//*************************************************************************
/// <summary>
/// Private helper method which computes the differences on the bounded range
/// recursively.
/// </summary>
/// <returns>An array of the differences between the two input
/// sequences.</returns>
//*************************************************************************
private IDiffChange[] ComputeDiffRecursive(int originalStart, int originalEnd,
int modifiedStart, int modifiedEnd,
out bool quitEarly)
{
quitEarly = false;
// Find the start of the differences
while (originalStart <= originalEnd && modifiedStart <= modifiedEnd &&
ElementsAreEqual(originalStart, modifiedStart))
{
originalStart++;
modifiedStart++;
}
// Find the end of the differences
while (originalEnd >= originalStart && modifiedEnd >= modifiedStart &&
ElementsAreEqual(originalEnd, modifiedEnd))
{
originalEnd--;
modifiedEnd--;
}
// In the special case where we either have all insertions or all deletions or the sequences are identical
if (originalStart > originalEnd || modifiedStart > modifiedEnd)
{
IDiffChange[] changes;
if (modifiedStart <= modifiedEnd)
{
Debug.Assert(originalStart == originalEnd + 1, "originalStart should only be one more than originalEnd");
// All insertions
changes = new IDiffChange[1];
changes[0] = new DiffChange(originalStart, 0,
modifiedStart,
modifiedEnd - modifiedStart + 1);
}
else if (originalStart <= originalEnd)
{
Debug.Assert(modifiedStart == modifiedEnd + 1, "modifiedStart should only be one more than modifiedEnd");
// All deletions
changes = new IDiffChange[1];
changes[0] = new DiffChange(originalStart,
originalEnd - originalStart + 1,
modifiedStart, 0);
}
else
{
Debug.Assert(originalStart == originalEnd + 1, "originalStart should only be one more than originalEnd");
Debug.Assert(modifiedStart == modifiedEnd + 1, "modifiedStart should only be one more than modifiedEnd");
// Identical sequences - No differences
changes = Array.Empty <IDiffChange>();
}
return(changes);
}
// This problem can be solved using the Divide-And-Conquer technique.
int midOriginal, midModified;
IDiffChange[] result = ComputeRecursionPoint(originalStart, originalEnd, modifiedStart, modifiedEnd,
out midOriginal, out midModified, out quitEarly);
if (result != null)
{
// Result is not-null when there was enough memory to compute the changes while
// searching for the recursion point
return(result);
}
else if (!quitEarly)
{
// We can break the problem down recursively by finding the changes in the
// First Half: (originalStart, modifiedStart) to (midOriginal, midModified)
// Second Half: (midOriginal + 1, minModified + 1) to (originalEnd, modifiedEnd)
// NOTE: ComputeDiff() is inclusive, therefore the second range starts on the next point
IDiffChange[] leftChanges = ComputeDiffRecursive(originalStart, midOriginal, modifiedStart, midModified, out quitEarly);
IDiffChange[] rightChanges = Array.Empty <IDiffChange>();
if (!quitEarly)
{
rightChanges = ComputeDiffRecursive(midOriginal + 1, originalEnd, midModified + 1, modifiedEnd, out quitEarly);
}
else
{
// We did't have time to finish the first half, so we don't have time to compute this half.
// Consider the entire rest of the sequence different.
rightChanges = new DiffChange[]
{
new DiffChange(midOriginal + 1, originalEnd - (midOriginal + 1) + 1,
midModified + 1, modifiedEnd - (midModified + 1) + 1)
};
}
return(ConcatenateChanges(leftChanges, rightChanges));
}
// If we hit here, we quit early, and so can't return anything meaningful
return(new DiffChange[]
{
new DiffChange(originalStart, originalEnd - originalStart + 1,
modifiedStart, modifiedEnd - modifiedStart + 1)
});
}
//*************************************************************************
/// <summary>
/// Computes the differences between the given original and modified sequences.
