using System;
using System.Collections;
using System.Text;
using System.Text.RegularExpressions;

namespace Mercury.Text
{
    /// <summary>
    /// Represents an implementation of an O(ND) difference algorithm.
    /// </summary>
    /// <remarks>
    /// This class implements the Difference Algorithm published in
    /// "An O(ND) Difference Algorithm and its Variations" by Eugene Myers
    /// Algorithmica Vol. 1 No. 2, 1986, p 251.  
    /// 
    /// There are many C, Java, Lisp implementations public available but they all seem to come
    /// from the same source (diffutils) that is under the (unfree) GNU public License
    /// and cannot be reused as a sourcecode for a commercial application.
    /// There are very old C implementations that use other (worse) algorithms.
    /// Microsoft also published sourcecode of a diff-tool (windiff) that uses some tree data.
    /// Also, a direct transfer from a C source to C# is not easy because there is a lot of pointer
    /// arithmetic in the typical C solutions and i need a managed solution.
    /// These are the reasons why I implemented the original published algorithm from the scratch and
    /// make it avaliable without the GNU license limitations.
    /// I do not need a high performance diff tool because it is used only sometimes.
    /// I will do some performace tweaking when needed.
    /// 
    /// The algorithm itself is comparing 2 arrays of numbers so when comparing 2 text documents
    /// each line is converted into a (hash) number. See DiffText(). 
    /// 
    /// Some chages to the original algorithm:
    /// The original algorithm was described using a recursive approach and comparing zero indexed arrays.
    /// Extracting sub-arrays and rejoining them is very performance and memory intensive so the same
    /// (readonly) data arrays are passed arround together with their lower and upper bounds.
    /// This circumstance makes the LCS and SMS functions more complicate.
    /// I added some code to the LCS function to get a fast response on sub-arrays that are identical,
    /// completely deleted or inserted.
    /// 
    /// The result from a comparisation is stored in 2 arrays that flag for modified (deleted or inserted)
    /// lines in the 2 data arrays. These bits are then analysed to produce a array of Item objects.
    /// 
    /// Further possible optimizations:
    /// (first rule: don't do it; second: don't do it yet)
    /// The arrays DataA and DataB are passed as parameters, but are never changed after the creation
    /// so they can be members of the class to avoid the paramter overhead.
    /// In SMS is a lot of boundary arithmetic in the for-D and for-k loops that can be done by increment
    /// and decrement of local variables.
    /// The DownVector and UpVector arrays are alywas created and destroyed each time the SMS gets called.
    /// It is possible to reuse tehm when transfering them to members of the class.
    /// See TODO: hints.
    /// 
    /// diff.cs: A port of the algorythm to C#
    /// 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
    /// 
    /// Changes:
    /// 2002.09.20 There was a "hang" in some situations.
    /// Now I undestand a little bit more of the SMS algorithm. 
    /// There have been overlapping boxes; that where analyzed partial differently.
    /// One return-point is enough.
    /// A assertion was added in CreateDiffs when in debug-mode, that counts the number of equal (no modified) lines in both arrays.
    /// They must be identical.
    /// 
    /// 2003.02.07 Out of bounds error in the Up/Down vector arrays in some situations.
    /// The two vetors are now accessed using different offsets that are adjusted using the start k-Line. 
    /// A test case is added. 
    /// 
    /// 2006.03.05 Some documentation and a direct Diff entry point.
    /// 
    /// 2006.03.08 Refactored the API to static methods on the Diff class to make usage simpler.
    /// 2006.03.10 using the standard Debug class for self-test now.
    ///            compile with: csc /target:exe /out:diffTest.exe /d:DEBUG /d:TRACE /d:SELFTEST Diff.cs
    /// 2007.01.06 license agreement changed to a BSD style license.
    /// 2007.06.03 added the Optimize method.
    /// 2007.09.23 UpVector and DownVector optimization by Jan Stoklasa ().
    /// 2008.05.31 Adjusted the testing code that failed because of the Optimize method (not a bug in the diff algorithm).
    /// 2008.10.08 Fixing a test case and adding a new test case.
    /// </remarks>
    public class Difference
    {
        #region Internal structures
        /// <summary>
        /// Tetails 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;
        }
        #endregion

        #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) {
            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();

            return (0);
        }


        public static string TestHelper(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());
        }
#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[] Calculate(string TextA, string TextB) {
            return (Calculate(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[] Calculate(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


        /// <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[] Calculate(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>
        /// <param name="ignoreSpace">Ignore blank spaces between characters.</param>
        /// <param name="ignoreCase">Case-insensitive.</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 snake 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="initData">reference to the buffer</param>
        internal DiffData(int[] initData) {
            data = initData;
            Length = initData.Length;
            modified = new bool[Length + 2];
        } // DiffData
    } // class DiffData

} // namespace