_lcsPos example

$x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $chunk) / $nchunks);
            for (; $x < $x1; $x++) {
                $line = $flip ? $this->yv[$x] : $this->xv[$x];
                if (empty($ymatches[$line])) {
                    continue;
                }
                $matches = $ymatches[$line];
                reset($matches);
                while ($y = current($matches)) {
                    if (empty($this->in_seq[$y])) {
                        $k = $this->_lcsPos($y);
                        assert($k > 0);
                        $ymids[$k] = $ymids[$k - 1];
                        break;
                    }
                    next($matches);
                }
                while ($y = current($matches)) {
                    if ($y > $this->seq[$k - 1]) {
                        assert($y <= $this->seq[$k]);
                        /* Optimization: this is a common case: next match is * just replacing previous match. */