LINQToDiff.cs

  /// <summary>
  ///    This snippet extends Matthias Hertel's Difference algorithm and extends it to a 
  ///    LINQ provider proof-of-concept.  To run, simply copy+paste into LINQPad.
  ///  
  ///    http://www.mathertel.de/Diff/
  ///
  /// Copyright (c) by Matthias Hertel, http://www.mathertel.de
  /// This work is licensed under a BSD style license. See http://www.mathertel.de/License.aspx
  /// 
  /// </summary>


void Main()
{
	var d1 = "HELLO cruel world".Split(' ');
	var d2 = "Hello happy   world".Split(' ');
	
	var s = from item in DiffList(d1, d2)
			where item != ""
			select Regex.Replace(item.ToLower().Trim(), @"\s+", " ");
	
	s.Dump();
}

public DiffSource<T> DiffList<T>(IEnumerable<T> list1, IEnumerable<T> list2) {
	return new DiffSource<T>(list1, list2);
}

public class DiffSource<T> : IEnumerable<Change<T>> {
	IEnumerable<T> _input, _output;
  	public DiffSource(IEnumerable<T> input, IEnumerable<T> output) {
		_input = input; _output = output;
	}
	public DiffSource<TNew> Select<TNew>(Func<T, TNew> f) {
		return new DiffSource<TNew>(_input.Select(f), _output.Select(f));
	}
	public IEnumerator<Change<T>> GetEnumerator() {
		return FullDiff<T>(_input, _output).GetEnumerator();
	}
	IEnumerator IEnumerable.GetEnumerator() {
		return this.GetEnumerator();
	}

//	public IEnumerable<Change<T>> Diff() {
//	  return FullDiff<T>(_input, _output);
//	}
	public DiffSource<T> Where(Func<T, bool> pred) {
		return new DiffSource<T>(_input.Where(pred).AsEnumerable(), _output.Where(pred).AsEnumerable());
	}
}

void TestStringGeneric() {
   var h = new Hashtable();
   var d = new Diff();
   var list1 = "1,2,5,6,8".Dump().Split(',').ToArray();
   var list2 = "1,2,3,4,6,7,8,9".Dump().Split(',').ToArray();
   var results = Diff.DiffT(list1, list2).Dump();
   var q1 = Report(results, list1, list2).Dump();
}

struct Status<T> {
  public bool exists;
  public T value;
  public Status(T value, bool exists) {
    if(this.exists = exists) {
		this.value = value;
	} else {
		this.value = default(T);
	}
  }
}

public struct Change<T> {
	public int? left_index, right_index;
	public T left, right;
	public bool deleted, inserted, same;
	public bool left_exists, right_exists;
	public Change(int? left_index, int? right_index, T left, bool left_exists, T right, bool right_exists, bool same) {
		this.same = same;
		this.left_index = (left_exists) ? left_index : null;
		this.right_index = (right_exists) ? right_index : null;
		this.left = left; 
		this.right = right;
		this.left_exists = left_exists; 
		this.right_exists = right_exists;
		this.deleted = (!same && left_exists); 
		this.inserted = (!same && right_exists);
	}
}

static IEnumerable<Change<T>> FullDiff<T>(IEnumerable<T> input, IEnumerable<T> output) {
	var _input = input.ToArray();
	var _output = output.ToArray();
	return Report<T>( Diff.DiffT<T>(_input, _output), _input, _output);
}

IEnumerable<Change<T>> UniqueDiff<T>(IEnumerable<T> input, IEnumerable<T> output) {
	var _input = input.ToArray();
	var _output = output.ToArray();
	var union = _input.Union(_output);
	
	union.Dump();
	
//	return (from item in union
//	        let left_exists = _input.Contains(item)
//			let left_index = _input.E
//			let right_exists = _output.Contains(item)
//			select new Change<T>(
	
	return Report<T>( Diff.DiffT<T>(_input, _output), _input, _output);
}

static IEnumerable<Change<T>> Report<T>(Diff.Item[] items, T[] input, T[] output) {
  var StartA = 0;
  var StartB = 0;
  
