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   1  <?php
   2  /**
   3   * $Horde: framework/Text_Diff/Diff/Engine/native.php,v 1.10 2008/01/04 10:27:53 jan Exp $
   4   *
   5   * Class used internally by Text_Diff to actually compute the diffs. This
   6   * class is implemented using native PHP code.
   7   *
   8   * The algorithm used here is mostly lifted from the perl module
   9   * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
  10   * http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
  11   *
  12   * More ideas are taken from: http://www.ics.uci.edu/~eppstein/161/960229.html
  13   *
  14   * Some ideas (and a bit of code) are taken from analyze.c, of GNU
  15   * diffutils-2.7, which can be found at:
  16   * ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
  17   *
  18   * Some ideas (subdivision by NCHUNKS > 2, and some optimizations) are from
  19   * Geoffrey T. Dairiki <dairiki@dairiki.org>. The original PHP version of this
  20   * code was written by him, and is used/adapted with his permission.
  21   *
  22   * Copyright 2004-2008 The Horde Project (http://www.horde.org/)
  23   *
  24   * See the enclosed file COPYING for license information (LGPL). If you did
  25   * not receive this file, see http://opensource.org/licenses/lgpl-license.php.
  26   *
  27   * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
  28   * @package Text_Diff
  29   */
  30  class Text_Diff_Engine_native {
  31  
  32      function diff($from_lines, $to_lines)
  33      {
  34          array_walk($from_lines, array('Text_Diff', 'trimNewlines'));
  35          array_walk($to_lines, array('Text_Diff', 'trimNewlines'));
  36  
  37          $n_from = count($from_lines);
  38          $n_to = count($to_lines);
  39  
  40          $this->xchanged = $this->ychanged = array();
  41          $this->xv = $this->yv = array();
  42          $this->xind = $this->yind = array();
  43          unset($this->seq);
  44          unset($this->in_seq);
  45          unset($this->lcs);
  46  
  47          // Skip leading common lines.
  48          for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) {
  49              if ($from_lines[$skip] !== $to_lines[$skip]) {
  50                  break;
  51              }
  52              $this->xchanged[$skip] = $this->ychanged[$skip] = false;
  53          }
  54  
  55          // Skip trailing common lines.
  56          $xi = $n_from; $yi = $n_to;
  57          for ($endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++) {
  58              if ($from_lines[$xi] !== $to_lines[$yi]) {
  59                  break;
  60              }
  61              $this->xchanged[$xi] = $this->ychanged[$yi] = false;
  62          }
  63  
  64          // Ignore lines which do not exist in both files.
  65          for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
  66              $xhash[$from_lines[$xi]] = 1;
  67          }
  68          for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {
  69              $line = $to_lines[$yi];
  70              if (($this->ychanged[$yi] = empty($xhash[$line]))) {
  71                  continue;
  72              }
  73              $yhash[$line] = 1;
  74              $this->yv[] = $line;
  75              $this->yind[] = $yi;
  76          }
  77          for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
  78              $line = $from_lines[$xi];
  79              if (($this->xchanged[$xi] = empty($yhash[$line]))) {
  80                  continue;
  81              }
  82              $this->xv[] = $line;
  83              $this->xind[] = $xi;
  84          }
  85  
  86          // Find the LCS.
  87          $this->_compareseq(0, count($this->xv), 0, count($this->yv));
  88  
  89          // Merge edits when possible.
  90          $this->_shiftBoundaries($from_lines, $this->xchanged, $this->ychanged);
  91          $this->_shiftBoundaries($to_lines, $this->ychanged, $this->xchanged);
  92  
  93          // Compute the edit operations.
  94          $edits = array();
  95          $xi = $yi = 0;
  96          while ($xi < $n_from || $yi < $n_to) {
  97              assert($yi < $n_to || $this->xchanged[$xi]);
  98              assert($xi < $n_from || $this->ychanged[$yi]);
  99  
 100              // Skip matching "snake".
 101              $copy = array();
 102              while ($xi < $n_from && $yi < $n_to
 103                     && !$this->xchanged[$xi] && !$this->ychanged[$yi]) {
 104                  $copy[] = $from_lines[$xi++];
 105                  ++$yi;
 106              }
 107              if ($copy) {
 108                  $edits[] = &new Text_Diff_Op_copy($copy);
 109              }
 110  
 111              // Find deletes & adds.
