xoopscube/altsys

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xoops_trust_path/libs/altsys/include/Text_Diff.php

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<?php
/**
 *  @brief XCL/PHP7 @gigamaster replace 'each' (deprecated) with foreach
 *
 * Text_Diff
 *
 * General API for generating and formatting diffs - the differences between
 * two sequences of strings.
 *
 * The PHP diff code used in this package was originally written by Geoffrey
 * T. Dairiki and is used with his permission.
 *
 * $Horde: framework/Text_Diff/Diff.php,v 1.13 2005/05/26 20:26:06 selsky Exp $
 *
 * @package Text_Diff
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 */
class Text_Diff {

    /**
     * Array of changes.
     *
     * @var array
     */
    public $_edits;

    /**
     * Computes diffs between sequences of strings.
     *
     * @param array $from_lines An array of strings.  Typically these are
     *                           lines from a file.
     * @param array $to_lines An array of strings.
     */
//HACK by domifara
//    function Text_Diff($from_lines, $to_lines)
    public function __construct( $from_lines, $to_lines ) {
        array_walk( $from_lines, [ $this, '_trimNewlines' ] );
        array_walk( $to_lines, [ $this, '_trimNewlines' ] );

        if ( extension_loaded( 'xdiff' ) ) {
            $engine = new Text_Diff_Engine_xdiff();
        } else {
            $engine = new Text_Diff_Engine_native();
        }

        $this->_edits = $engine->diff( $from_lines, $to_lines );
    }

    /**
     * Returns the array of differences.
     */
    public function getDiff() {
        return $this->_edits;
    }

    /**
     * Computes a reversed diff.
     *
     * Example:
     * <code>
     * $diff = new Text_Diff($lines1, $lines2);
     * $rev = $diff->reverse();
     * </code>
     *
     * @return Text_Diff  A Diff object representing the inverse of the
     *                    original diff.  Note that we purposely don't return a
     *                    reference here, since this essentially is a clone()
     *                    method.
     */
    public function reverse() {
        if ( version_compare( zend_version(), '2', '>' ) ) {
            $rev = clone( $obj );
        } else {
            $rev = $this;
        }
        $rev->_edits = [];
        foreach ( $this->_edits as $edit ) {
            $rev->_edits[] = $edit->reverse();
        }

        return $rev;
    }

    /**
     * Checks for an empty diff.
     *
     * @return bool  True if two sequences were identical.
     */
    public function isEmpty() {
        foreach ( $this->_edits as $edit ) {
            if ( ! is_a( $edit, 'Text_Diff_Op_copy' ) ) {
                return false;
            }
        }

        return true;
    }

    /**
     * Computes the length of the Longest Common Subsequence (LCS).
     *
     * This is mostly for diagnostic purposes.
     *
     * @return int  The length of the LCS.
     */
    public function lcs() {
        $lcs = 0;
        foreach ( $this->_edits as $edit ) {
            if ( is_a( $edit, 'Text_Diff_Op_copy' ) ) {
                $lcs += count( $edit->orig );
            }
        }

        return $lcs;
    }

    /**
     * Gets the original set of lines.
     *
     * This reconstructs the $from_lines parameter passed to the constructor.
     *
     * @return array  The original sequence of strings.
     */
    public function getOriginal() {
        $lines = [];
        foreach ( $this->_edits as $edit ) {
            if ( $edit->orig ) {
                array_splice( $lines, count( $lines ), 0, $edit->orig );
            }
        }

        return $lines;
    }

    /**
     * Gets the final set of lines.
     *
     * This reconstructs the $to_lines parameter passed to the constructor.
     *
     * @return array  The sequence of strings.
     */
    public function getFinal() {
        $lines = [];
        foreach ( $this->_edits as $edit ) {
            if ( $edit->final ) {
                array_splice( $lines, count( $lines ), 0, $edit->final );
            }
        }

        return $lines;
    }

    /**
     * Removes trailing newlines from a line of text. This is meant to be used
     * with array_walk().
     *
     * @param string $line The line to trim.
     * @param int $key The index of the line in the array. Not used.
     */
    public function _trimNewlines( &$line, $key ) {
        $line = str_replace( [ "\n", "\r" ], '', $line );
    }

    /**
     * Checks a diff for validity.
     *
     * This is here only for debugging purposes.
     *
     * @param $from_lines
     * @param $to_lines
     *
     * @return bool
     */
    public function _check( $from_lines, $to_lines ) {
        if ( serialize( $from_lines ) != serialize( $this->getOriginal() ) ) {
            trigger_error( "Reconstructed original doesn't match", E_USER_ERROR );
        }
        if ( serialize( $to_lines ) != serialize( $this->getFinal() ) ) {
            trigger_error( "Reconstructed final doesn't match", E_USER_ERROR );
        }

