includes/diff/DairikiDiff.php

   1 <?php
   2 /**
   3  * A PHP diff engine for phpwiki. (Taken from phpwiki-1.3.3)
   4  *
   5  * Copyright © 2000, 2001 Geoffrey T. Dairiki <dairiki@dairiki.org>
   6  * You may copy this code freely under the conditions of the GPL.
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License along
  19  * with this program; if not, write to the Free Software Foundation, Inc.,
  20  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  21  * http://www.gnu.org/copyleft/gpl.html
  22  *
  23  * @file
  24  * @ingroup DifferenceEngine
  25  * @defgroup DifferenceEngine DifferenceEngine
  26  */
  27
  28 /**
  29  * @todo document
  30  * @private
  31  * @ingroup DifferenceEngine
  32  */
  33 abstract class DiffOp {
  34
  35         /**
  36          * @var string
  37          */
  38         public $type;
  39
  40         /**
  41          * @var string[]
  42          */
  43         public $orig;
  44
  45         /**
  46          * @var string[]
  47          */
  48         public $closing;
  49
  50         /**
  51          * @return string
  52          */
  53         public function getType() {
  54                 return $this->type;
  55         }
  56
  57         /**
  58          * @return string[]
  59          */
  60         public function getOrig() {
  61                 return $this->orig;
  62         }
  63
  64         /**
  65          * @param int $i
  66          * @return string|null
  67          */
  68         public function getClosing( $i = null ) {
  69                 if ( $i === null ) {
  70                         return $this->closing;
  71                 }
  72                 if ( array_key_exists( $i, $this->closing ) ) {
  73                         return $this->closing[$i];
  74                 }
  75                 return null;
  76         }
  77
  78         abstract public function reverse();
  79
  80         /**
  81          * @return int
  82          */
  83         public function norig() {
  84                 return $this->orig ? count( $this->orig ) : 0;
  85         }
  86
  87         /**
  88          * @return int
  89          */
  90         public function nclosing() {
  91                 return $this->closing ? count( $this->closing ) : 0;
  92         }
  93 }
  94
  95 /**
  96  * @todo document
  97  * @private
  98  * @ingroup DifferenceEngine
  99  */
 100 class DiffOpCopy extends DiffOp {
 101         public $type = 'copy';
 102
 103         public function __construct( $orig, $closing = false ) {
 104                 if ( !is_array( $closing ) ) {
 105                         $closing = $orig;
 106                 }
 107                 $this->orig = $orig;
 108                 $this->closing = $closing;
 109         }
 110
 111         /**
 112          * @return DiffOpCopy
 113          */
 114         public function reverse() {
 115                 return new DiffOpCopy( $this->closing, $this->orig );
 116         }
 117 }
 118
 119 /**
 120  * @todo document
 121  * @private
 122  * @ingroup DifferenceEngine
 123  */
 124 class DiffOpDelete extends DiffOp {
 125         public $type = 'delete';
 126
 127         public function __construct( $lines ) {
 128                 $this->orig = $lines;
 129                 $this->closing = false;
 130         }
 131
 132         /**
 133          * @return DiffOpAdd
 134          */
 135         public function reverse() {
 136                 return new DiffOpAdd( $this->orig );
 137         }
 138 }
 139
 140 /**
 141  * @todo document
 142  * @private
 143  * @ingroup DifferenceEngine
 144  */
 145 class DiffOpAdd extends DiffOp {
 146         public $type = 'add';
 147
 148         public function __construct( $lines ) {
 149                 $this->closing = $lines;
 150                 $this->orig = false;
 151         }
 152
 153         /**
 154          * @return DiffOpDelete
 155          */
 156         public function reverse() {
 157                 return new DiffOpDelete( $this->closing );
 158         }
 159 }
 160
 161 /**
 162  * @todo document
 163  * @private
 164  * @ingroup DifferenceEngine
 165  */
 166 class DiffOpChange extends DiffOp {
 167         public $type = 'change';
 168
 169         public function __construct( $orig, $closing ) {
 170                 $this->orig = $orig;
 171                 $this->closing = $closing;
 172         }
 173
 174         /**
 175          * @return DiffOpChange
 176          */
 177         public function reverse() {
 178                 return new DiffOpChange( $this->closing, $this->orig );
 179         }
 180 }
 181
 182 /**
 183  * Class used internally by Diff to actually compute the diffs.
 184  *
 185  * The algorithm used here is mostly lifted from the perl module
 186  * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
 187  *     http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
 188  *
 189  * More ideas are taken from:
 190  *     http://www.ics.uci.edu/~eppstein/161/960229.html
 191  *
 192  * Some ideas are (and a bit of code) are from from analyze.c, from GNU
 193  * diffutils-2.7, which can be found at:
 194  *     ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
 195  *
 196  * closingly, some ideas (subdivision by NCHUNKS > 2, and some optimizations)
 197  * are my own.