  var q1 = from item_index in Enumerable.Range(0, items.Count())
  		   let item = items[item_index]
		   let last = item_index + 1 == items.Length
  		   let steps = Math.Max(item.deletedA, item.insertedB)
		   let NextA = item.StartA + item.deletedA
		   let NextB = item.StartB + item.insertedB
		   let Prev = (from i in Enumerable.Range(0, item.StartA - StartA) 
		   				let left_index = StartA + i
						let right_index = StartB + i
						let left = input[left_index]
						let right = output[right_index]
		   			   select new Change<T>(left_index, right_index, left, true, right, true, true))
		   let Diff = (from i in Enumerable.Range(0, steps) 
					  let left_index = item.StartA + i
					  let right_index = item.StartB + i
					  let left_exists = (i < item.deletedA)
					  let right_exists = (i < item.insertedB)
					  let left = (!left_exists) ? default(T) : input[left_index]
					  let right = (!right_exists) ? default(T) :  output[right_index]
		   			  select new Change<T>(left_index, right_index, left, left_exists, right, right_exists, false))
		   let Next = (from i in Enumerable.Range(0, input.Length - NextA) 
		   				let left_index = NextA + i
						let right_index = NextB + i
						let left = input[left_index]
						let right = output[right_index]
		   			   select new Change<T>(left_index, right_index, left, true, right, true, true))
		   let Finish = (last) ? Next : Enumerable.Empty<Change<T>>()
		   let Changes = Prev.Concat(Diff).Concat(Finish).ToArray()
		   select new { 
			 Changes,
			 nextStartA = (StartA = NextA),
			 nextStartB = (StartB = NextB),
			 last
		   };

  var q2 = (from item in q1
  		   from change in item.Changes
		   select change);
		   
  return q2;
}

IEnumerable<int> FromTo(int start, int end) {
  return Enumerable.Range(start, end - start);
}

void Test() {
	  StringBuilder ret = new StringBuilder();
	  string a, b;

	  System.Diagnostics.ConsoleTraceListener ctl = new System.Diagnostics.ConsoleTraceListener(false);
	  System.Diagnostics.Debug.Listeners.Add(ctl);

	  System.Console.WriteLine("Diff Self Test...");
	  
	  // test all changes
	  a = "a,b,c,d,e,f,g,h,i,j,k,l".Replace(',', '\n');
	  b = "0,1,2,3,4,5,6,7,8,9".Replace(',', '\n');
	  System.Diagnostics.Debug.Assert(TestHelper(Diff.DiffText(a, b, false, false, false))
		== "12.10.0.0*", 
		"all-changes test failed.");
	  System.Diagnostics.Debug.WriteLine("all-changes test passed.");
	  // test all same
	  a = "a,b,c,d,e,f,g,h,i,j,k,l".Replace(',', '\n');
	  b = a;
	  System.Diagnostics.Debug.Assert(TestHelper(Diff.DiffText(a, b, false, false, false))
		== "",
		"all-same test failed.");
	  System.Diagnostics.Debug.WriteLine("all-same test passed.");

	  // test snake
	  a = "a,b,c,d,e,f".Replace(',', '\n');
	  b = "b,c,d,e,f,x".Replace(',', '\n');
	  System.Diagnostics.Debug.Assert(TestHelper(Diff.DiffText(a, b, false, false, false))
		== "1.0.0.0*0.1.6.5*",
		"snake test failed.");
	  System.Diagnostics.Debug.WriteLine("snake test passed.");

	  // 2002.09.20 - repro
	  a = "c1,a,c2,b,c,d,e,g,h,i,j,c3,k,l".Replace(',', '\n');
	  b = "C1,a,C2,b,c,d,e,I1,e,g,h,i,j,C3,k,I2,l".Replace(',', '\n');
	  System.Diagnostics.Debug.Assert(TestHelper(Diff.DiffText(a, b, false, false, false))
		== "1.1.0.0*1.1.2.2*0.2.7.7*1.1.11.13*0.1.13.15*",
		"repro20020920 test failed.");
	  System.Diagnostics.Debug.WriteLine("repro20020920 test passed.");
	  
	  // 2003.02.07 - repro
	  a = "F".Replace(',', '\n');
	  b = "0,F,1,2,3,4,5,6,7".Replace(',', '\n');
	  System.Diagnostics.Debug.Assert(TestHelper(Diff.DiffText(a, b, false, false, false))
		== "0.1.0.0*0.7.1.2*", 
		"repro20030207 test failed.");
	  System.Diagnostics.Debug.WriteLine("repro20030207 test passed.");
	  
