Fix edge case in Diff.class.php causing it to error out

Previously it was possible for the startOffset and endOffset to overlap
for certain arrays, causing the algorithm to completely fall apart.

diff --git a/wcfsetup/install/files/lib/util/Diff.class.php b/wcfsetup/install/files/lib/util/Diff.class.php
index ca0bce8cf652fccfc96558f5c296aaea894e0faf..e09b939e63221a613a84f5ed8240efd5ca8e0822 100644 (file)
--- a/wcfsetup/install/files/lib/util/Diff.class.php
+++ b/wcfsetup/install/files/lib/util/Diff.class.php
@@ -83,7 +83,7 @@ class Diff {
                while ($offsetStart < $this->sizeA && $offsetStart < $this->sizeB && $this->a[$offsetStart] === $this->b[$offsetStart]) {
                        $offsetStart++;
                }
-               while ($offsetEnd < $this->sizeA && $offsetEnd < $this->sizeB && $this->a[$this->sizeA - 1 - $offsetEnd] === $this->b[$this->sizeB - 1 - $offsetEnd]) {
+               while ($offsetEnd < ($this->sizeA - $offsetStart) && $offsetEnd < ($this->sizeB - $offsetStart) && $this->a[$this->sizeA - 1 - $offsetEnd] === $this->b[$this->sizeB - 1 - $offsetEnd]) {
                        $offsetEnd++;
                }
                
@@ -108,6 +108,7 @@ class Diff {
                // add 1 to fit the line of zeroes at the top and at the left
                $tableHeight = $this->sizeA + 1 - $offsetStart - $offsetEnd;
                $tableWidth = $this->sizeB + 1 - $offsetStart - $offsetEnd;
+               
                $table = new \SplFixedArray($tableHeight);
                for ($i = 0; $i < $tableHeight; $i++) {
                        $table[$i] = new \SplFixedArray($tableWidth);
@@ -139,12 +140,12 @@ class Diff {
                $x = $this->sizeB - $offsetStart - $offsetEnd;
                $y = $this->sizeA - $offsetStart - $offsetEnd;
                $lcsLength = $table[$y][$x];
-               $i = 0;
                
                // allocate array of the length of the LCS
-               $lcs = new \SplFixedArray($table[$y][$x] + $offsetStart + $offsetEnd);
+               $lcs = new \SplFixedArray($lcsLength + $offsetStart + $offsetEnd);
                
                // until no more items are left in the LCS
+               $i = 0;
                while ($table[$y][$x] !== 0) {
                        // go to the very left of the current length
                        if ($table[$y][$x - 1] === $table[$y][$x]) {