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Edit File : native.php \| Size : 15.52 KB
<?php /** * Class used internally by Text_Diff to actually compute the diffs. * * This class is implemented using native PHP code. * * The algorithm used here is mostly lifted from the perl module * Algorithm::Diff (version 1.06) by Ned Konz, which is available at: * http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip * * More ideas are taken from: http://www.ics.uci.edu/~eppstein/161/960229.html * * Some ideas (and a bit of code) are taken from analyze.c, of GNU * diffutils-2.7, which can be found at: * ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz * * Some ideas (subdivision by NCHUNKS > 2, and some optimizations) are from * Geoffrey T. Dairiki <dairiki@dairiki.org>. The original PHP version of this * code was written by him, and is used/adapted with his permission. * * Copyright 2004-2010 The Horde Project (http://www.horde.org/) * * See the enclosed file COPYING for license information (LGPL). If you did * not receive this file, see http://opensource.org/licenses/lgpl-license.php. * * @author Geoffrey T. Dairiki <dairiki@dairiki.org> * @package Text_Diff / class Text_Diff_Engine_native { function diff($from_lines, $to_lines) { array_walk($from_lines, array('Text_Diff', 'trimNewlines')); array_walk($to_lines, array('Text_Diff', 'trimNewlines')); $n_from = count($from_lines); $n_to = count($to_lines); $this->xchanged = $this->ychanged = array(); $this->xv = $this->yv = array(); $this->xind = $this->yind = array(); unset($this->seq); unset($this->in_seq); unset($this->lcs); // Skip leading common lines. for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) { if ($from_lines[$skip] !== $to_lines[$skip]) { break; } $this->xchanged[$skip] = $this->ychanged[$skip] = false; } // Skip trailing common lines. $xi = $n_from; $yi = $n_to; for ($endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++) { if ($from_lines[$xi] !== $to_lines[$yi]) { break; } $this->xchanged[$xi] = $this->ychanged[$yi] = false; } // Ignore lines which do not exist in both files. for ($xi = $skip; $xi < $n_from - $endskip; $xi++) { $xhash[$from_lines[$xi]] = 1; } for ($yi = $skip; $yi < $n_to - $endskip; $yi++) { $line = $to_lines[$yi]; if (($this->ychanged[$yi] = empty($xhash[$line]))) { continue; } $yhash[$line] = 1; $this->yv[] = $line; $this->yind[] = $yi; } for ($xi = $skip; $xi < $n_from - $endskip; $xi++) { $line = $from_lines[$xi]; if (($this->xchanged[$xi] = empty($yhash[$line]))) { continue; } $this->xv[] = $line; $this->xind[] = $xi; } // Find the LCS. $this->_compareseq(0, count($this->xv), 0, count($this->yv)); // Merge edits when possible. $this->_shiftBoundaries($from_lines, $this->xchanged, $this->ychanged); $this->_shiftBoundaries($to_lines, $this->ychanged, $this->xchanged); // Compute the edit operations. $edits = array(); $xi = $yi = 0; while ($xi < $n_from \|\| $yi < $n_to) { assert($yi < $n_to \|\| $this->xchanged[$xi]); assert($xi < $n_from \|\| $this->ychanged[$yi]); // Skip matching "snake". $copy = array(); while ($xi < $n_from && $yi < $n_to && !$this->xchanged[$xi] && !$this->ychanged[$yi]) { $copy[] = $from_lines[$xi++]; ++$yi; } if ($copy) { $edits[] = new Text_Diff_Op_copy($copy); } // Find deletes & adds. $delete = array(); while ($xi < $n_from && $this->xchanged[$xi]) { $delete[] = $from_lines[$xi++]; } $add = array(); while ($yi < $n_to && $this->ychanged[$yi]) { $add[] = $to_lines[$yi++]; } if ($delete && $add) { $edits[] = new Text_Diff_Op_change($delete, $add); } elseif ($delete) { $edits[] = new Text_Diff_Op_delete($delete); } elseif ($add) { $edits[] = new Text_Diff_Op_add($add); } } return $edits; } /* * Divides the Largest Common Subsequence (LCS) of the sequences (XOFF, * XLIM) and (YOFF, YLIM) into NCHUNKS approximately equally sized * segments. * * Returns (LCS, PTS). LCS is the length of the LCS. PTS is an array of * NCHUNKS+1 (X, Y) indexes giving the diving points between sub * sequences. The first sub-sequence is contained in (X0, X1), (Y0, Y1), * the second in (X1, X2), (Y1, Y2) and so on. Note that (X0, Y0) == * (XOFF, YOFF) and (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM). * * This function assumes that the first lines of the specified portions of * the two files do not match, and likewise that the last lines do not * match. The caller must trim matching lines from the beginning and end * of the portions it is going to specify. / function _diag ($xoff, $xlim, $yoff, $ylim, $nchunks) { $flip = false; if ($xlim - $xoff > $ylim - $yoff) { / Things seems faster (I'm not sure I understand why) when the * shortest sequence is in X. / $flip = true; list ($xoff, $xlim, $yoff, $ylim) = array($yoff, $ylim, $xoff, $xlim); } if ($flip) { for ($i = $ylim - 1; $i >= $yoff; $i--) { $ymatches[$this->xv[$i]][] = $i; } } else { for ($i = $ylim - 1; $i >= $yoff; $i--) { $ymatches[$this->yv[$i]][] = $i; } } $this->lcs = 0; $this->seq[0]= $yoff - 1; $this->in_seq = array(); $ymids[0] = array(); $numer = $xlim - $xoff + $nchunks - 1; $x = $xoff; for ($chunk = 0; $chunk < $nchunks; $chunk++) { if ($chunk > 0) { for ($i = 0; $i <= $this->lcs; $i++) { $ymids[$i][$chunk - 1] = $this->seq[$i]; } } $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. / $this->in_seq[$this->seq[$k]] = false; $this->seq[$k] = $y; $this->in_seq[$y] = 1; } elseif (empty($this->in_seq[$y])) { $k = $this->_lcsPos($y); assert($k > 0); $ymids[$k] = $ymids[$k - 1]; } next($matches); } } } $seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff); $ymid = $ymids[$this->lcs]; for ($n = 0; $n < $nchunks - 1; $n++) { $x1 = $xoff + (int)(($numer + ($xlim - $xoff) $n) / $nchunks); $y1 = $ymid[$n] + 1; $seps[] = $flip ? array($y1, $x1) : array($x1, $y1); } $seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim); return array($this->lcs, $seps); } function _lcsPos($ypos) { $end = $this->lcs; if ($end == 0 \|\| $ypos > $this->seq[$end]) { $this->seq[++$this->lcs] = $ypos; $this->in_seq[$ypos] = 1; return $this->lcs; } $beg = 1; while ($beg < $end) { $mid = (int)(($beg + $end) / 2); if ($ypos > $this->seq[$mid]) { $beg = $mid + 1; } else { $end = $mid; } } assert($ypos != $this->seq[$end]); $this->in_seq[$this->seq[$end]] = false; $this->seq[$end] = $ypos; $this->in_seq[$ypos] = 1; return $end; } /** * Finds LCS of two sequences. * * The results are recorded in the vectors $this->{x,y}changed[], by * storing a 1 in the element for each line that is an insertion or * deletion (ie. is not in the LCS). * * The subsequence of file 0 is (XOFF, XLIM) and likewise for file 1. * * Note that XLIM, YLIM are exclusive bounds. All line numbers are * origin-0 and discarded lines are not counted. / function _compareseq ($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 = $pt2; } } } /* * Adjusts inserts/deletes of identical lines to join changes as much as * possible. * * We do something when a run of changed lines include a line at one end * and has an excluded, identical line at the other. We are free to * choose which identical line is included. `compareseq' usually chooses * the one at the beginning, but usually it is cleaner to consider the * following identical line to be the "change". * * This is extracted verbatim from analyze.c (GNU diffutils-2.7). / function _shiftBoundaries($lines, &$changed, $other_changed) { $i = 0; $j = 0; assert(count($lines) == count($changed)); $len = count($lines); $other_len = count($other_changed); while (1) { / Scan forward to find the beginning of another run of * changes. Also keep track of the corresponding point in the * other file. * * Throughout this code, $i and $j are adjusted together so that * the first $i elements of $changed and the first $j elements of * $other_changed both contain the same number of zeros (unchanged * lines). * * Furthermore, $j is always kept so that $j == $other_len or * $other_changed[$j] == false. / while ($j < $other_len && $other_changed[$j]) { $j++; } while ($i < $len && ! $changed[$i]) { assert($j < $other_len && ! $other_changed[$j]); $i++; $j++; while ($j < $other_len && $other_changed[$j]) { $j++; } } if ($i == $len) { break; } $start = $i; / Find the end of this run of changes. / while (++$i < $len && $changed[$i]) { continue; } do { / Record the length of this run of changes, so that we can * later determine whether the run has grown. / $runlength = $i - $start; / Move the changed region back, so long as the previous * unchanged line matches the last changed one. This merges * with previous changed regions. / while ($start > 0 && $lines[$start - 1] == $lines[$i - 1]) { $changed[--$start] = 1; $changed[--$i] = false; while ($start > 0 && $changed[$start - 1]) { $start--; } assert($j > 0); while ($other_changed[--$j]) { continue; } assert($j >= 0 && !$other_changed[$j]); } / Set CORRESPONDING to the end of the changed run, at the * last point where it corresponds to a changed run in the * other file. CORRESPONDING == LEN means no such point has * been found. / $corresponding = $j < $other_len ? $i : $len; / Move the changed region forward, so long as the first * changed line matches the following unchanged one. This * merges with following changed regions. Do this second, so * that if there are no merges, the changed region is moved * forward as far as possible. / while ($i < $len && $lines[$start] == $lines[$i]) { $changed[$start++] = false; $changed[$i++] = 1; while ($i < $len && $changed[$i]) { $i++; } assert($j < $other_len && ! $other_changed[$j]); $j++; if ($j < $other_len && $other_changed[$j]) { $corresponding = $i; while ($j < $other_len && $other_changed[$j]) { $j++; } } } } while ($runlength != $i - $start); / If possible, move the fully-merged run of changes back to a * corresponding run in the other file. */ while ($corresponding < $i) { $changed[--$start] = 1; $changed[--$i] = 0; assert($j > 0); while ($other_changed[--$j]) { continue; } assert($j >= 0 && !$other_changed[$j]); } } } } Back