/// </summary>
/// <param name="original">The original sequence.</param>
/// <param name="modified">The modified sequence.</param>
/// <param name="elementComparer">The diff element comparer.</param>
/// <returns>The set of differences between the sequences.</returns>
//*************************************************************************
public IDiffChange[] Diff(IList <T> original, IList <T> modified, IEqualityComparer <T> elementComparer,
ContinueDifferencePredicate <T> predicate)
{
Debug.Assert(original != null, "original is null");
Debug.Assert(modified != null, "modified is null");
Debug.Assert(elementComparer != null, "elementComparer is null");
m_original = original;
m_modified = modified;
m_elementComparer = elementComparer;
m_predicate = predicate;
m_originalIds = new int[OriginalSequence.Count];
m_modifiedIds = new int[ModifiedSequence.Count];
int originalStart = 0;
int originalEnd = OriginalSequence.Count - 1;
int modifiedStart = 0;
int modifiedEnd = ModifiedSequence.Count - 1;
// Find the start of the differences
while (originalStart <= originalEnd && modifiedStart <= modifiedEnd &&
ElementsAreEqual(originalStart, modifiedStart))
{
originalStart++;
modifiedStart++;
}
// Find the end of the differences
while (originalEnd >= originalStart && modifiedEnd >= modifiedStart &&
ElementsAreEqual(originalEnd, modifiedEnd))
{
originalEnd--;
modifiedEnd--;
}
// In the very special case where one of the ranges is negative
// Either the sequences are identical, or there is exactly one insertion
// or there is exactly one deletion. We have no need to compute the diffs.
if (originalStart > originalEnd || modifiedStart > modifiedEnd)
{
IDiffChange[] changes;
if (modifiedStart <= modifiedEnd)
{
Debug.Assert(originalStart == originalEnd + 1, "originalStart should only be one more than originalEnd");
// All insertions
changes = new IDiffChange[1];
changes[0] = new DiffChange(originalStart, 0,
modifiedStart,
modifiedEnd - modifiedStart + 1);
}
else if (originalStart <= originalEnd)
{
Debug.Assert(modifiedStart == modifiedEnd + 1, "modifiedStart should only be one more than modifiedEnd");
// All deletions
changes = new IDiffChange[1];
changes[0] = new DiffChange(originalStart,
originalEnd - originalStart + 1,
modifiedStart, 0);
}
else
{
Debug.Assert(originalStart == originalEnd + 1, "originalStart should only be one more than originalEnd");
Debug.Assert(modifiedStart == modifiedEnd + 1, "modifiedStart should only be one more than modifiedEnd");
// Identical sequences - No differences
changes = Array.Empty <IDiffChange>();
}
return(changes);
}
// Now that we have our bounds, calculate unique ids for all
// IDiffElements in the bounded range. That way, we speed up
// element comparisons during the diff computation.
ComputeUniqueIdentifiers(originalStart, originalEnd,
modifiedStart, modifiedEnd);
// Compute the diffences on the bounded range
return(ComputeDiff(originalStart, originalEnd,
modifiedStart, modifiedEnd));
}
//*************************************************************************
/// <summary>
/// Given the range to compute the diff on, this method finds the point:
/// (midOriginal, midModified)
/// that exists in the middle of the LCS of the two sequences and
/// is the point at which the LCS problem may be broken down recursively.
/// This method will try to keep the LCS trace in memory. If the LCS recursion
/// point is calculated and the full trace is available in memory, then this method
/// will return the change list.