 198  *
 199  * Line length limits for robustness added by Tim Starling, 2005-08-31
 200  * Alternative implementation added by Guy Van den Broeck, 2008-07-30
 201  *
 202  * @author Geoffrey T. Dairiki, Tim Starling, Guy Van den Broeck
 203  * @private
 204  * @ingroup DifferenceEngine
 205  */
 206 class DiffEngine {
 207         const MAX_XREF_LENGTH = 10000;
 208
 209         protected $xchanged, $ychanged;
 210
 211         protected $xv = array(), $yv = array();
 212         protected $xind = array(), $yind = array();
 213
 214         protected $seq = array(), $in_seq = array();
 215
 216         protected $lcs = 0;
 217
 218         /**
 219          * @param string[] $from_lines
 220          * @param string[] $to_lines
 221          *
 222          * @return DiffOp[]
 223          */
 224         public function diff( $from_lines, $to_lines ) {
 225                 wfProfileIn( __METHOD__ );
 226
 227                 // Diff and store locally
 228                 $this->diffLocal( $from_lines, $to_lines );
 229
 230                 // Merge edits when possible
 231                 $this->shiftBoundaries( $from_lines, $this->xchanged, $this->ychanged );
 232                 $this->shiftBoundaries( $to_lines, $this->ychanged, $this->xchanged );
 233
 234                 // Compute the edit operations.
 235                 $n_from = count( $from_lines );
 236                 $n_to = count( $to_lines );
 237
 238                 $edits = array();
 239                 $xi = $yi = 0;
 240                 while ( $xi < $n_from || $yi < $n_to ) {
 241                         assert( '$yi < $n_to || $this->xchanged[$xi]' );
 242                         assert( '$xi < $n_from || $this->ychanged[$yi]' );
 243
 244                         // Skip matching "snake".
 245                         $copy = array();
 246                         while ( $xi < $n_from && $yi < $n_to
 247                                 && !$this->xchanged[$xi] && !$this->ychanged[$yi]
 248                         ) {
 249                                 $copy[] = $from_lines[$xi++];
 250                                 ++$yi;
 251                         }
 252                         if ( $copy ) {
 253                                 $edits[] = new DiffOpCopy( $copy );
 254                         }
 255
 256                         // Find deletes & adds.
 257                         $delete = array();
 258                         while ( $xi < $n_from && $this->xchanged[$xi] ) {
 259                                 $delete[] = $from_lines[$xi++];
 260                         }
 261
 262                         $add = array();
 263                         while ( $yi < $n_to && $this->ychanged[$yi] ) {
 264                                 $add[] = $to_lines[$yi++];
 265                         }
 266
 267                         if ( $delete && $add ) {
 268                                 $edits[] = new DiffOpChange( $delete, $add );
 269                         } elseif ( $delete ) {
 270                                 $edits[] = new DiffOpDelete( $delete );
 271                         } elseif ( $add ) {
 272                                 $edits[] = new DiffOpAdd( $add );
 273                         }
 274                 }
 275                 wfProfileOut( __METHOD__ );
 276
 277                 return $edits;
 278         }
 279
 280         /**
 281          * @param string[] $from_lines
 282          * @param string[] $to_lines
 283          */
 284         private function diffLocal( $from_lines, $to_lines ) {
 285                 global $wgExternalDiffEngine;
 286                 wfProfileIn( __METHOD__ );
 287
 288                 if ( $wgExternalDiffEngine == 'wikidiff3' ) {
 289                         // wikidiff3
 290                         $wikidiff3 = new WikiDiff3();
 291                         $wikidiff3->diff( $from_lines, $to_lines );
 292                         $this->xchanged = $wikidiff3->removed;
 293                         $this->ychanged = $wikidiff3->added;
 294                         unset( $wikidiff3 );
 295                 } else {
 296                         // old diff
 297                         $n_from = count( $from_lines );
 298                         $n_to = count( $to_lines );
 299                         $this->xchanged = $this->ychanged = array();
 300                         $this->xv = $this->yv = array();
 301                         $this->xind = $this->yind = array();
 302                         unset( $this->seq );
 303                         unset( $this->in_seq );
 304                         unset( $this->lcs );
 305
 306                         // Skip leading common lines.
 307                         for ( $skip = 0; $skip < $n_from && $skip < $n_to; $skip++ ) {
 308                                 if ( $from_lines[$skip] !== $to_lines[$skip] ) {
 309                                         break;
 310                                 }
 311                                 $this->xchanged[$skip] = $this->ychanged[$skip] = false;
 312                         }
 313                         // Skip trailing common lines.