Edit File : native.php | Size : 15.52 KB

<?php
/**
 * Class used internally by Text_Diff to actually compute the diffs.
 *
 * This class is implemented using native PHP code.
 *
 * The algorithm used here is mostly lifted from the perl module
 * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
 * http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
 *
 * More ideas are taken from: http://www.ics.uci.edu/~eppstein/161/960229.html
 *
 * Some ideas (and a bit of code) are taken from analyze.c, of GNU
 * diffutils-2.7, which can be found at:
 * ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
 *
 * Some ideas (subdivision by NCHUNKS > 2, and some optimizations) are from
 * Geoffrey T. Dairiki <dairiki@dairiki.org>. The original PHP version of this
 * code was written by him, and is used/adapted with his permission.
 *
 * Copyright 2004-2010 The Horde Project (http://www.horde.org/)
 *
 * See the enclosed file COPYING for license information (LGPL). If you did
 * not receive this file, see http://opensource.org/licenses/lgpl-license.php.
 *
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 * @package Text_Diff
 */
class Text_Diff_Engine_native {

function diff($from_lines, $to_lines)
    {
        array_walk($from_lines, array('Text_Diff', 'trimNewlines'));
        array_walk($to_lines, array('Text_Diff', 'trimNewlines'));

$n_from = count($from_lines);
        $n_to = count($to_lines);

$this->xchanged = $this->ychanged = array();
        $this->xv = $this->yv = array();
        $this->xind = $this->yind = array();
        unset($this->seq);
        unset($this->in_seq);
        unset($this->lcs);

// Skip leading common lines.
        for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) {
            if ($from_lines[$skip] !== $to_lines[$skip]) {
                break;
            }
            $this->xchanged[$skip] = $this->ychanged[$skip] = false;
        }

// Skip trailing common lines.
        $xi = $n_from; $yi = $n_to;
        for ($endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++) {
            if ($from_lines[$xi] !== $to_lines[$yi]) {
                break;
            }
            $this->xchanged[$xi] = $this->ychanged[$yi] = false;
        }

// Ignore lines which do not exist in both files.
        for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
            $xhash[$from_lines[$xi]] = 1;
        }
        for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {
            $line = $to_lines[$yi];
            if (($this->ychanged[$yi] = empty($xhash[$line]))) {
                continue;
            }
            $yhash[$line] = 1;
            $this->yv[] = $line;
            $this->yind[] = $yi;
        }
        for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
            $line = $from_lines[$xi];
            if (($this->xchanged[$xi] = empty($yhash[$line]))) {
                continue;
            }
            $this->xv[] = $line;
            $this->xind[] = $xi;
        }

// Find the LCS.
        $this->_compareseq(0, count($this->xv), 0, count($this->yv));