/// </summary>
/// <param name="originalStart">The start bound of the original sequence range</param>
/// <param name="originalEnd">The end bound of the original sequence range</param>
/// <param name="modifiedStart">The start bound of the modified sequence range</param>
/// <param name="modifiedEnd">The end bound of the modified sequence range</param>
/// <param name="midOriginal">The middle point of the original sequence range</param>
/// <param name="midModified">The middle point of the modified sequence range</param>
/// <returns>The diff changes, if available, otherwise null</returns>
//*************************************************************************
private IDiffChange[] ComputeRecursionPoint(int originalStart, int originalEnd,
int modifiedStart, int modifiedEnd,
out int midOriginal, out int midModified,
out bool quitEarly)
{
int originalIndex, modifiedIndex;
int diagonalForwardStart = 0, diagonalForwardEnd = 0;
int diagonalReverseStart = 0, diagonalReverseEnd = 0;
int numDifferences;
// To traverse the edit graph and produce the proper LCS, our actual
// start position is just outside the given boundary
originalStart--;
modifiedStart--;
// We set these up to make the compiler happy, but they will
// be replaced before we return with the actual recursion point
midOriginal = 0;
midModified = 0;
// Clear out the history
m_forwardHistory.Clear();
m_reverseHistory.Clear();
// Each cell in the two arrays corresponds to a diagonal in the edit graph.
// The integer value in the cell represents the originalIndex of the furthest
// reaching point found so far that ends in that diagonal.
// The modifiedIndex can be computed mathematically from the originalIndex and the diagonal number.
int maxDifferences = (originalEnd - originalStart) + (modifiedEnd - modifiedStart);
int numDiagonals = maxDifferences + 1;
int[] forwardPoints = new int[numDiagonals];
int[] reversePoints = new int[numDiagonals];
// diagonalForwardBase: Index into forwardPoints of the diagonal which passes through (originalStart, modifiedStart)
// diagonalReverseBase: Index into reversePoints of the diagonal which passes through (originalEnd, modifiedEnd)
int diagonalForwardBase = (modifiedEnd - modifiedStart);
int diagonalReverseBase = (originalEnd - originalStart);
// diagonalForwardOffset: Geometric offset which allows modifiedIndex to be computed from originalIndex and the
// diagonal number (relative to diagonalForwardBase)
// diagonalReverseOffset: Geometric offset which allows modifiedIndex to be computed from originalIndex and the
// diagonal number (relative to diagonalReverseBase)
int diagonalForwardOffset = (originalStart - modifiedStart);
int diagonalReverseOffset = (originalEnd - modifiedEnd);
// delta: The difference between the end diagonal and the start diagonal. This is used to relate diagonal numbers
// relative to the start diagonal with diagonal numbers relative to the end diagonal.
// The Even/Oddn-ness of this delta is important for determining when we should check for overlap
int delta = diagonalReverseBase - diagonalForwardBase;
bool deltaIsEven = (delta % 2 == 0);
// Here we set up the start and end points as the furthest points found so far
// in both the forward and reverse directions, respectively
forwardPoints[diagonalForwardBase] = originalStart;
reversePoints[diagonalReverseBase] = originalEnd;
// Remember if we quit early, and thus need to do a best-effort result instead of a real result.
quitEarly = false;
// A couple of points:
// --With this method, we iterate on the number of differences between the two sequences.
// The more differences there actually are, the longer this will take.
// --Also, as the number of differences increases, we have to search on diagonals further
// away from the reference diagonal (which is diagonalForwardBase for forward, diagonalReverseBase for reverse).
// --We extend on even diagonals (relative to the reference diagonal) only when numDifferences
// is even and odd diagonals only when numDifferences is odd.
for (numDifferences = 1; numDifferences <= (maxDifferences / 2) + 1; numDifferences++)
{
int furthestOriginalIndex = 0;
int furthestModifiedIndex = 0;
// Run the algorithm in the forward direction
diagonalForwardStart = ClipDiagonalBound(diagonalForwardBase - numDifferences,
numDifferences,
diagonalForwardBase,
numDiagonals);
diagonalForwardEnd = ClipDiagonalBound(diagonalForwardBase + numDifferences,
numDifferences,
diagonalForwardBase,
numDiagonals);
for (int diagonal = diagonalForwardStart; diagonal <= diagonalForwardEnd; diagonal += 2)
{
// STEP 1: We extend the furthest reaching point in the present diagonal
// by looking at the diagonals above and below and picking the one whose point
// is further away from the start point (originalStart, modifiedStart)
if (diagonal == diagonalForwardStart || (diagonal < diagonalForwardEnd &&
forwardPoints[diagonal - 1] < forwardPoints[diagonal + 1]))
{
originalIndex = forwardPoints[diagonal + 1];
}
else
{
originalIndex = forwardPoints[diagonal - 1] + 1;
}
modifiedIndex = originalIndex - (diagonal - diagonalForwardBase) - diagonalForwardOffset;
// Save the current originalIndex so we can test for false overlap in step 3
int tempOriginalIndex = originalIndex;
// STEP 2: We can continue to extend the furthest reaching point in the present diagonal
// so long as the elements are equal.