	  // Muegel - repro
	  a = "HELLO\nWORLD";
	  b = "\n\nhello\n\n\n\nworld\n";
	  System.Diagnostics.Debug.Assert(TestHelper(Diff.DiffText(a, b, false, false, false))
		== "2.8.0.0*", 
		"repro20030409 test failed.");
	  System.Diagnostics.Debug.WriteLine("repro20030409 test passed.");

	  // test some differences
	  a = "a,b,-,c,d,e,f,f".Replace(',', '\n');
	  b = "a,b,x,c,e,f".Replace(',', '\n');
	  System.Diagnostics.Debug.Assert(TestHelper(Diff.DiffText(a, b, false, false, false))
		== "1.1.2.2*1.0.4.4*1.0.7.6*", 
		"some-changes test failed.");
	  System.Diagnostics.Debug.WriteLine("some-changes test passed.");

	  // test one change within long chain of repeats
	  a = "a,a,a,a,a,a,a,a,a,a".Replace(',', '\n');
	  b = "a,a,a,a,-,a,a,a,a,a".Replace(',', '\n');
	  System.Diagnostics.Debug.Assert(TestHelper(Diff.DiffText(a, b, false, false, false))
		== "0.1.4.4*1.0.9.10*", 
		"long chain of repeats test failed.");

	  System.Diagnostics.Debug.WriteLine("End.");
	  System.Diagnostics.Debug.Flush();
}

public static string TestHelper(Diff.Item []f) {
  StringBuilder ret = new StringBuilder();
  for (int n = 0; n < f.Length; n++) {
	ret.Append(f[n].deletedA.ToString() + "." + f[n].insertedB.ToString() + "." + f[n].StartA.ToString() + "." + f[n].StartB.ToString() + "*");
  }
  // Debug.Write(5, "TestHelper", ret.ToString());
  return (ret.ToString());
}

public class Diff
  {

	/// <summary>details of one difference.</summary>
	public struct Item
	{
	  /// <summary>Start Line number in Data A.</summary>
	  public int StartA;
	  /// <summary>Start Line number in Data B.</summary>
	  public int StartB;

	  /// <summary>Number of changes in Data A.</summary>
	  public int deletedA;
	  /// <summary>Number of changes in Data B.</summary>
	  public int insertedB;
	} // Item

	/// <summary>
	/// Shortest Middle Snake Return Data
	/// </summary>
	private struct SMSRD
	{
	  internal int x, y;
	  // internal int u, v;  // 2002.09.20: no need for 2 points 
	}


	#region self-Test

#if (SELFTEST)
	/// <summary>
	/// start a self- / box-test for some diff cases and report to the debug output.
	/// </summary>
	/// <param name="args">not used</param>
	/// <returns>always 0</returns>
	public static int Main(string[] args) {

	}



#endif
	#endregion


	/// <summary>
	/// Find the difference in 2 texts, comparing by textlines.
	/// </summary>
	/// <param name="TextA">A-version of the text (usualy the old one)</param>
	/// <param name="TextB">B-version of the text (usualy the new one)</param>
	/// <returns>Returns a array of Items that describe the differences.</returns>
	public Item[] DiffText(string TextA, string TextB) {
	  return (DiffText(TextA, TextB, false, false, false));
	} // DiffText


	/// <summary>
	/// Find the difference in 2 text documents, comparing by textlines.
	/// The algorithm itself is comparing 2 arrays of numbers so when comparing 2 text documents
	/// each line is converted into a (hash) number. This hash-value is computed by storing all
	/// textlines into a common hashtable so i can find dublicates in there, and generating a 
	/// new number each time a new textline is inserted.
	/// </summary>
	/// <param name="TextA">A-version of the text (usualy the old one)</param>
	/// <param name="TextB">B-version of the text (usualy the new one)</param>
	/// <param name="trimSpace">When set to true, all leading and trailing whitespace characters are stripped out before the comparation is done.</param>
	/// <param name="ignoreSpace">When set to true, all whitespace characters are converted to a single space character before the comparation is done.</param>
	/// <param name="ignoreCase">When set to true, all characters are converted to their lowercase equivivalence before the comparation is done.</param>
	/// <returns>Returns a array of Items that describe the differences.</returns>
	public static Item[] DiffText(string TextA, string TextB, bool trimSpace, bool ignoreSpace, bool ignoreCase) {
	  // prepare the input-text and convert to comparable numbers.
	  Hashtable h = new Hashtable(TextA.Length + TextB.Length);