 314                         $xi = $n_from;
 315                         $yi = $n_to;
 316                         for ( $endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++ ) {
 317                                 if ( $from_lines[$xi] !== $to_lines[$yi] ) {
 318                                         break;
 319                                 }
 320                                 $this->xchanged[$xi] = $this->ychanged[$yi] = false;
 321                         }
 322
 323                         // Ignore lines which do not exist in both files.
 324                         for ( $xi = $skip; $xi < $n_from - $endskip; $xi++ ) {
 325                                 $xhash[$this->lineHash( $from_lines[$xi] )] = 1;
 326                         }
 327
 328                         for ( $yi = $skip; $yi < $n_to - $endskip; $yi++ ) {
 329                                 $line = $to_lines[$yi];
 330                                 if ( ( $this->ychanged[$yi] = empty( $xhash[$this->lineHash( $line )] ) ) ) {
 331                                         continue;
 332                                 }
 333                                 $yhash[$this->lineHash( $line )] = 1;
 334                                 $this->yv[] = $line;
 335                                 $this->yind[] = $yi;
 336                         }
 337                         for ( $xi = $skip; $xi < $n_from - $endskip; $xi++ ) {
 338                                 $line = $from_lines[$xi];
 339                                 if ( ( $this->xchanged[$xi] = empty( $yhash[$this->lineHash( $line )] ) ) ) {
 340                                         continue;
 341                                 }
 342                                 $this->xv[] = $line;
 343                                 $this->xind[] = $xi;
 344                         }
 345
 346                         // Find the LCS.
 347                         $this->compareSeq( 0, count( $this->xv ), 0, count( $this->yv ) );
 348                 }
 349                 wfProfileOut( __METHOD__ );
 350         }
 351
 352         /**
 353          * Returns the whole line if it's small enough, or the MD5 hash otherwise
 354          *
 355          * @param string $line
 356          *
 357          * @return string
 358          */
 359         private function lineHash( $line ) {
 360                 if ( strlen( $line ) > self::MAX_XREF_LENGTH ) {
 361                         return md5( $line );
 362                 } else {
 363                         return $line;
 364                 }
 365         }
 366
 367         /**
 368          * Divide the Largest Common Subsequence (LCS) of the sequences
 369          * [XOFF, XLIM) and [YOFF, YLIM) into NCHUNKS approximately equally
 370          * sized segments.
 371          *
 372          * Returns (LCS, PTS). LCS is the length of the LCS. PTS is an
 373          * array of NCHUNKS+1 (X, Y) indexes giving the diving points between
 374          * sub sequences.  The first sub-sequence is contained in [X0, X1),
 375          * [Y0, Y1), the second in [X1, X2), [Y1, Y2) and so on.  Note
 376          * that (X0, Y0) == (XOFF, YOFF) and
 377          * (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
 378          *
 379          * This function assumes that the first lines of the specified portions
 380          * of the two files do not match, and likewise that the last lines do not
 381          * match.  The caller must trim matching lines from the beginning and end
 382          * of the portions it is going to specify.
 383          *
 384          * @param int $xoff
 385          * @param int $xlim
 386          * @param int $yoff
 387          * @param int $ylim
 388          * @param int $nchunks
 389          *
 390          * @return array List of two elements, integer and array[].
 391          */
 392         private function diag( $xoff, $xlim, $yoff, $ylim, $nchunks ) {
 393                 $flip = false;
 394
 395                 if ( $xlim - $xoff > $ylim - $yoff ) {
 396                         // Things seems faster (I'm not sure I understand why)
 397                         // when the shortest sequence in X.
