// SMS
/// <summary>
/// This is the divide-and-conquer implementation of the longest 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>
static void LCS <T>(DiffData <T> dataA, int lowerA, int upperA, DiffData <T> dataB, int lowerB, int upperB, int[] downVector, int[] upVector) where T : IEquatable <T>
{
// Fast walkthrough equal lines at the start
while (lowerA < upperA && lowerB < upperB && dataA.Data[lowerA].Equals(dataB.Data[lowerB]))
{
lowerA++;
lowerB++;
}
// Fast walkthrough equal lines at the end
while (lowerA < upperA && lowerB < upperB && dataA.Data[upperA - 1].Equals(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
}
}
/// <summary>Scan the tables of which lines are inserted and deleted,
/// producing an edit script in forward order.
/// </summary>
/// dynamic array
static IEnumerable <DiffHunk> CreateDiffs <T>(DiffData <T> baseData, DiffData <T> changedData)
{
int lineA = 0;
int lineB = 0;
while (lineA < baseData.Length || lineB < changedData.Length)
{
if (lineA < baseData.Length && !baseData.Modified[lineA] && lineB < changedData.Length && !changedData.Modified[lineB])
{
// equal lines
lineA++;
lineB++;
}
else
{
// maybe deleted and/or inserted lines
int startA = lineA;
int startB = lineB;
while (lineA < baseData.Length && (lineB >= changedData.Length || baseData.Modified[lineA]))
{
// while (LineA < DataA.Length && DataA.Modified[LineA])
lineA++;
}
while (lineB < changedData.Length && (lineA >= baseData.Length || changedData.Modified[lineB]))
{
// while (LineB < DataB.Length && DataB.Modified[LineB])
lineB++;
}
if (startA < lineA || startB < lineB)
{
// store a new difference-item
yield return(new DiffHunk(startA, startB, lineA - startA, lineB - startB));
}
// if
}
// if
}
// while
}
/// <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>
static SMSRD SMS <T>(DiffData <T> dataA, int lowerA, int upperA, DiffData <T> dataB, int lowerB, int upperB, int[] downVector, int[] upVector) where T : IEquatable <T>
{
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].Equals(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;
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].Equals(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;
return(ret);
}
// if
}
// if
}
// for k
}
// for D
throw new ApplicationException("the algorithm should never come here.");
}