	  // The A-Version of the data (original data) to be compared.
	  DiffData DataA = new DiffData(DiffCodes(TextA, h, trimSpace, ignoreSpace, ignoreCase));

	  // The B-Version of the data (modified data) to be compared.
	  DiffData DataB = new DiffData(DiffCodes(TextB, h, trimSpace, ignoreSpace, ignoreCase));

	  h = null; // free up hashtable memory (maybe)

	  int MAX = DataA.Length + DataB.Length + 1;
	  /// vector for the (0,0) to (x,y) search
	  int[] DownVector = new int[2 * MAX + 2];
	  /// vector for the (u,v) to (N,M) search
	  int[] UpVector = new int[2 * MAX + 2];

	  LCS(DataA, 0, DataA.Length, DataB, 0, DataB.Length, DownVector, UpVector);

	  Optimize(DataA);
	  Optimize(DataB);
	  return CreateDiffs(DataA, DataB);
	} // DiffText

	public static Item[] DiffT<T>(T[] ListA, T[] ListB) {
	  // prepare the input-text and convert to comparable numbers.
	  Hashtable h = new Hashtable(ListA.Length + ListB.Length);

	  // The A-Version of the data (original data) to be compared.
	  DiffData DataA = new DiffData(DiffCodes(ListA, h));

	  // The B-Version of the data (modified data) to be compared.
	  DiffData DataB = new DiffData(DiffCodes(ListB, h));

	  h = null; // free up hashtable memory (maybe)

	  int MAX = DataA.Length + DataB.Length + 1;
	  /// vector for the (0,0) to (x,y) search
	  int[] DownVector = new int[2 * MAX + 2];
	  /// vector for the (u,v) to (N,M) search
	  int[] UpVector = new int[2 * MAX + 2];

	  LCS(DataA, 0, DataA.Length, DataB, 0, DataB.Length, DownVector, UpVector);

	  Optimize(DataA);
	  Optimize(DataB);
	  return CreateDiffs(DataA, DataB);
	} // DiffText	

	/// <summary>
	/// If a sequence of modified lines starts with a line that contains the same content
	/// as the line that appends the changes, the difference sequence is modified so that the
	/// appended line and not the starting line is marked as modified.
	/// This leads to more readable diff sequences when comparing text files.
	/// </summary>
	/// <param name="Data">A Diff data buffer containing the identified changes.</param>
	private static void Optimize(DiffData Data) {
	  int StartPos, EndPos;

	  StartPos = 0;
	  while (StartPos < Data.Length) {
		while ((StartPos < Data.Length) && (Data.modified[StartPos] == false))
		  StartPos++;
		EndPos = StartPos;
		while ((EndPos < Data.Length) && (Data.modified[EndPos] == true))
		  EndPos++;

		if ((EndPos < Data.Length) && (Data.data[StartPos] == Data.data[EndPos])) {
		  Data.modified[StartPos] = false;
		  Data.modified[EndPos] = true;
		} else {
		  StartPos = EndPos;
		} // if
	  } // while
	} // Optimize


	/// <summary>
	/// Find the difference in 2 arrays of integers.
	/// </summary>
	/// <param name="ArrayA">A-version of the numbers (usualy the old one)</param>
	/// <param name="ArrayB">B-version of the numbers (usualy the new one)</param>
	/// <returns>Returns a array of Items that describe the differences.</returns>
	public static Item[] DiffInt(int[] ArrayA, int[] ArrayB) {
	  // The A-Version of the data (original data) to be compared.
	  DiffData DataA = new DiffData(ArrayA);

	  // The B-Version of the data (modified data) to be compared.
	  DiffData DataB = new DiffData(ArrayB);

	  int MAX = DataA.Length + DataB.Length + 1;
	  /// vector for the (0,0) to (x,y) search
	  int[] DownVector = new int[2 * MAX + 2];
	  /// vector for the (u,v) to (N,M) search
	  int[] UpVector = new int[2 * MAX + 2];

	  LCS(DataA, 0, DataA.Length, DataB, 0, DataB.Length, DownVector, UpVector);
	  return CreateDiffs(DataA, DataB);
	} // Diff