// Merge edits when possible.
        $this->_shiftBoundaries($from_lines, $this->xchanged, $this->ychanged);
        $this->_shiftBoundaries($to_lines, $this->ychanged, $this->xchanged);

// Compute the edit operations.
        $edits = array();
        $xi = $yi = 0;
        while ($xi < $n_from || $yi < $n_to) {
            assert($yi < $n_to || $this->xchanged[$xi]);
            assert($xi < $n_from || $this->ychanged[$yi]);

// Skip matching "snake".
            $copy = array();
            while ($xi < $n_from && $yi < $n_to
                   && !$this->xchanged[$xi] && !$this->ychanged[$yi]) {
                $copy[] = $from_lines[$xi++];
                ++$yi;
            }
            if ($copy) {
                $edits[] = new Text_Diff_Op_copy($copy);
            }

// Find deletes & adds.
            $delete = array();
            while ($xi < $n_from && $this->xchanged[$xi]) {
                $delete[] = $from_lines[$xi++];
            }

$add = array();
            while ($yi < $n_to && $this->ychanged[$yi]) {
                $add[] = $to_lines[$yi++];
            }

if ($delete && $add) {
                $edits[] = new Text_Diff_Op_change($delete, $add);
            } elseif ($delete) {
                $edits[] = new Text_Diff_Op_delete($delete);
            } elseif ($add) {
                $edits[] = new Text_Diff_Op_add($add);
            }
        }

return $edits;
    }

/**
     * Divides the Largest Common Subsequence (LCS) of the sequences (XOFF,
     * XLIM) and (YOFF, YLIM) into NCHUNKS approximately equally sized
     * segments.
     *
     * Returns (LCS, PTS).  LCS is the length of the LCS. PTS is an array of
     * NCHUNKS+1 (X, Y) indexes giving the diving points between sub
     * sequences.  The first sub-sequence is contained in (X0, X1), (Y0, Y1),
     * the second in (X1, X2), (Y1, Y2) and so on.  Note that (X0, Y0) ==
     * (XOFF, YOFF) and (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
     *
     * This function assumes that the first lines of the specified portions of
     * the two files do not match, and likewise that the last lines do not
     * match.  The caller must trim matching lines from the beginning and end
     * of the portions it is going to specify.
     */
    function _diag ($xoff, $xlim, $yoff, $ylim, $nchunks)
    {
        $flip = false;

if ($xlim - $xoff > $ylim - $yoff) {
            /* Things seems faster (I'm not sure I understand why) when the
             * shortest sequence is in X. */
            $flip = true;
            list ($xoff, $xlim, $yoff, $ylim)
                = array($yoff, $ylim, $xoff, $xlim);
        }

if ($flip) {
            for ($i = $ylim - 1; $i >= $yoff; $i--) {
                $ymatches[$this->xv[$i]][] = $i;
            }
        } else {
            for ($i = $ylim - 1; $i >= $yoff; $i--) {
                $ymatches[$this->yv[$i]][] = $i;
            }
        }

$this->lcs = 0;
        $this->seq[0]= $yoff - 1;
        $this->in_seq = array();
        $ymids[0] = array();

$numer = $xlim - $xoff + $nchunks - 1;
        $x = $xoff;
        for ($chunk = 0; $chunk < $nchunks; $chunk++) {
            if ($chunk > 0) {
                for ($i = 0; $i <= $this->lcs; $i++) {
                    $ymids[$i][$chunk - 1] = $this->seq[$i];
                }
            }

$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. */
                        $this->in_seq[$this->seq[$k]] = false;
                        $this->seq[$k] = $y;
                        $this->in_seq[$y] = 1;
                    } elseif (empty($this->in_seq[$y])) {
                        $k = $this->_lcsPos($y);
                        assert($k > 0);
                        $ymids[$k] = $ymids[$k - 1];
                    }
                    next($matches);
                }
            }
        }

$seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);
        $ymid = $ymids[$this->lcs];
        for ($n = 0; $n < $nchunks - 1; $n++) {
            $x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $n) / $nchunks);
            $y1 = $ymid[$n] + 1;
            $seps[] = $flip ? array($y1, $x1) : array($x1, $y1);
        }
        $seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);

return array($this->lcs, $seps);
    }

function _lcsPos($ypos)
    {
        $end = $this->lcs;
        if ($end == 0 || $ypos > $this->seq[$end]) {
            $this->seq[++$this->lcs] = $ypos;
            $this->in_seq[$ypos] = 1;
            return $this->lcs;
        }