        $rev = $this->reverse();
        if ( serialize( $to_lines ) != serialize( $rev->getOriginal() ) ) {
            trigger_error( "Reversed original doesn't match", E_USER_ERROR );
        }
        if ( serialize( $from_lines ) != serialize( $rev->getFinal() ) ) {
            trigger_error( "Reversed final doesn't match", E_USER_ERROR );
        }

        $prevtype = null;
        foreach ( $this->_edits as $edit ) {
            if ( $prevtype == get_class( $edit ) ) {
                trigger_error( 'Edit sequence is non-optimal', E_USER_ERROR );
            }
            $prevtype = get_class( $edit );
        }

        return true;
    }
}

/**
 * $Horde: framework/Text_Diff/Diff.php,v 1.13 2005/05/26 20:26:06 selsky Exp $
 *
 * @package Text_Diff
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 */
class Text_MappedDiff extends Text_Diff {

    /**
     * Computes a diff between sequences of strings.
     *
     * This can be used to compute things like case-insensitve diffs, or diffs
     * which ignore changes in white-space.
     *
     * @param array $from_lines An array of strings.
     * @param array $to_lines An array of strings.
     * @param array $mapped_from_lines This array should have the same size
     *                                  number of elements as $from_lines.  The
     *                                  elements in $mapped_from_lines and
     *                                  $mapped_to_lines are what is actually
     *                                  compared when computing the diff.
     * @param array $mapped_to_lines This array should have the same number
     *                                  of elements as $to_lines.
     */

    public function __construct(
        $from_lines,
        $to_lines,
        $mapped_from_lines,
        $mapped_to_lines
    ) {
        assert( count( $from_lines ) == count( $mapped_from_lines ) );
        assert( count( $to_lines ) == count( $mapped_to_lines ) );

        parent::Text_Diff( $mapped_from_lines, $mapped_to_lines );

        $xi = $yi = 0;
        for ( $i = 0; $i < count( $this->_edits ); $i ++ ) {
            $orig = &$this->_edits[ $i ]->orig;
            if ( is_array( $orig ) ) {
                $orig = array_slice( $from_lines, $xi, count( $orig ) );
                $xi   += count( $orig );
            }

            $final = &$this->_edits[ $i ]->final;
            if ( is_array( $final ) ) {
                $final = array_slice( $to_lines, $yi, count( $final ) );
                $yi    += count( $final );
            }
        }
    }
}

/**
 * Class used internally by Diff to actually compute the diffs.  This class
 * uses the xdiff PECL package (https://pecl.php.net/package/xdiff) to compute
 * the differences between the two input arrays.
 *
 * @author  Jon Parise <jon@horde.org>
 * @package Text_Diff
 *
 * @access private
 */
class Text_Diff_Engine_xdiff {
    /**
     * @param $from_lines
     * @param $to_lines
     *
     * @return array
     */

    public function diff( $from_lines, $to_lines ) {
        /* Convert the two input arrays into strings for xdiff processing. */
        $from_string = implode( "\n", $from_lines );
        $to_string   = implode( "\n", $to_lines );

        /* Diff the two strings and convert the result to an array. */
        $diff = xdiff_string_diff( $from_string, $to_string, count( $to_lines ) );
        $diff = explode( "\n", $diff );

        /* Walk through the diff one line at a time.  We build the $edits
         * array of diff operations by reading the first character of the
         * xdiff output (which is in the "unified diff" format).
         *
         * Note that we don't have enough information to detect "changed"
         * lines using this approach, so we can't add Text_Diff_Op_changed
         * instances to the $edits array.  The result is still perfectly
         * valid, albeit a little less descriptive and efficient. */
        $edits = [];
        foreach ( $diff as $line ) {
            switch ( $line[0] ) {
                case ' ':
                    $edits[] = new Text_Diff_Op_copy( [ mb_substr( $line, 1 ) ] );
                    break;
                case '+':
                    $edits[] = new Text_Diff_Op_add( [ mb_substr( $line, 1 ) ] );
                    break;
                case '-':
                    $edits[] = new Text_Diff_Op_delete( [ mb_substr( $line, 1 ) ] );
                    break;
            }
        }

        return $edits;
    }
}

/**
 * Class used internally by 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:
 * https://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
 *
 * More ideas are taken from:
 * https://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.
 *
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 * @package Text_Diff
 *
 * @access private
 */
class Text_Diff_Engine_native {
    /**
     * @param $from_lines
     * @param $to_lines
     *
     * @return array
     */

    public function diff( $from_lines, $to_lines ) {
        $n_from = count( $from_lines );
        $n_to   = count( $to_lines );