	/// <summary>
	/// This function converts all textlines of the text into unique numbers for every unique textline
	/// so further work can work only with simple numbers.
	/// </summary>
	/// <param name="aText">the input text</param>
	/// <param name="h">This extern initialized hashtable is used for storing all ever used textlines.</param>
	/// <param name="trimSpace">ignore leading and trailing space characters</param>
	/// <returns>a array of integers.</returns>
	public static int[] DiffCodes<T>(T[] Lines) {
	  var h = new Hashtable();
	  return DiffCodes<T>(Lines, h);
	}
	
	public static int[] DiffCodes<T>(T[] Lines, Hashtable h) {
	  // get all codes of the text
	  int[] Codes;
	  int lastUsedCode = h.Count;
	  object aCode;
	  //string s;

	  // strip off all cr, only use lf as textline separator.
	  Codes = new int[Lines.Length];

	  for (int i = 0; i < Lines.Length; ++i) {
		var s = Lines[i];

		aCode = h[s];
		if (aCode == null) {
		  lastUsedCode++;
		  h[s] = lastUsedCode;
		  Codes[i] = lastUsedCode;
		} else {
		  Codes[i] = (int)aCode;
		} // if
	  } // for
	  return (Codes);
	} // DiffCodes

	/// <summary>
	/// This function converts all textlines of the text into unique numbers for every unique textline
	/// so further work can work only with simple numbers.
	/// </summary>
	/// <param name="aText">the input text</param>
	/// <param name="h">This extern initialized hashtable is used for storing all ever used textlines.</param>
	/// <param name="trimSpace">ignore leading and trailing space characters</param>
	/// <returns>a array of integers.</returns>
	private static int[] DiffCodes(string aText, Hashtable h, bool trimSpace, bool ignoreSpace, bool ignoreCase) {
	  // get all codes of the text
	  string[] Lines;
	  int[] Codes;
	  int lastUsedCode = h.Count;
	  object aCode;
	  string s;

	  // strip off all cr, only use lf as textline separator.
	  aText = aText.Replace("\r", "");
	  Lines = aText.Split('\n');

	  Codes = new int[Lines.Length];

	  for (int i = 0; i < Lines.Length; ++i) {
		s = Lines[i];
		if (trimSpace)
		  s = s.Trim();

		if (ignoreSpace) {
		  s = Regex.Replace(s, "\\s+", " ");            // TODO: optimization: faster blank removal.
		}

		if (ignoreCase)
		  s = s.ToLower();

		aCode = h[s];
		if (aCode == null) {
		  lastUsedCode++;
		  h[s] = lastUsedCode;
		  Codes[i] = lastUsedCode;
		} else {
		  Codes[i] = (int)aCode;
		} // if
	  } // for
	  return (Codes);
	} // DiffCodes


	/// <summary>
	/// This is the algorithm to find the Shortest Middle Snake (SMS).
	/// </summary>
	/// <param name="DataA">sequence A</param>
	/// <param name="LowerA">lower bound of the actual range in DataA</param>
	/// <param name="UpperA">upper bound of the actual range in DataA (exclusive)</param>
	/// <param name="DataB">sequence B</param>
	/// <param name="LowerB">lower bound of the actual range in DataB</param>
	/// <param name="UpperB">upper bound of the actual range in DataB (exclusive)</param>
	/// <param name="DownVector">a vector for the (0,0) to (x,y) search. Passed as a parameter for speed reasons.</param>
	/// <param name="UpVector">a vector for the (u,v) to (N,M) search. Passed as a parameter for speed reasons.</param>
	/// <returns>a MiddleSnakeData record containing x,y and u,v</returns>
	private static SMSRD SMS(DiffData DataA, int LowerA, int UpperA, DiffData DataB, int LowerB, int UpperB,
	  int[] DownVector, int[] UpVector) {

	  SMSRD ret;
	  int MAX = DataA.Length + DataB.Length + 1;

	  int DownK = LowerA - LowerB; // the k-line to start the forward search
	  int UpK = UpperA - UpperB; // the k-line to start the reverse search

	  int Delta = (UpperA - LowerA) - (UpperB - LowerB);
	  bool oddDelta = (Delta & 1) != 0;

