public static void RunDiff(TextSection oldText, TextSection newText, RichTextBox rtb)
{
// Longest common subsequence, simple edition. If/when something faster is needed,
// should probably take a dependency on a proper diff package. Other than shorter
// comparison windows, other things to look for are avoiding creating strings here,
// working on the RichTextBox buffer directly for color, and unique'ing lines.
string[] oldLines = oldText.Lines;
string[] newLines = newText.Lines;
// Reduce strings to hashes.
int[] oldHashes = oldText.LineHashes;
int[] newHashes = newText.LineHashes;
// Reduce by trimming prefix and suffix.
int diffStart = 0;
while (diffStart < oldHashes.Length && diffStart < newHashes.Length && oldHashes[diffStart] == newHashes[diffStart])
{
diffStart++;
}
int newDiffEndExc = newLines.Length, oldDiffEndExc = oldLines.Length;
while (newDiffEndExc > diffStart && oldDiffEndExc > diffStart)
{
if (oldHashes[oldDiffEndExc - 1] == newHashes[newDiffEndExc - 1])
{
oldDiffEndExc--;
newDiffEndExc--;
}
else
{
break;
}
}
int suffixLength = (newLines.Length - newDiffEndExc);
// Build LCS table.
int oldLen = oldDiffEndExc - diffStart, newLen = newDiffEndExc - diffStart;
int[,] lcs = new int[oldLen + 1, newLen + 1]; // already zero-initialized
for (int i = 0; i < oldLen; i++)
{
for (int j = 0; j < newLen; j++)
{
if (oldHashes[i + diffStart] == newHashes[j + diffStart])
{
lcs[i + 1, j + 1] = lcs[i, j] + 1;
}
else
{
lcs[i + 1, j + 1] = Math.Max(lcs[i, j + 1], lcs[i + 1, j]);
}
}
}
// Print the diff - common prefix, backtracked diff and common suffix.
rtb.AppendLines(" ", newLines, 0, diffStart, Color.White);
{
int i = oldLen, j = newLen;
Stack <string> o = new Stack <string>();
for (;;)
{
if (i > 0 && j > 0 && oldHashes[diffStart + i - 1] == newHashes[diffStart + j - 1])
{
o.Push(" " + oldLines[diffStart + i - 1]);
i--;
j--;
}
else if (j > 0 && (i == 0 || lcs[i, j - 1] >= lcs[i - 1, j]))
{
o.Push("+ " + newLines[diffStart + j - 1]);
j--;
}
else if (i > 0 && (j == 0 || lcs[i, j - 1] < lcs[i - 1, j]))
{
o.Push("- " + oldLines[diffStart + i - 1]);
i--;
}
else
{
break;
}
}
while (o.Count != 0)
{
string line = o.Pop();
Color c = (line[0] == ' ') ? Color.White :
((line[0] == '+') ? Color.Yellow : Color.Red);
rtb.AppendLine(line, c);
}
}
rtb.AppendLines(" ", newLines, newDiffEndExc, (newLines.Length - newDiffEndExc), Color.White);
}