while (originalIndex < originalEnd && modifiedIndex < modifiedEnd &&
ElementsAreEqual(originalIndex + 1, modifiedIndex + 1))
{
originalIndex++;
modifiedIndex++;
}
forwardPoints[diagonal] = originalIndex;
if (originalIndex + modifiedIndex > furthestOriginalIndex + furthestModifiedIndex)
{
furthestOriginalIndex = originalIndex;
furthestModifiedIndex = modifiedIndex;
}
// STEP 3: If delta is odd (overlap first happens on forward when delta is odd)
// and diagonal is in the range of reverse diagonals computed for numDifferences-1
// (the previous iteration; we havent computed reverse diagonals for numDifferences yet)
// then check for overlap.
if (!deltaIsEven && Math.Abs(diagonal - diagonalReverseBase) <= (numDifferences - 1))
{
if (originalIndex >= reversePoints[diagonal])
{
midOriginal = originalIndex;
midModified = modifiedIndex;
if (tempOriginalIndex <= reversePoints[diagonal] &&
MaxDifferencesHistory > 0 && numDifferences <= (MaxDifferencesHistory + 1))
{
// BINGO! We overlapped, and we have the full trace in memory!
goto WALKTRACE;
}
else
{
// Either false overlap, or we didn't have enough memory for the full trace
// Just return the recursion point
return(null);
}
}
}
}
// Check to see if we should be quitting early, before moving on to the next iteration.
int matchLengthOfLongest =
((furthestOriginalIndex - originalStart) + (furthestModifiedIndex - modifiedStart) - numDifferences) / 2;
if (ContinueDifferencePredicate != null &&
!ContinueDifferencePredicate(furthestOriginalIndex, OriginalSequence, matchLengthOfLongest))
{
// We can't finish, so skip ahead to generating a result from what we have.
quitEarly = true;
// Use the furthest distance we got in the forward direction.
midOriginal = furthestOriginalIndex;
midModified = furthestModifiedIndex;
if (matchLengthOfLongest > 0 && MaxDifferencesHistory > 0 && numDifferences <= (MaxDifferencesHistory + 1))
{
// Enough of the history is in memory to walk it backwards
goto WALKTRACE;
}
else
{
// We didn't actually remember enough of the history.
//Since we are quiting the diff early, we need to shift back the originalStart and modified start
//back into the boundary limits since we decremented their value above beyond the boundary limit.
originalStart++;
modifiedStart++;
return(new DiffChange[]
{
new DiffChange(originalStart, originalEnd - originalStart + 1,
modifiedStart, modifiedEnd - modifiedStart + 1)
});
}
}
// Run the algorithm in the reverse direction
diagonalReverseStart = ClipDiagonalBound(diagonalReverseBase - numDifferences,
numDifferences,
diagonalReverseBase,
numDiagonals);
diagonalReverseEnd = ClipDiagonalBound(diagonalReverseBase + numDifferences,
numDifferences,
diagonalReverseBase,
numDiagonals);
for (int diagonal = diagonalReverseStart; diagonal <= diagonalReverseEnd; diagonal += 2)
{
// STEP 1: We extend the furthest reaching point in the present diagonal
// by looking at the diagonals above and below and picking the one whose point
// is further away from the start point (originalEnd, modifiedEnd)
if (diagonal == diagonalReverseStart || (diagonal < diagonalReverseEnd &&
reversePoints[diagonal - 1] >= reversePoints[diagonal + 1]))
{
originalIndex = reversePoints[diagonal + 1] - 1;
}
else
{
originalIndex = reversePoints[diagonal - 1];
}
modifiedIndex = originalIndex - (diagonal - diagonalReverseBase) - diagonalReverseOffset;
// Save the current originalIndex so we can test for false overlap
int tempOriginalIndex = originalIndex;
// STEP 2: We can continue to extend the furthest reaching point in the present diagonal
// as long as the elements are equal.