 398                         $flip = true;
 399                         list( $xoff, $xlim, $yoff, $ylim ) = array( $yoff, $ylim, $xoff, $xlim );
 400                 }
 401
 402                 if ( $flip ) {
 403                         for ( $i = $ylim - 1; $i >= $yoff; $i-- ) {
 404                                 $ymatches[$this->xv[$i]][] = $i;
 405                         }
 406                 } else {
 407                         for ( $i = $ylim - 1; $i >= $yoff; $i-- ) {
 408                                 $ymatches[$this->yv[$i]][] = $i;
 409                         }
 410                 }
 411
 412                 $this->lcs = 0;
 413                 $this->seq[0] = $yoff - 1;
 414                 $this->in_seq = array();
 415                 $ymids[0] = array();
 416
 417                 $numer = $xlim - $xoff + $nchunks - 1;
 418                 $x = $xoff;
 419                 for ( $chunk = 0; $chunk < $nchunks; $chunk++ ) {
 420                         if ( $chunk > 0 ) {
 421                                 for ( $i = 0; $i <= $this->lcs; $i++ ) {
 422                                         $ymids[$i][$chunk - 1] = $this->seq[$i];
 423                                 }
 424                         }
 425
 426                         $x1 = $xoff + (int)( ( $numer + ( $xlim - $xoff ) * $chunk ) / $nchunks );
 427                         for ( ; $x < $x1; $x++ ) {
 428                                 $line = $flip ? $this->yv[$x] : $this->xv[$x];
 429                                 if ( empty( $ymatches[$line] ) ) {
 430                                         continue;
 431                                 }
 432
 433                                 $k = 0;
 434                                 $matches = $ymatches[$line];
 435                                 reset( $matches );
 436                                 while ( list( , $y ) = each( $matches ) ) {
 437                                         if ( empty( $this->in_seq[$y] ) ) {
 438                                                 $k = $this->lcsPos( $y );
 439                                                 assert( '$k > 0' );
 440                                                 $ymids[$k] = $ymids[$k - 1];
 441                                                 break;
 442                                         }
 443                                 }
 444
 445                                 while ( list( , $y ) = each( $matches ) ) {
 446                                         if ( $y > $this->seq[$k - 1] ) {
 447                                                 assert( '$y < $this->seq[$k]' );
 448                                                 // Optimization: this is a common case:
 449                                                 //      next match is just replacing previous match.
 450                                                 $this->in_seq[$this->seq[$k]] = false;
 451                                                 $this->seq[$k] = $y;
 452                                                 $this->in_seq[$y] = 1;
 453                                         } elseif ( empty( $this->in_seq[$y] ) ) {
 454                                                 $k = $this->lcsPos( $y );
 455                                                 assert( '$k > 0' );
 456                                                 $ymids[$k] = $ymids[$k - 1];
 457                                         }
 458                                 }
 459                         }
 460                 }
 461
 462                 $seps[] = $flip ? array( $yoff, $xoff ) : array( $xoff, $yoff );
 463                 $ymid = $ymids[$this->lcs];
 464                 for ( $n = 0; $n < $nchunks - 1; $n++ ) {
 465                         $x1 = $xoff + (int)( ( $numer + ( $xlim - $xoff ) * $n ) / $nchunks );
 466                         $y1 = $ymid[$n] + 1;
 467                         $seps[] = $flip ? array( $y1, $x1 ) : array( $x1, $y1 );
 468                 }
 469                 $seps[] = $flip ? array( $ylim, $xlim ) : array( $xlim, $ylim );
 470
 471                 return array( $this->lcs, $seps );
 472         }
 473
 474         /**
 475          * @param int $ypos
 476          *
 477          * @return int
 478          */
 479         private function lcsPos( $ypos ) {
 480                 $end = $this->lcs;
 481                 if ( $end == 0 || $ypos > $this->seq[$end] ) {
 482                         $this->seq[++$this->lcs] = $ypos;
 483                         $this->in_seq[$ypos] = 1;
 484
 485                         return $this->lcs;
 486                 }
 487
 488                 $beg = 1;
 489                 while ( $beg < $end ) {
 490                         $mid = (int)( ( $beg + $end ) / 2 );
 491                         if ( $ypos > $this->seq[$mid] ) {
 492                                 $beg = $mid + 1;
 493                         } else {
 494                                 $end = $mid;
 495                         }
 496                 }
 497
 498                 assert( '$ypos != $this->seq[$end]' );
 499
 500                 $this->in_seq[$this->seq[$end]] = false;
 501                 $this->seq[$end] = $ypos;
 502                 $this->in_seq[$ypos] = 1;
 503
 504                 return $end;
 505         }
 506
 507         /**
 508          * Find LCS of two sequences.
 509          *
 510          * The results are recorded in the vectors $this->{x,y}changed[], by
 511          * storing a 1 in the element for each line that is an insertion
 512          * or deletion (ie. is not in the LCS).
 513          *
 514          * The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.
 515          *
 516          * Note that XLIM, YLIM are exclusive bounds.
 517          * All line numbers are origin-0 and discarded lines are not counted.
 518          *
 519          * @param int $xoff
 520          * @param int $xlim
 521          * @param int $yoff
 522          * @param int $ylim
 523          */
 524         private function compareSeq( $xoff, $xlim, $yoff, $ylim ) {
 525                 // Slide down the bottom initial diagonal.
 526                 while ( $xoff < $xlim && $yoff < $ylim && $this->xv[$xoff] == $this->yv[$yoff] ) {
 527                         ++$xoff;
 528                         ++$yoff;
 529                 }
 530
 531                 // Slide up the top initial diagonal.