	  // The vectors in the publication accepts negative indexes. the vectors implemented here are 0-based
	  // and are access using a specific offset: UpOffset UpVector and DownOffset for DownVektor
	  int DownOffset = MAX - DownK;
	  int UpOffset = MAX - UpK;

	  int MaxD = ((UpperA - LowerA + UpperB - LowerB) / 2) + 1;

	  // Debug.Write(2, "SMS", String.Format("Search the box: A[{0}-{1}] to B[{2}-{3}]", LowerA, UpperA, LowerB, UpperB));

	  // init vectors
	  DownVector[DownOffset + DownK + 1] = LowerA;
	  UpVector[UpOffset + UpK - 1] = UpperA;

	  for (int D = 0; D <= MaxD; D++) {

		// Extend the forward path.
		for (int k = DownK - D; k <= DownK + D; k += 2) {
		  // Debug.Write(0, "SMS", "extend forward path " + k.ToString());

		  // find the only or better starting point
		  int x, y;
		  if (k == DownK - D) {
			x = DownVector[DownOffset + k + 1]; // down
		  } else {
			x = DownVector[DownOffset + k - 1] + 1; // a step to the right
			if ((k < DownK + D) && (DownVector[DownOffset + k + 1] >= x))
			  x = DownVector[DownOffset + k + 1]; // down
		  }
		  y = x - k;

		  // find the end of the furthest reaching forward D-path in diagonal k.
		  while ((x < UpperA) && (y < UpperB) && (DataA.data[x] == DataB.data[y])) {
			x++; y++;
		  }
		  DownVector[DownOffset + k] = x;

		  // overlap ?
		  if (oddDelta && (UpK - D < k) && (k < UpK + D)) {
			if (UpVector[UpOffset + k] <= DownVector[DownOffset + k]) {
			  ret.x = DownVector[DownOffset + k];
			  ret.y = DownVector[DownOffset + k] - k;
			  // ret.u = UpVector[UpOffset + k];      // 2002.09.20: no need for 2 points 
			  // ret.v = UpVector[UpOffset + k] - k;
			  return (ret);
			} // if
		  } // if

		} // for k

		// Extend the reverse path.
		for (int k = UpK - D; k <= UpK + D; k += 2) {
		  // Debug.Write(0, "SMS", "extend reverse path " + k.ToString());

		  // find the only or better starting point
		  int x, y;
		  if (k == UpK + D) {
			x = UpVector[UpOffset + k - 1]; // up
		  } else {
			x = UpVector[UpOffset + k + 1] - 1; // left
			if ((k > UpK - D) && (UpVector[UpOffset + k - 1] < x))
			  x = UpVector[UpOffset + k - 1]; // up
		  } // if
		  y = x - k;

		  while ((x > LowerA) && (y > LowerB) && (DataA.data[x - 1] == DataB.data[y - 1])) {
			x--; y--; // diagonal
		  }
		  UpVector[UpOffset + k] = x;

		  // overlap ?
		  if (!oddDelta && (DownK - D <= k) && (k <= DownK + D)) {
			if (UpVector[UpOffset + k] <= DownVector[DownOffset + k]) {
			  ret.x = DownVector[DownOffset + k];
			  ret.y = DownVector[DownOffset + k] - k;
			  // ret.u = UpVector[UpOffset + k];     // 2002.09.20: no need for 2 points 
			  // ret.v = UpVector[UpOffset + k] - k;
			  return (ret);
			} // if
		  } // if

		} // for k

	  } // for D

	  throw new ApplicationException("the algorithm should never come here.");
	} // SMS


	/// <summary>
	/// This is the divide-and-conquer implementation of the longes common-subsequence (LCS) 
	/// algorithm.
	/// The published algorithm passes recursively parts of the A and B sequences.
	/// To avoid copying these arrays the lower and upper bounds are passed while the sequences stay constant.
	/// </summary>
	/// <param name="DataA">sequence A</param>
	/// <param name="LowerA">lower bound of the actual range in DataA</param>
	/// <param name="UpperA">upper bound of the actual range in DataA (exclusive)</param>
	/// <param name="DataB">sequence B</param>
	/// <param name="LowerB">lower bound of the actual range in DataB</param>
	/// <param name="UpperB">upper bound of the actual range in DataB (exclusive)</param>
	/// <param name="DownVector">a vector for the (0,0) to (x,y) search. Passed as a parameter for speed reasons.</param>
	/// <param name="UpVector">a vector for the (u,v) to (N,M) search. Passed as a parameter for speed reasons.</param>
	private static void LCS(DiffData DataA, int LowerA, int UpperA, DiffData DataB, int LowerB, int UpperB, int[] DownVector, int[] UpVector) {
	  // Debug.Write(2, "LCS", String.Format("Analyse the box: A[{0}-{1}] to B[{2}-{3}]", LowerA, UpperA, LowerB, UpperB));