$beg = 1;
        while ($beg < $end) {
            $mid = (int)(($beg + $end) / 2);
            if ($ypos > $this->seq[$mid]) {
                $beg = $mid + 1;
            } else {
                $end = $mid;
            }
        }

assert($ypos != $this->seq[$end]);

$this->in_seq[$this->seq[$end]] = false;
        $this->seq[$end] = $ypos;
        $this->in_seq[$ypos] = 1;
        return $end;
    }

/**
     * Finds LCS of two sequences.
     *
     * The results are recorded in the vectors $this->{x,y}changed[], by
     * storing a 1 in the element for each line that is an insertion or
     * deletion (ie. is not in the LCS).
     *
     * The subsequence of file 0 is (XOFF, XLIM) and likewise for file 1.
     *
     * Note that XLIM, YLIM are exclusive bounds.  All line numbers are
     * origin-0 and discarded lines are not counted.
     */
    function _compareseq ($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;
            }
        }
    }

/**
     * Adjusts inserts/deletes of identical lines to join changes as much as
     * possible.
     *
     * We do something when a run of changed lines include a line at one end
     * and has an excluded, identical line at the other.  We are free to
     * choose which identical line is included.  `compareseq' usually chooses
     * the one at the beginning, but usually it is cleaner to consider the
     * following identical line to be the "change".
     *
     * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
     */
    function _shiftBoundaries($lines, &$changed, $other_changed)
    {
        $i = 0;
        $j = 0;

assert(count($lines) == count($changed));
        $len = count($lines);
        $other_len = count($other_changed);

while (1) {
            /* Scan forward to find the beginning of another run of
             * changes. Also keep track of the corresponding point in the
             * other file.
             *
             * Throughout this code, $i and $j are adjusted together so that
             * the first $i elements of $changed and the first $j elements of
             * $other_changed both contain the same number of zeros (unchanged
             * lines).
             *
             * Furthermore, $j is always kept so that $j == $other_len or
             * $other_changed[$j] == false. */
            while ($j < $other_len && $other_changed[$j]) {
                $j++;
            }

while ($i < $len && ! $changed[$i]) {
                assert($j < $other_len && ! $other_changed[$j]);
                $i++; $j++;
                while ($j < $other_len && $other_changed[$j]) {
                    $j++;
                }
            }

if ($i == $len) {
                break;
            }

$start = $i;

/* Find the end of this run of changes. */
            while (++$i < $len && $changed[$i]) {
                continue;
            }

do {
                /* Record the length of this run of changes, so that we can
                 * later determine whether the run has grown. */
                $runlength = $i - $start;

/* Move the changed region back, so long as the previous
                 * unchanged line matches the last changed one.  This merges
                 * with previous changed regions. */
                while ($start > 0 && $lines[$start - 1] == $lines[$i - 1]) {
                    $changed[--$start] = 1;
                    $changed[--$i] = false;
                    while ($start > 0 && $changed[$start - 1]) {
                        $start--;
                    }
                    assert($j > 0);
                    while ($other_changed[--$j]) {
                        continue;
                    }
                    assert($j >= 0 && !$other_changed[$j]);
                }

/* Set CORRESPONDING to the end of the changed run, at the
                 * last point where it corresponds to a changed run in the
                 * other file. CORRESPONDING == LEN means no such point has
                 * been found. */
                $corresponding = $j < $other_len ? $i : $len;

/* Move the changed region forward, so long as the first
                 * changed line matches the following unchanged one.  This
                 * merges with following changed regions.  Do this second, so
                 * that if there are no merges, the changed region is moved
                 * forward as far as possible. */
                while ($i < $len && $lines[$start] == $lines[$i]) {
                    $changed[$start++] = false;
                    $changed[$i++] = 1;
                    while ($i < $len && $changed[$i]) {
                        $i++;
                    }

assert($j < $other_len && ! $other_changed[$j]);
                    $j++;
                    if ($j < $other_len && $other_changed[$j]) {
                        $corresponding = $i;
                        while ($j < $other_len && $other_changed[$j]) {
                            $j++;
                        }
                    }
                }
            } while ($runlength != $i - $start);

/* If possible, move the fully-merged run of changes back to a
             * corresponding run in the other file. */
            while ($corresponding < $i) {
                $changed[--$start] = 1;
                $changed[--$i] = 0;
                assert($j > 0);
                while ($other_changed[--$j]) {
                    continue;
                }
                assert($j >= 0 && !$other_changed[$j]);
            }
        }
    }

}

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