 112              $delete = array();
 113              while ($xi < $n_from && $this->xchanged[$xi]) {
 114                  $delete[] = $from_lines[$xi++];
 115              }
 116  
 117              $add = array();
 118              while ($yi < $n_to && $this->ychanged[$yi]) {
 119                  $add[] = $to_lines[$yi++];
 120              }
 121  
 122              if ($delete && $add) {
 123                  $edits[] = &new Text_Diff_Op_change($delete, $add);
 124              } elseif ($delete) {
 125                  $edits[] = &new Text_Diff_Op_delete($delete);
 126              } elseif ($add) {
 127                  $edits[] = &new Text_Diff_Op_add($add);
 128              }
 129          }
 130  
 131          return $edits;
 132      }
 133  
 134      /**
 135       * Divides the Largest Common Subsequence (LCS) of the sequences (XOFF,
 136       * XLIM) and (YOFF, YLIM) into NCHUNKS approximately equally sized
 137       * segments.
 138       *
 139       * Returns (LCS, PTS).  LCS is the length of the LCS. PTS is an array of
 140       * NCHUNKS+1 (X, Y) indexes giving the diving points between sub
 141       * sequences.  The first sub-sequence is contained in (X0, X1), (Y0, Y1),
 142       * the second in (X1, X2), (Y1, Y2) and so on.  Note that (X0, Y0) ==
 143       * (XOFF, YOFF) and (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
 144       *
 145       * This function assumes that the first lines of the specified portions of
 146       * the two files do not match, and likewise that the last lines do not
 147       * match.  The caller must trim matching lines from the beginning and end
 148       * of the portions it is going to specify.
 149       */
 150      function _diag ($xoff, $xlim, $yoff, $ylim, $nchunks)
 151      {
 152          $flip = false;
 153  
 154          if ($xlim - $xoff > $ylim - $yoff) {
 155              /* Things seems faster (I'm not sure I understand why) when the
 156               * shortest sequence is in X. */
 157              $flip = true;
 158              list ($xoff, $xlim, $yoff, $ylim)
 159                  = array($yoff, $ylim, $xoff, $xlim);
 160          }
 161  
 162          if ($flip) {
 163              for ($i = $ylim - 1; $i >= $yoff; $i--) {
 164                  $ymatches[$this->xv[$i]][] = $i;
 165              }
 166          } else {
 167              for ($i = $ylim - 1; $i >= $yoff; $i--) {
 168                  $ymatches[$this->yv[$i]][] = $i;
 169              }
 170          }
 171  
 172          $this->lcs = 0;
 173          $this->seq[0]= $yoff - 1;
 174          $this->in_seq = array();
 175          $ymids[0] = array();
 176  
 177          $numer = $xlim - $xoff + $nchunks - 1;
 178          $x = $xoff;
 179          for ($chunk = 0; $chunk < $nchunks; $chunk++) {
 180              if ($chunk > 0) {
 181                  for ($i = 0; $i <= $this->lcs; $i++) {
 182                      $ymids[$i][$chunk - 1] = $this->seq[$i];
 183                  }
 184              }
 185  
 186              $x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $chunk) / $nchunks);
 187              for (; $x < $x1; $x++) {
 188                  $line = $flip ? $this->yv[$x] : $this->xv[$x];
 189                  if (empty($ymatches[$line])) {
 190                      continue;
 191                  }
 192                  $matches = $ymatches[$line];
 193                  reset($matches);
 194                  while (list(, $y) = each($matches)) {
 195                      if (empty($this->in_seq[$y])) {
 196                          $k = $this->_lcsPos($y);
 197                          assert($k > 0);
 198                          $ymids[$k] = $ymids[$k - 1];
 199                          break;
 200                      }
 201                  }
 202                  while (list(, $y) = each($matches)) {
 203                      if ($y > $this->seq[$k - 1]) {
 204                          assert($y <= $this->seq[$k]);
 205                          /* Optimization: this is a common case: next match is
 206                           * just replacing previous match. */
 207                          $this->in_seq[$this->seq[$k]] = false;
 208                          $this->seq[$k] = $y;