	  // Fast walkthrough equal lines at the start
	  while (LowerA < UpperA && LowerB < UpperB && DataA.data[LowerA] == DataB.data[LowerB]) {
		LowerA++; LowerB++;
	  }

	  // Fast walkthrough equal lines at the end
	  while (LowerA < UpperA && LowerB < UpperB && DataA.data[UpperA - 1] == DataB.data[UpperB - 1]) {
		--UpperA; --UpperB;
	  }

	  if (LowerA == UpperA) {
		// mark as inserted lines.
		while (LowerB < UpperB)
		  DataB.modified[LowerB++] = true;

	  } else if (LowerB == UpperB) {
		// mark as deleted lines.
		while (LowerA < UpperA)
		  DataA.modified[LowerA++] = true;

	  } else {
		// Find the middle snakea and length of an optimal path for A and B
		SMSRD smsrd = SMS(DataA, LowerA, UpperA, DataB, LowerB, UpperB, DownVector, UpVector);
		// Debug.Write(2, "MiddleSnakeData", String.Format("{0},{1}", smsrd.x, smsrd.y));

		// The path is from LowerX to (x,y) and (x,y) to UpperX
		LCS(DataA, LowerA, smsrd.x, DataB, LowerB, smsrd.y, DownVector, UpVector);
		LCS(DataA, smsrd.x, UpperA, DataB, smsrd.y, UpperB, DownVector, UpVector);  // 2002.09.20: no need for 2 points 
	  }
	} // LCS()


	/// <summary>Scan the tables of which lines are inserted and deleted,
	/// producing an edit script in forward order.  
	/// </summary>
	/// dynamic array
	private static Item[] CreateDiffs(DiffData DataA, DiffData DataB) {
	  ArrayList a = new ArrayList();
	  Item aItem;
	  Item[] result;

	  int StartA, StartB;
	  int LineA, LineB;

	  LineA = 0;
	  LineB = 0;
	  while (LineA < DataA.Length || LineB < DataB.Length) {
		if ((LineA < DataA.Length) && (!DataA.modified[LineA])
		  && (LineB < DataB.Length) && (!DataB.modified[LineB])) {
		  // equal lines
		  LineA++;
		  LineB++;

		} else {
		  // maybe deleted and/or inserted lines
		  StartA = LineA;
		  StartB = LineB;

		  while (LineA < DataA.Length && (LineB >= DataB.Length || DataA.modified[LineA]))
			// while (LineA < DataA.Length && DataA.modified[LineA])
			LineA++;

		  while (LineB < DataB.Length && (LineA >= DataA.Length || DataB.modified[LineB]))
			// while (LineB < DataB.Length && DataB.modified[LineB])
			LineB++;

		  if ((StartA < LineA) || (StartB < LineB)) {
			// store a new difference-item
			aItem = new Item();
			aItem.StartA = StartA;
			aItem.StartB = StartB;
			aItem.deletedA = LineA - StartA;
			aItem.insertedB = LineB - StartB;
			a.Add(aItem);
		  } // if
		} // if
	  } // while

	  result = new Item[a.Count];
	  a.CopyTo(result);

	  return (result);
	}

  } // class Diff

  /// <summary>Data on one input file being compared.  
  /// </summary>
  internal class DiffData
  {

	/// <summary>Number of elements (lines).</summary>
	internal int Length;

	/// <summary>Buffer of numbers that will be compared.</summary>
	internal int[] data;

	/// <summary>
	/// Array of booleans that flag for modified data.
	/// This is the result of the diff.
	/// This means deletedA in the first Data or inserted in the second Data.
	/// </summary>
	internal bool[] modified;

	/// <summary>
	/// Initialize the Diff-Data buffer.
	/// </summary>
	/// <param name="data">reference to the buffer</param>
	internal DiffData(int[] initData) {
	  data = initData;
	  Length = initData.Length;
	  modified = new bool[Length + 2];
	} // DiffData

  } // class DiffData