 532                 while ( $xlim > $xoff && $ylim > $yoff
 533                         && $this->xv[$xlim - 1] == $this->yv[$ylim - 1]
 534                 ) {
 535                         --$xlim;
 536                         --$ylim;
 537                 }
 538
 539                 if ( $xoff == $xlim || $yoff == $ylim ) {
 540                         $lcs = 0;
 541                 } else {
 542                         // This is ad hoc but seems to work well.
 543                         // $nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);
 544                         // $nchunks = max(2,min(8,(int)$nchunks));
 545                         $nchunks = min( 7, $xlim - $xoff, $ylim - $yoff ) + 1;
 546                         list( $lcs, $seps ) = $this->diag( $xoff, $xlim, $yoff, $ylim, $nchunks );
 547                 }
 548
 549                 if ( $lcs == 0 ) {
 550                         // X and Y sequences have no common subsequence:
 551                         // mark all changed.
 552                         while ( $yoff < $ylim ) {
 553                                 $this->ychanged[$this->yind[$yoff++]] = 1;
 554                         }
 555                         while ( $xoff < $xlim ) {
 556                                 $this->xchanged[$this->xind[$xoff++]] = 1;
 557                         }
 558                 } else {
 559                         // Use the partitions to split this problem into subproblems.
 560                         reset( $seps );
 561                         $pt1 = $seps[0];
 562                         while ( $pt2 = next( $seps ) ) {
 563                                 $this->compareSeq( $pt1[0], $pt2[0], $pt1[1], $pt2[1] );
 564                                 $pt1 = $pt2;
 565                         }
 566                 }
 567         }
 568
 569         /**
 570          * Adjust inserts/deletes of identical lines to join changes
 571          * as much as possible.
 572          *
 573          * We do something when a run of changed lines include a
 574          * line at one end and has an excluded, identical line at the other.
 575          * We are free to choose which identical line is included.
 576          * `compareseq' usually chooses the one at the beginning,
 577          * but usually it is cleaner to consider the following identical line
 578          * to be the "change".
 579          *
 580          * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
 581          */
 582         private function shiftBoundaries( $lines, &$changed, $other_changed ) {
 583                 wfProfileIn( __METHOD__ );
 584                 $i = 0;
 585                 $j = 0;
 586
 587                 assert( 'count($lines) == count($changed)' );
 588                 $len = count( $lines );
 589                 $other_len = count( $other_changed );
 590
 591                 while ( 1 ) {
 592                         /*
 593                          * Scan forwards to find beginning of another run of changes.
 594                          * Also keep track of the corresponding point in the other file.
 595                          *
 596                          * Throughout this code, $i and $j are adjusted together so that
 597                          * the first $i elements of $changed and the first $j elements
 598                          * of $other_changed both contain the same number of zeros
 599                          * (unchanged lines).
 600                          * Furthermore, $j is always kept so that $j == $other_len or
 601                          * $other_changed[$j] == false.
 602                          */
 603                         while ( $j < $other_len && $other_changed[$j] ) {
 604                                 $j++;
 605                         }
 606
 607                         while ( $i < $len && !$changed[$i] ) {
 608                                 assert( '$j < $other_len && ! $other_changed[$j]' );
 609                                 $i++;
 610                                 $j++;
 611                                 while ( $j < $other_len && $other_changed[$j] ) {
 612                                         $j++;
 613                                 }
 614                         }
 615
 616                         if ( $i == $len ) {
 617                                 break;
 618                         }
 619
 620                         $start = $i;
 621
 622                         // Find the end of this run of changes.
 623                         while ( ++$i < $len && $changed[$i] ) {
 624                                 continue;
 625                         }
 626
 627                         do {
 628                                 /*
 629                                  * Record the length of this run of changes, so that
 630                                  * we can later determine whether the run has grown.
 631                                  */
 632                                 $runlength = $i - $start;
 633
 634                                 /*
 635                                  * Move the changed region back, so long as the
 636                                  * previous unchanged line matches the last changed one.
 637                                  * This merges with previous changed regions.
 638                                  */
 639                                 while ( $start > 0 && $lines[$start - 1] == $lines[$i - 1] ) {
 640                                         $changed[--$start] = 1;
 641                                         $changed[--$i] = false;
 642                                         while ( $start > 0 && $changed[$start - 1] ) {
 643                                                 $start--;
 644                                         }
 645                                         assert( '$j > 0' );
 646                                         while ( $other_changed[--$j] ) {
 647                                                 continue;
 648                                         }
 649                                         assert( '$j >= 0 && !$other_changed[$j]' );
 650                                 }
 651
 652                                 /*
 653                                  * Set CORRESPONDING to the end of the changed run, at the last
 654                                  * point where it corresponds to a changed run in the other file.
