Text_Diff_Engine_native::_diag( $xoff, $xlim, $yoff, $ylim, $nchunks )

159    function _diag ($xoff, $xlim, $yoff, $ylim, $nchunks)160    {161        $flip = false;162 163        if ($xlim - $xoff > $ylim - $yoff) {164            /* Things seems faster (I'm not sure I understand why) when the165             * shortest sequence is in X. */166            $flip = true;167            list ($xoff, $xlim, $yoff, $ylim)168                = array($yoff, $ylim, $xoff, $xlim);169        }170 171        if ($flip) {172            for ($i = $ylim - 1; $i >= $yoff; $i--) {173                $ymatches[$this->xv[$i]][] = $i;174            }175        } else {176            for ($i = $ylim - 1; $i >= $yoff; $i--) {177                $ymatches[$this->yv[$i]][] = $i;178            }179        }180 181        $this->lcs = 0;182        $this->seq[0]= $yoff - 1;183        $this->in_seq = array();184        $ymids[0] = array();185 186        $numer = $xlim - $xoff + $nchunks - 1;187        $x = $xoff;188        for ($chunk = 0; $chunk < $nchunks; $chunk++) {189            if ($chunk > 0) {190                for ($i = 0; $i <= $this->lcs; $i++) {191                    $ymids[$i][$chunk - 1] = $this->seq[$i];192                }193            }194 195            $x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $chunk) / $nchunks);196            for (; $x < $x1; $x++) {197                $line = $flip ? $this->yv[$x] : $this->xv[$x];198                if (empty($ymatches[$line])) {199                    continue;200                }201                $matches = $ymatches[$line];202                reset($matches);203                while ($y = current($matches)) {204                    if (empty($this->in_seq[$y])) {205                        $k = $this->_lcsPos($y);206                        assert($k > 0);207                        $ymids[$k] = $ymids[$k - 1];208                        break;209                    }210                    next($matches);211                }212                while ($y = current($matches)) {213                    if ($y > $this->seq[$k - 1]) {214                        assert($y <= $this->seq[$k]);215                        /* Optimization: this is a common case: next match is216                         * just replacing previous match. */217                        $this->in_seq[$this->seq[$k]] = false;218                        $this->seq[$k] = $y;219                        $this->in_seq[$y] = 1;220                    } elseif (empty($this->in_seq[$y])) {221                        $k = $this->_lcsPos($y);222                        assert($k > 0);223                        $ymids[$k] = $ymids[$k - 1];224                    }225                    next($matches);226                }227            }228        }229 230        $seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);231        $ymid = $ymids[$this->lcs];232        for ($n = 0; $n < $nchunks - 1; $n++) {233            $x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $n) / $nchunks);234            $y1 = $ymid[$n] + 1;235            $seps[] = $flip ? array($y1, $x1) : array($x1, $y1);236        }237        $seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);238