        $this->xchanged = $this->ychanged = [];
        $this->xv       = $this->yv = [];
        $this->xind     = $this->yind = [];

        unset( $this->seq, $this->in_seq, $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 = [];
        $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 = [];
            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 = [];
            while ( $xi < $n_from && $this->xchanged[ $xi ] ) {
                $delete[] = $from_lines[ $xi ++ ];
            }

            $add = [];
            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.
     *
     * @param $xoff
     * @param $xlim
     * @param $yoff
     * @param $ylim
     * @param $nchunks
     *
     * @return array
     */
    public 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 ) = [ $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 = [];
        $ymids[0]     = [];

        $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 ];
                foreach ( $matches as $y ) {
                    if ( empty( $this->in_seq[ $y ] ) ) {
                        $k = $this->_lcsPos( $y );
                        assert( $k > 0 );
                        $ymids[ $k ] = $ymids[ $k - 1 ];
                        break;
                    }
                }
                // TODO @gigamaster replace each (deprecated) with foreach
                // while ( list( $junk, $y ) = each( $matches ) ) {
                    foreach($matches as $junk => $y) {
                    if ( $y > $this->seq[ $k - 1 ] ) {
                        // assert($y < $this->seq[$k]); // GIJ Patched
                        /* 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 ];
                    }
                }
            }
        }

        $seps[] = $flip ? [ $yoff, $xoff ] : [ $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 ? [ $y1, $x1 ] : [ $x1, $y1 ];
        }
        $seps[] = $flip ? [ $ylim, $xlim ] : [ $xlim, $ylim ];

        return [ $this->lcs, $seps ];
    }

    /**
     * @param $ypos
     *
     * @return int
     */

    public function _lcsPos( $ypos ) {
        $end = $this->lcs;
        if ( 0 == $end || $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.
     *
     * @param $xoff
     * @param $xlim
     * @param $yoff
     * @param $ylim
     */
    public 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 ( 0 == $lcs ) {
            /* 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).
     *
     * @param $lines
     * @param $changed
     * @param $other_changed
     */
    public 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] );
            }
        }
    }
}

/**
 * @package Text_Diff
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 *
 * @access private
 */
class Text_Diff_Op {

    public $orig;
    public $final;

    public function reverse() {
        trigger_error( 'Abstract method', E_USER_ERROR );
    }

    /**
     * @return int|void
     */

    public function norig() {
        return $this->orig ? count( $this->orig ) : 0;
    }

    /**
     * @return int|void
     */

    public function nfinal() {
        return $this->final ? count( $this->final ) : 0;
    }
}

/**
 * @package Text_Diff
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 *
 * @access private
 */
class Text_Diff_Op_copy extends Text_Diff_Op {
    /**
     * Text_Diff_Op_copy constructor.
     *
     * @param      $orig
     * @param bool $final
     */

    public function __construct( $orig, $final = false ) {
        if ( ! is_array( $final ) ) {
            $final = $orig;
        }
        $this->orig  = $orig;
        $this->final = $final;
    }

    /**
     * @return \Text_Diff_Op_copy
     */

    public function &reverse() {
        return $reverse = new self( $this->final, $this->orig );
    }
}

/**
 * @package Text_Diff
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 *
 * @access private
 */
class Text_Diff_Op_delete extends Text_Diff_Op {
    /**
     * Text_Diff_Op_delete constructor.
     *
     * @param $lines
     */

    public function __construct( $lines ) {
        $this->orig  = $lines;
        $this->final = false;
    }

    /**
     * @return \Text_Diff_Op_add
     */

    public function &reverse() {
        return $reverse = new Text_Diff_Op_add( $this->orig );
    }
}

/**
 * @package Text_Diff
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 *
 * @access private
 */
class Text_Diff_Op_add extends Text_Diff_Op {
    /**
     * Text_Diff_Op_add constructor.
     *
     * @param $lines
     */

    public function __construct( $lines ) {
        $this->final = $lines;
        $this->orig  = false;
    }

    /**
     * @return \Text_Diff_Op_delete
     */

    public function &reverse() {
        return $reverse = new Text_Diff_Op_delete( $this->final );
    }
}

/**
 * @package Text_Diff
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 *
 * @access private
 */
class Text_Diff_Op_change extends Text_Diff_Op {
    /**
     * Text_Diff_Op_change constructor.
     *
     * @param $orig
     * @param $final
     */

    public function __construct( $orig, $final ) {
        $this->orig  = $orig;
        $this->final = $final;
    }

    /**
     * @return \Text_Diff_Op_change
     */

    public function &reverse() {
        return $reverse = new self( $this->final, $this->orig );
    }
}