 655                                  * CORRESPONDING == LEN means no such point has been found.
 656                                  */
 657                                 $corresponding = $j < $other_len ? $i : $len;
 658
 659                                 /*
 660                                  * Move the changed region forward, so long as the
 661                                  * first changed line matches the following unchanged one.
 662                                  * This merges with following changed regions.
 663                                  * Do this second, so that if there are no merges,
 664                                  * the changed region is moved forward as far as possible.
 665                                  */
 666                                 while ( $i < $len && $lines[$start] == $lines[$i] ) {
 667                                         $changed[$start++] = false;
 668                                         $changed[$i++] = 1;
 669                                         while ( $i < $len && $changed[$i] ) {
 670                                                 $i++;
 671                                         }
 672
 673                                         assert( '$j < $other_len && ! $other_changed[$j]' );
 674                                         $j++;
 675                                         if ( $j < $other_len && $other_changed[$j] ) {
 676                                                 $corresponding = $i;
 677                                                 while ( $j < $other_len && $other_changed[$j] ) {
 678                                                         $j++;
 679                                                 }
 680                                         }
 681                                 }
 682                         } while ( $runlength != $i - $start );
 683
 684                         /*
 685                          * If possible, move the fully-merged run of changes
 686                          * back to a corresponding run in the other file.
 687                          */
 688                         while ( $corresponding < $i ) {
 689                                 $changed[--$start] = 1;
 690                                 $changed[--$i] = 0;
 691                                 assert( '$j > 0' );
 692                                 while ( $other_changed[--$j] ) {
 693                                         continue;
 694                                 }
 695                                 assert( '$j >= 0 && !$other_changed[$j]' );
 696                         }
 697                 }
 698                 wfProfileOut( __METHOD__ );
 699         }
 700 }
 701
 702 /**
 703  * Class representing a 'diff' between two sequences of strings.
 704  * @todo document
 705  * @private
 706  * @ingroup DifferenceEngine
 707  */
 708 class Diff {
 709
 710         /**
 711          * @var DiffOp[]
 712          */
 713         public $edits;
 714
 715         /**
 716          * Constructor.
 717          * Computes diff between sequences of strings.
 718          *
 719          * @param string[] $from_lines An array of strings.
 720          *   Typically these are lines from a file.
 721          * @param string[] $to_lines An array of strings.
 722          */
 723         public function __construct( $from_lines, $to_lines ) {
 724                 $eng = new DiffEngine;
 725                 $this->edits = $eng->diff( $from_lines, $to_lines );
 726         }
 727
 728         /**
 729          * @return DiffOp[]
 730          */
 731         public function getEdits() {
 732                 return $this->edits;
 733         }
 734
 735         /**
 736          * Compute reversed Diff.
 737          *
 738          * SYNOPSIS:
 739          *
 740          *    $diff = new Diff($lines1, $lines2);
 741          *    $rev = $diff->reverse();
 742          *
 743          * @return Object A Diff object representing the inverse of the
 744          *   original diff.
 745          */
 746         public function reverse() {
 747                 $rev = $this;
 748                 $rev->edits = array();
 749                 /** @var DiffOp $edit */
 750                 foreach ( $this->edits as $edit ) {
 751                         $rev->edits[] = $edit->reverse();
 752                 }
 753
 754                 return $rev;
 755         }
 756
 757         /**
 758          * Check for empty diff.
 759          *
 760          * @return bool True if two sequences were identical.
 761          */
 762         public function isEmpty() {
 763                 foreach ( $this->edits as $edit ) {
 764                         if ( $edit->type != 'copy' ) {
 765                                 return false;
 766                         }
 767                 }
 768
 769                 return true;
 770         }
 771
 772         /**
 773          * Compute the length of the Longest Common Subsequence (LCS).
 774          *
 775          * This is mostly for diagnostic purposed.
 776          *
 777          * @return int The length of the LCS.
 778          */
 779         public function lcs() {
 780                 $lcs = 0;
 781                 foreach ( $this->edits as $edit ) {
 782                         if ( $edit->type == 'copy' ) {
 783                                 $lcs += count( $edit->orig );
 784                         }
 785                 }
 786
 787                 return $lcs;
 788         }
 789
 790         /**
 791          * Get the original set of lines.
 792          *
 793          * This reconstructs the $from_lines parameter passed to the
 794          * constructor.
 795          *
 796          * @return string[] The original sequence of strings.
