function DiffEngine::_compareseq

Find LCS of two sequences.

The results are recorded in the vectors $this->{x,y}changed[], by storing a 1 in the element for each line that is an insertion or deletion (ie. is not in the LCS).

The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.

Note that XLIM, YLIM are exclusive bounds. All line numbers are origin-0 and discarded lines are not counted.

File

core/lib/Drupal/Component/Diff/Engine/DiffEngine.php, line 283

Class

DiffEngine

Class used internally by Diff to actually compute the diffs.

Namespace

Code

protected function _compareseq($xoff, $xlim, $yoff, $ylim) {
    // Slide down the bottom initial diagonal.
    while ($xoff < $xlim && $yoff < $ylim && $this->xv[$xoff] == $this->yv[$yoff]) {
        ++$xoff;
        ++$yoff;
    }
    // Slide up the top initial diagonal.
    while ($xlim > $xoff && $ylim > $yoff && $this->xv[$xlim - 1] == $this->yv[$ylim - 1]) {
        --$xlim;
        --$ylim;
    }
    if ($xoff == $xlim || $yoff == $ylim) {
        $lcs = 0;
    }
    else {
        // This is ad hoc but seems to work well.
        
        //$nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);
        
        //$nchunks = max(2, min(8, (int)$nchunks));
        $nchunks = min(7, $xlim - $xoff, $ylim - $yoff) + 1;
        list($lcs, $seps) = $this->_diag($xoff, $xlim, $yoff, $ylim, $nchunks);
    }
    if ($lcs == 0) {
        // X and Y sequences have no common subsequence:
        // mark all changed.
        while ($yoff < $ylim) {
            $this->ychanged[$this->yind[$yoff++]] = 1;
        }
        while ($xoff < $xlim) {
            $this->xchanged[$this->xind[$xoff++]] = 1;
        }
    }
    else {
        // Use the partitions to split this problem into subproblems.
        reset($seps);
        $pt1 = $seps[0];
        while ($pt2 = next($seps)) {
            $this->_compareseq($pt1[0], $pt2[0], $pt1[1], $pt2[1]);
            $pt1 = $pt2;
        }
    }
}