while (originalIndex > originalStart && modifiedIndex > modifiedStart &&
ElementsAreEqual(originalIndex, modifiedIndex))
{
originalIndex--;
modifiedIndex--;
}
reversePoints[diagonal] = originalIndex;
// STEP 4: If delta is even (overlap first happens on reverse when delta is even)
// and diagonal is in the range of forward diagonals computed for numDifferences
// then check for overlap.
if (deltaIsEven && Math.Abs(diagonal - diagonalForwardBase) <= numDifferences)
{
if (originalIndex <= forwardPoints[diagonal])
{
midOriginal = originalIndex;
midModified = modifiedIndex;
if (tempOriginalIndex >= forwardPoints[diagonal] &&
MaxDifferencesHistory > 0 && numDifferences <= (MaxDifferencesHistory + 1))
{
// BINGO! We overlapped, and we have the full trace in memory!
goto WALKTRACE;
}
else
{
// Either false overlap, or we didn't have enough memory for the full trace
// Just return the recursion point
return(null);
}
}
}
}
// Save current vectors to history before the next iteration
if (numDifferences <= MaxDifferencesHistory)
{
// We are allocating space for one extra int, which we fill with
// the index of the diagonal base index
int[] temp = new int[diagonalForwardEnd - diagonalForwardStart + 2];
temp[0] = diagonalForwardBase - diagonalForwardStart + 1;
Array.Copy(forwardPoints, diagonalForwardStart, temp, 1, diagonalForwardEnd - diagonalForwardStart + 1);
m_forwardHistory.Add(temp);
temp = new int[diagonalReverseEnd - diagonalReverseStart + 2];
temp[0] = diagonalReverseBase - diagonalReverseStart + 1;
Array.Copy(reversePoints, diagonalReverseStart, temp, 1, diagonalReverseEnd - diagonalReverseStart + 1);
m_reverseHistory.Add(temp);
}
}
// If we got here, then we have the full trace in history. We just have to convert it to a change list
// NOTE: This part is a bit messy
WALKTRACE : IDiffChange[] forwardChanges, reverseChanges;
// First, walk backward through the forward diagonals history
using (DiffChangeHelper changeHelper = new DiffChangeHelper())
{
int diagonalMin = diagonalForwardStart;
int diagonalMax = diagonalForwardEnd;
int diagonalRelative = (midOriginal - midModified) - diagonalForwardOffset;
int lastOriginalIndex = Int32.MinValue;
int historyIndex = m_forwardHistory.Count - 1;
do
{
// Get the diagonal index from the relative diagonal number
int diagonal = diagonalRelative + diagonalForwardBase;
// Figure out where we came from
if (diagonal == diagonalMin || (diagonal < diagonalMax &&
forwardPoints[diagonal - 1] < forwardPoints[diagonal + 1]))
{
// Vertical line (the element is an insert)
originalIndex = forwardPoints[diagonal + 1];
modifiedIndex = originalIndex - diagonalRelative - diagonalForwardOffset;
if (originalIndex < lastOriginalIndex)
{
changeHelper.MarkNextChange();
}
lastOriginalIndex = originalIndex;
changeHelper.AddModifiedElement(originalIndex + 1, modifiedIndex);
diagonalRelative = (diagonal + 1) - diagonalForwardBase; //Setup for the next iteration
}
else
{
// Horizontal line (the element is a deletion)
originalIndex = forwardPoints[diagonal - 1] + 1;
modifiedIndex = originalIndex - diagonalRelative - diagonalForwardOffset;
if (originalIndex < lastOriginalIndex)
{
changeHelper.MarkNextChange();
}
lastOriginalIndex = originalIndex - 1;
changeHelper.AddOriginalElement(originalIndex, modifiedIndex + 1);