 797          */
 798         public function orig() {
 799                 $lines = array();
 800
 801                 foreach ( $this->edits as $edit ) {
 802                         if ( $edit->orig ) {
 803                                 array_splice( $lines, count( $lines ), 0, $edit->orig );
 804                         }
 805                 }
 806
 807                 return $lines;
 808         }
 809
 810         /**
 811          * Get the closing set of lines.
 812          *
 813          * This reconstructs the $to_lines parameter passed to the
 814          * constructor.
 815          *
 816          * @return string[] The sequence of strings.
 817          */
 818         public function closing() {
 819                 $lines = array();
 820
 821                 foreach ( $this->edits as $edit ) {
 822                         if ( $edit->closing ) {
 823                                 array_splice( $lines, count( $lines ), 0, $edit->closing );
 824                         }
 825                 }
 826
 827                 return $lines;
 828         }
 829 }
 830
 831 /**
 832  * @todo document, bad name.
 833  * @private
 834  * @ingroup DifferenceEngine
 835  */
 836 class MappedDiff extends Diff {
 837         /**
 838          * Constructor.
 839          *
 840          * Computes diff between sequences of strings.
 841          *
 842          * This can be used to compute things like
 843          * case-insensitve diffs, or diffs which ignore
 844          * changes in white-space.
 845          *
 846          * @param string[] $from_lines An array of strings.
 847          *   Typically these are lines from a file.
 848          * @param string[] $to_lines An array of strings.
 849          * @param string[] $mapped_from_lines This array should
 850          *   have the same size number of elements as $from_lines.
 851          *   The elements in $mapped_from_lines and
 852          *   $mapped_to_lines are what is actually compared
 853          *   when computing the diff.
 854          * @param string[] $mapped_to_lines This array should
 855          *   have the same number of elements as $to_lines.
 856          */
 857         public function __construct( $from_lines, $to_lines,
 858                 $mapped_from_lines, $mapped_to_lines ) {
 859                 wfProfileIn( __METHOD__ );
 860
 861                 assert( 'count( $from_lines ) == count( $mapped_from_lines )' );
 862                 assert( 'count( $to_lines ) == count( $mapped_to_lines )' );
 863
 864                 parent::__construct( $mapped_from_lines, $mapped_to_lines );
 865
 866                 $xi = $yi = 0;
 867                 $editCount = count( $this->edits );
 868                 for ( $i = 0; $i < $editCount; $i++ ) {
 869                         $orig = &$this->edits[$i]->orig;
 870                         if ( is_array( $orig ) ) {
 871                                 $orig = array_slice( $from_lines, $xi, count( $orig ) );
 872                                 $xi += count( $orig );
 873                         }
 874
 875                         $closing = &$this->edits[$i]->closing;
 876                         if ( is_array( $closing ) ) {
 877                                 $closing = array_slice( $to_lines, $yi, count( $closing ) );
 878                                 $yi += count( $closing );
 879                         }
 880                 }
 881                 wfProfileOut( __METHOD__ );
 882         }
 883 }
 884
 885 /**
 886  * Additions by Axel Boldt follow, partly taken from diff.php, phpwiki-1.3.3
 887  */
 888
 889 /**
 890  * @todo document
 891  * @private
 892  * @ingroup DifferenceEngine
 893  */
 894 class HWLDFWordAccumulator {
 895         public $insClass = ' class="diffchange diffchange-inline"';
 896         public $delClass = ' class="diffchange diffchange-inline"';
 897
 898         private $lines = array();
 899         private $line = '';
 900         private $group = '';
 901         private $tag = '';
 902
 903         /**
 904          * @param string $new_tag
 905          */
 906         private function flushGroup( $new_tag ) {
 907                 if ( $this->group !== '' ) {
 908                         if ( $this->tag == 'ins' ) {
 909                                 $this->line .= "<ins{$this->insClass}>" .
 910                                         htmlspecialchars( $this->group ) . '</ins>';
 911                         } elseif ( $this->tag == 'del' ) {
 912                                 $this->line .= "<del{$this->delClass}>" .
 913                                         htmlspecialchars( $this->group ) . '</del>';
 914                         } else {
 915                                 $this->line .= htmlspecialchars( $this->group );
 916                         }
 917                 }
 918                 $this->group = '';
 919                 $this->tag = $new_tag;
 920         }
 921
 922         /**
 923          * @param string $new_tag
 924          */
 925         private function flushLine( $new_tag ) {
 926                 $this->flushGroup( $new_tag );
 927                 if ( $this->line != '' ) {
 928                         array_push( $this->lines, $this->line );
 929                 } else {
 930                         # make empty lines visible by inserting an NBSP
 931                         array_push( $this->lines, '&#160;' );
 932                 }
 933                 $this->line = '';
 934         }
 935
 936         /**
 937          * @param string[] $words
 938          * @param string $tag
 939          */
 940         public function addWords( $words, $tag = '' ) {
 941                 if ( $tag != $this->tag ) {
 942                         $this->flushGroup( $tag );
 943                 }
 944
 945                 foreach ( $words as $word ) {
 946                         // new-line should only come as first char of word.
