Invalid patch mode: '" + sign + "'\n" + line;
        }
        text.removeFirst();
      }
    }
    return patches;
  }
}


/**
 * Class representing one diff operation.
 */
class Diff {
  public diff_match_patch.Operation operation;
  // One of: INSERT, DELETE or EQUAL.
  public String text;
  // The text associated with this diff operation.
  public int index;
  // Where in the source text does this diff fit?  Not usualy set.
  
  /**
   * Constructor.  Initializes the diff with the provided values.
   * @param operation One of INSERT, DELETE or EQUAL
   * @param text The text being applied
   */
  public Diff(diff_match_patch.Operation operation, String text) {
    // Construct a diff with the specified operation and text.
    this.operation = operation;
    this.text = text;
    this.index = -1;
  }

  /**
   * Display a human-readable version of this Diff.
   * @return text version
   */
  public String toString() {
    String prettyText = this.text.replace('\n', '\u00b6');
    return "Diff(" + this.operation + ",\"" + prettyText + "\")";
  }

  /**
   * Is this Diff equivalent to another Diff?
   * @param d Another Diff to compare against
   * @return true or false
   */
  public boolean equals(Object d) {
    try {
      return (((Diff) d).operation == this.operation)
             && (((Diff) d).text.equals(this.text));
    } catch (ClassCastException e) {
      return false;
    }
  }

  /**
   *
   * @return number represending this object's values
   */
  public int hashCode() {
    return this.operation.hashCode() + this.text.hashCode();
  }
}


/**
 * Class representing one patch operation.
 */
class Patch {
  public LinkedList<Diff> diffs;
  public int start1;
  public int start2;
  public int length1;
  public int length2;
  
  /**
   * Constructor.  Initializes with an empty list of diffs.
   */
  public Patch() {
    this.diffs = new LinkedList<Diff>();
  }

  /**
   * Emmulate GNU diff's format.
   * Header: @@ -382,8 +481,9 @@
   * Indicies are printed as 1-based, not 0-based.
   * @return The GNU diff string
   */
  public String toString() {
    String coords1, coords2;
    if (this.length1 == 0) {
      coords1 = this.start1 + ",0";
    } else if (this.length1 == 1) {
      coords1 = Integer.toString(this.start1 + 1);
    } else {
      coords1 = (this.start1 + 1) + "," + this.length1;
    }
    if (this.length2 == 0) {
      coords2 = this.start2 + ",0";
    } else if (this.length2 == 1) {
      coords2 = Integer.toString(this.start2 + 1);
    } else {
      coords2 = (this.start2 + 1) + "," + this.length2;
    }
    StringBuilder txt = new StringBuilder();
    txt.append("@@ -" + coords1 + " +" + coords2 + " @@\n");
    // Escape the body of the patch with %xx notation.
    for (Diff aDiff : this.diffs) {
      switch(aDiff.operation) {
      case DELETE:
        txt.append('-');
        break;
      case EQUAL:
        txt.append(' ');
        break;
      case INSERT:
        txt.append('+');
        break;
      default:
        assert false : "Invalid diff operation in patch_obj.toString()";
      }
      try {
        txt.append(URLEncoder.encode(aDiff.text, "UTF-8").replace('+', ' ') + "\n");
      } catch (UnsupportedEncodingException e) {
        // This is a system which does not support UTF-8.  (Not likely)
        System.out.println("Error in Patch.toString: " + e);
        return "";
      }
    }
    // Replicate the JavaScript encodeURI() function (not including %20)
    String txtString = txt.toString()
             .replace("%3D", "=").replace("%3B", ";").replace("%27", "'")
             .replace("%2C", ",").replace("%2F", "/").replace("%7E", "~")
             .replace("%21", "!").replace("%40", "@").replace("%23", "#")
             .replace("%24", "$").replace("%26", "&").replace("%28", "(")
             .replace("%29", ")").replace("%2B", "+").replace("%3A", ":")
             .replace("%3F", "?");
    return txtString;
  }
}