 209                          $this->in_seq[$y] = 1;
 210                      } elseif (empty($this->in_seq[$y])) {
 211                          $k = $this->_lcsPos($y);
 212                          assert($k > 0);
 213                          $ymids[$k] = $ymids[$k - 1];
 214                      }
 215                  }
 216              }
 217          }
 218  
 219          $seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);
 220          $ymid = $ymids[$this->lcs];
 221          for ($n = 0; $n < $nchunks - 1; $n++) {
 222              $x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $n) / $nchunks);
 223              $y1 = $ymid[$n] + 1;
 224              $seps[] = $flip ? array($y1, $x1) : array($x1, $y1);
 225          }
 226          $seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);
 227  
 228          return array($this->lcs, $seps);
 229      }
 230  
 231      function _lcsPos($ypos)
 232      {
 233          $end = $this->lcs;
 234          if ($end == 0 || $ypos > $this->seq[$end]) {
 235              $this->seq[++$this->lcs] = $ypos;
 236              $this->in_seq[$ypos] = 1;
 237              return $this->lcs;
 238          }
 239  
 240          $beg = 1;
 241          while ($beg < $end) {
 242              $mid = (int)(($beg + $end) / 2);
 243              if ($ypos > $this->seq[$mid]) {
 244                  $beg = $mid + 1;
 245              } else {
 246                  $end = $mid;
 247              }
 248          }
 249  
 250          assert($ypos != $this->seq[$end]);
 251  
 252          $this->in_seq[$this->seq[$end]] = false;
 253          $this->seq[$end] = $ypos;
 254          $this->in_seq[$ypos] = 1;
 255          return $end;
 256      }
 257  
 258      /**
 259       * Finds LCS of two sequences.
 260       *
 261       * The results are recorded in the vectors $this->{x,y}changed[], by
 262       * storing a 1 in the element for each line that is an insertion or
 263       * deletion (ie. is not in the LCS).
 264       *
 265       * The subsequence of file 0 is (XOFF, XLIM) and likewise for file 1.
 266       *
 267       * Note that XLIM, YLIM are exclusive bounds.  All line numbers are
 268       * origin-0 and discarded lines are not counted.
 269       */
 270      function _compareseq ($xoff, $xlim, $yoff, $ylim)
 271      {
 272          /* Slide down the bottom initial diagonal. */
 273          while ($xoff < $xlim && $yoff < $ylim
 274                 && $this->xv[$xoff] == $this->yv[$yoff]) {
 275              ++$xoff;
 276              ++$yoff;
 277          }
 278  
 279          /* Slide up the top initial diagonal. */
 280          while ($xlim > $xoff && $ylim > $yoff
 281                 && $this->xv[$xlim - 1] == $this->yv[$ylim - 1]) {
 282              --$xlim;
 283              --$ylim;
 284          }
 285  
 286          if ($xoff == $xlim || $yoff == $ylim) {
 287              $lcs = 0;
 288          } else {
 289              /* This is ad hoc but seems to work well.  $nchunks =
 290               * sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5); $nchunks =
 291               * max(2,min(8,(int)$nchunks)); */
 292              $nchunks = min(7, $xlim - $xoff, $ylim - $yoff) + 1;
 293              list($lcs, $seps)
 294                  = $this->_diag($xoff, $xlim, $yoff, $ylim, $nchunks);
 295          }
 296  
 297          if ($lcs == 0) {
 298              /* X and Y sequences have no common subsequence: mark all
 299               * changed. */
 300              while ($yoff < $ylim) {
 301                  $this->ychanged[$this->yind[$yoff++]] = 1;
 302              }
 303              while ($xoff < $xlim) {
 304                  $this->xchanged[$this->xind[$xoff++]] = 1;
 305              }
 306          } else {
 307              /* Use the partitions to split this problem into subproblems. */
 308              reset($seps);
 309              $pt1 = $seps[0];
 310              while ($pt2 = next($seps)) {
 311                  $this->_compareseq ($pt1[0], $pt2[0], $pt1[1], $pt2[1]);
 312                  $pt1 = $pt2;
 313              }
 314          }
 315      }
 316  
 317      /**
 318       * Adjusts inserts/deletes of identical lines to join changes as much as
 319       * possible.