 947                         if ( $word == '' ) {
 948                                 continue;
 949                         }
 950                         if ( $word[0] == "\n" ) {
 951                                 $this->flushLine( $tag );
 952                                 $word = substr( $word, 1 );
 953                         }
 954                         assert( '!strstr( $word, "\n" )' );
 955                         $this->group .= $word;
 956                 }
 957         }
 958
 959         /**
 960          * @return string[]
 961          */
 962         public function getLines() {
 963                 $this->flushLine( '~done' );
 964
 965                 return $this->lines;
 966         }
 967 }
 968
 969 /**
 970  * @todo document
 971  * @private
 972  * @ingroup DifferenceEngine
 973  */
 974 class WordLevelDiff extends MappedDiff {
 975         const MAX_LINE_LENGTH = 10000;
 976
 977         /**
 978          * @param string[] $orig_lines
 979          * @param string[] $closing_lines
 980          */
 981         public function __construct( $orig_lines, $closing_lines ) {
 982                 wfProfileIn( __METHOD__ );
 983
 984                 list( $orig_words, $orig_stripped ) = $this->split( $orig_lines );
 985                 list( $closing_words, $closing_stripped ) = $this->split( $closing_lines );
 986
 987                 parent::__construct( $orig_words, $closing_words,
 988                         $orig_stripped, $closing_stripped );
 989                 wfProfileOut( __METHOD__ );
 990         }
 991
 992         /**
 993          * @param string[] $lines
 994          *
 995          * @return array[]
 996          */
 997         private function split( $lines ) {
 998                 wfProfileIn( __METHOD__ );
 999
1000                 $words = array();
1001                 $stripped = array();
1002                 $first = true;
1003                 foreach ( $lines as $line ) {
1004                         # If the line is too long, just pretend the entire line is one big word
1005                         # This prevents resource exhaustion problems
1006                         if ( $first ) {
1007                                 $first = false;
1008                         } else {
1009                                 $words[] = "\n";
1010                                 $stripped[] = "\n";
1011                         }
1012                         if ( strlen( $line ) > self::MAX_LINE_LENGTH ) {
1013                                 $words[] = $line;
1014                                 $stripped[] = $line;
1015                         } else {
1016                                 $m = array();
1017                                 if ( preg_match_all( '/ ( [^\S\n]+ | [0-9_A-Za-z\x80-\xff]+ | . ) (?: (?!< \n) [^\S\n])? /xs',
1018                                         $line, $m )
1019                                 ) {
1020                                         foreach ( $m[0] as $word ) {
1021                                                 $words[] = $word;
1022                                         }
1023                                         foreach ( $m[1] as $stripped_word ) {
1024                                                 $stripped[] = $stripped_word;
1025                                         }
1026                                 }
1027                         }
1028                 }
1029                 wfProfileOut( __METHOD__ );
1030
1031                 return array( $words, $stripped );
1032         }
1033
1034         /**
1035          * @return string[]
1036          */
1037         public function orig() {
1038                 wfProfileIn( __METHOD__ );
1039                 $orig = new HWLDFWordAccumulator;
1040
1041                 foreach ( $this->edits as $edit ) {
1042                         if ( $edit->type == 'copy' ) {
1043                                 $orig->addWords( $edit->orig );
1044                         } elseif ( $edit->orig ) {
1045                                 $orig->addWords( $edit->orig, 'del' );
1046                         }
1047                 }
1048                 $lines = $orig->getLines();
1049                 wfProfileOut( __METHOD__ );
1050
1051                 return $lines;
1052         }
1053
1054         /**
1055          * @return string[]
1056          */
1057         public function closing() {
1058                 wfProfileIn( __METHOD__ );
1059                 $closing = new HWLDFWordAccumulator;
1060
1061                 foreach ( $this->edits as $edit ) {
1062                         if ( $edit->type == 'copy' ) {
1063                                 $closing->addWords( $edit->closing );
1064                         } elseif ( $edit->closing ) {
1065                                 $closing->addWords( $edit->closing, 'ins' );
1066                         }
1067                 }
1068                 $lines = $closing->getLines();
1069                 wfProfileOut( __METHOD__ );
1070
1071                 return $lines;
1072         }
1073
1074 }