diagonalRelative = (diagonal - 1) - diagonalForwardBase; //Setup for the next iteration
}
if (historyIndex >= 0)
{
forwardPoints = m_forwardHistory[historyIndex];
diagonalForwardBase = forwardPoints[0]; //We stored this in the first spot
diagonalMin = 1;
diagonalMax = forwardPoints.Length - 1;
}
} while (--historyIndex >= -1);
// Ironically, we get the forward changes as the reverse of the
// order we added them since we technically added them backwards
forwardChanges = changeHelper.ReverseChanges;
}
if (quitEarly)
{
// Since we did quit early, assume everything after the midOriginal/midModified point is a diff
int originalStartPoint = midOriginal + 1;
int modifiedStartPoint = midModified + 1;
if (forwardChanges != null && forwardChanges.Length > 0)
{
IDiffChange lastForwardChange = forwardChanges[forwardChanges.Length - 1];
originalStartPoint = Math.Max(originalStartPoint, lastForwardChange.OriginalEnd);
modifiedStartPoint = Math.Max(modifiedStartPoint, lastForwardChange.ModifiedEnd);
}
reverseChanges = new DiffChange[]
{
new DiffChange(originalStartPoint, originalEnd - originalStartPoint + 1,
modifiedStartPoint, modifiedEnd - modifiedStartPoint + 1)
};
}
else
{
// Now walk backward through the reverse diagonals history
using (DiffChangeHelper changeHelper = new DiffChangeHelper())
{
int diagonalMin = diagonalReverseStart;
int diagonalMax = diagonalReverseEnd;
int diagonalRelative = (midOriginal - midModified) - diagonalReverseOffset;
int lastOriginalIndex = Int32.MaxValue;
int historyIndex = (deltaIsEven) ? m_reverseHistory.Count - 1
: m_reverseHistory.Count - 2;
do
{
// Get the diagonal index from the relative diagonal number
int diagonal = diagonalRelative + diagonalReverseBase;
// Figure out where we came from
if (diagonal == diagonalMin || (diagonal < diagonalMax &&
reversePoints[diagonal - 1] >= reversePoints[diagonal + 1]))
{
// Horizontal line (the element is a deletion))
originalIndex = reversePoints[diagonal + 1] - 1;
modifiedIndex = originalIndex - diagonalRelative - diagonalReverseOffset;
if (originalIndex > lastOriginalIndex)
{
changeHelper.MarkNextChange();
}
lastOriginalIndex = originalIndex + 1;
changeHelper.AddOriginalElement(originalIndex + 1, modifiedIndex + 1);
diagonalRelative = (diagonal + 1) - diagonalReverseBase; //Setup for the next iteration
}
else
{
// Vertical line (the element is an insertion)
originalIndex = reversePoints[diagonal - 1];
modifiedIndex = originalIndex - diagonalRelative - diagonalReverseOffset;
if (originalIndex > lastOriginalIndex)
{
changeHelper.MarkNextChange();
}
lastOriginalIndex = originalIndex;
changeHelper.AddModifiedElement(originalIndex + 1, modifiedIndex + 1);
diagonalRelative = (diagonal - 1) - diagonalReverseBase; //Setup for the next iteration
}
if (historyIndex >= 0)
{
reversePoints = m_reverseHistory[historyIndex];
diagonalReverseBase = reversePoints[0]; //We stored this in the first spot
diagonalMin = 1;
diagonalMax = reversePoints.Length - 1;
}
} while (--historyIndex >= -1);
// There are cases where the reverse history will find diffs that
// are correct, but not intuitive, so we need shift them.
reverseChanges = changeHelper.Changes;
}
}
return(ConcatenateChanges(forwardChanges, reverseChanges));
}