 320       *
 321       * We do something when a run of changed lines include a line at one end
 322       * and has an excluded, identical line at the other.  We are free to
 323       * choose which identical line is included.  `compareseq' usually chooses
 324       * the one at the beginning, but usually it is cleaner to consider the
 325       * following identical line to be the "change".
 326       *
 327       * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
 328       */
 329      function _shiftBoundaries($lines, &$changed, $other_changed)
 330      {
 331          $i = 0;
 332          $j = 0;
 333  
 334          assert('count($lines) == count($changed)');
 335          $len = count($lines);
 336          $other_len = count($other_changed);
 337  
 338          while (1) {
 339              /* Scan forward to find the beginning of another run of
 340               * changes. Also keep track of the corresponding point in the
 341               * other file.
 342               *
 343               * Throughout this code, $i and $j are adjusted together so that
 344               * the first $i elements of $changed and the first $j elements of
 345               * $other_changed both contain the same number of zeros (unchanged
 346               * lines).
 347               *
 348               * Furthermore, $j is always kept so that $j == $other_len or
 349               * $other_changed[$j] == false. */
 350              while ($j < $other_len && $other_changed[$j]) {
 351                  $j++;
 352              }
 353  
 354              while ($i < $len && ! $changed[$i]) {
 355                  assert('$j < $other_len && ! $other_changed[$j]');
 356                  $i++; $j++;
 357                  while ($j < $other_len && $other_changed[$j]) {
 358                      $j++;
 359                  }
 360              }
 361  
 362              if ($i == $len) {
 363                  break;
 364              }
 365  
 366              $start = $i;
 367  
 368              /* Find the end of this run of changes. */
 369              while (++$i < $len && $changed[$i]) {
 370                  continue;
 371              }
 372  
 373              do {
 374                  /* Record the length of this run of changes, so that we can
 375                   * later determine whether the run has grown. */
 376                  $runlength = $i - $start;
 377  
 378                  /* Move the changed region back, so long as the previous
 379                   * unchanged line matches the last changed one.  This merges
 380                   * with previous changed regions. */
 381                  while ($start > 0 && $lines[$start - 1] == $lines[$i - 1]) {
 382                      $changed[--$start] = 1;
 383                      $changed[--$i] = false;
 384                      while ($start > 0 && $changed[$start - 1]) {
 385                          $start--;
 386                      }
 387                      assert('$j > 0');
 388                      while ($other_changed[--$j]) {
 389                          continue;
 390                      }
 391                      assert('$j >= 0 && !$other_changed[$j]');
 392                  }
 393  
 394                  /* Set CORRESPONDING to the end of the changed run, at the
 395                   * last point where it corresponds to a changed run in the
 396                   * other file. CORRESPONDING == LEN means no such point has
 397                   * been found. */
 398                  $corresponding = $j < $other_len ? $i : $len;
 399  
 400                  /* Move the changed region forward, so long as the first
 401                   * changed line matches the following unchanged one.  This
 402                   * merges with following changed regions.  Do this second, so
 403                   * that if there are no merges, the changed region is moved
 404                   * forward as far as possible. */
 405                  while ($i < $len && $lines[$start] == $lines[$i]) {
 406                      $changed[$start++] = false;
 407                      $changed[$i++] = 1;
 408                      while ($i < $len && $changed[$i]) {
 409                          $i++;
 410                      }
 411  
 412                      assert('$j < $other_len && ! $other_changed[$j]');
 413                      $j++;
 414                      if ($j < $other_len && $other_changed[$j]) {
 415                          $corresponding = $i;
 416                          while ($j < $other_len && $other_changed[$j]) {
 417                              $j++;
 418                          }
 419                      }
 420                  }
 421              } while ($runlength != $i - $start);
 422  
 423              /* If possible, move the fully-merged run of changes back to a
 424               * corresponding run in the other file. */
 425              while ($corresponding < $i) {
 426                  $changed[--$start] = 1;
 427                  $changed[--$i] = 0;
 428                  assert('$j > 0');
 429                  while ($other_changed[--$j]) {
 430                      continue;
 431                  }
 432                  assert('$j >= 0 && !$other_changed[$j]');
 433              }
 434          }
 435      }
 436  
 437  }