} // 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 LongesCommonSequence( 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
SmsReturnData smsrd = ShortestMiddleSnake( 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
LongesCommonSequence( DataA, LowerA, smsrd.x, DataB, LowerB, smsrd.y, DownVector, UpVector );
LongesCommonSequence( DataA, smsrd.x, UpperA, DataB, smsrd.y, UpperB, DownVector, UpVector ); // 2002.09.20: no need for 2 points
}
} // LongesCommonSequence
/// <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( List<string> TextA, List<string> TextB, bool trimSpace, bool ignoreSpace, bool ignoreCase )
{
Hashtable codeHash = new Hashtable( TextA.Count + TextB.Count );
DiffData DataA = new DiffData( GenerateDiffCodes( TextA, codeHash, trimSpace, ignoreSpace, ignoreCase ) );
DiffData DataB = new DiffData( GenerateDiffCodes( TextB, codeHash, trimSpace, ignoreSpace, ignoreCase ) );
codeHash = null; // free up hashtable memory (maybe)
int combinedLength = DataA.Length + DataB.Length + 1;
/// vector for the (0,0) to (x,y) search
int[] DownVector = new int[2 * combinedLength + 2];
/// vector for the (u,v) to (N,M) search
int[] UpVector = new int[2 * combinedLength + 2];
LongesCommonSequence( DataA, 0, DataA.Length, DataB, 0, DataB.Length, DownVector, UpVector );
Optimize( DataA );
Optimize( DataB );
return CreateDiffs( DataA, DataB );
} // DiffText
} // 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
} // GenerateDiffCodes
/// <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 SmsReturnData ShortestMiddleSnake( DiffData DataA, int LowerA, int UpperA, DiffData DataB, int LowerB, int UpperB,
int[] DownVector, int[] UpVector )
{
SmsReturnData 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
