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Diffstat (limited to 'includes/diff/WikiDiff3.php')
| -rw-r--r-- | includes/diff/WikiDiff3.php | 586 |
1 files changed, 586 insertions, 0 deletions
diff --git a/includes/diff/WikiDiff3.php b/includes/diff/WikiDiff3.php new file mode 100644 index 00000000..8def296d --- /dev/null +++ b/includes/diff/WikiDiff3.php @@ -0,0 +1,586 @@ +<?php +/** + * New version of the difference engine + * + * Copyright © 2008 Guy Van den Broeck <guy@guyvdb.eu> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + * http://www.gnu.org/copyleft/gpl.html + * + * @file + * @ingroup DifferenceEngine + */ + +/** + * This diff implementation is mainly lifted from the LCS algorithm of the Eclipse project which + * in turn is based on Myers' "An O(ND) difference algorithm and its variations" + * (http://citeseer.ist.psu.edu/myers86ond.html) with range compression (see Wu et al.'s + * "An O(NP) Sequence Comparison Algorithm"). + * + * This implementation supports an upper bound on the excution time. + * + * Complexity: O((M + N)D) worst case time, O(M + N + D^2) expected time, O(M + N) space + * + * @author Guy Van den Broeck + * @ingroup DifferenceEngine + */ +class WikiDiff3 { + + // Input variables + private $from; + private $to; + private $m; + private $n; + + private $tooLong; + private $powLimit; + + // State variables + private $maxDifferences; + private $lcsLengthCorrectedForHeuristic = false; + + // Output variables + public $length; + public $removed; + public $added; + public $heuristicUsed; + + function __construct( $tooLong = 2000000, $powLimit = 1.45 ) { + $this->tooLong = $tooLong; + $this->powLimit = $powLimit; + } + + public function diff( /*array*/ $from, /*array*/ $to ) { + // remember initial lengths + $m = sizeof( $from ); + $n = count( $to ); + + $this->heuristicUsed = false; + + // output + $removed = $m > 0 ? array_fill( 0, $m, true ) : array(); + $added = $n > 0 ? array_fill( 0, $n, true ) : array(); + + // reduce the complexity for the next step (intentionally done twice) + // remove common tokens at the start + $i = 0; + while ( $i < $m && $i < $n && $from[$i] === $to[$i] ) { + $removed[$i] = $added[$i] = false; + unset( $from[$i], $to[$i] ); + ++$i; + } + + // remove common tokens at the end + $j = 1; + while ( $i + $j <= $m && $i + $j <= $n && $from[$m - $j] === $to[$n - $j] ) { + $removed[$m - $j] = $added[$n - $j] = false; + unset( $from[$m - $j], $to[$n - $j] ); + ++$j; + } + + $this->from = $newFromIndex = $this->to = $newToIndex = array(); + + // remove tokens not in both sequences + $shared = array(); + foreach ( $from as $key ) { + $shared[$key] = false; + } + + foreach ( $to as $index => &$el ) { + if ( array_key_exists( $el, $shared ) ) { + // keep it + $this->to[] = $el; + $shared[$el] = true; + $newToIndex[] = $index; + } + } + foreach ( $from as $index => &$el ) { + if ( $shared[$el] ) { + // keep it + $this->from[] = $el; + $newFromIndex[] = $index; + } + } + + unset( $shared, $from, $to ); + + $this->m = count( $this->from ); + $this->n = count( $this->to ); + + $this->removed = $this->m > 0 ? array_fill( 0, $this->m, true ) : array(); + $this->added = $this->n > 0 ? array_fill( 0, $this->n, true ) : array(); + + if ( $this->m == 0 || $this->n == 0 ) { + $this->length = 0; + } else { + $this->maxDifferences = ceil( ( $this->m + $this->n ) / 2.0 ); + if ( $this->m * $this->n > $this->tooLong ) { + // limit complexity to D^POW_LIMIT for long sequences + $this->maxDifferences = floor( pow( $this->maxDifferences, $this->powLimit - 1.0 ) ); + wfDebug( "Limiting max number of differences to $this->maxDifferences\n" ); + } + + /* + * The common prefixes and suffixes are always part of some LCS, include + * them now to reduce our search space + */ + $max = min( $this->m, $this->n ); + for ( $forwardBound = 0; $forwardBound < $max + && $this->from[$forwardBound] === $this->to[$forwardBound]; + ++$forwardBound ) { + $this->removed[$forwardBound] = $this->added[$forwardBound] = false; + } + + $backBoundL1 = $this->m - 1; + $backBoundL2 = $this->n - 1; + + while ( $backBoundL1 >= $forwardBound && $backBoundL2 >= $forwardBound + && $this->from[$backBoundL1] === $this->to[$backBoundL2] ) { + $this->removed[$backBoundL1--] = $this->added[$backBoundL2--] = false; + } + + $temp = array_fill( 0, $this->m + $this->n + 1, 0 ); + $V = array( $temp, $temp ); + $snake = array( 0, 0, 0 ); + + $this->length = $forwardBound + $this->m - $backBoundL1 - 1 + + $this->lcs_rec( $forwardBound, $backBoundL1, + $forwardBound, $backBoundL2, $V, $snake ); + } + + $this->m = $m; + $this->n = $n; + + $this->length += $i + $j - 1; + + foreach ( $this->removed as $key => &$removed_elem ) { + if ( !$removed_elem ) { + $removed[$newFromIndex[$key]] = false; + } + } + foreach ( $this->added as $key => &$added_elem ) { + if ( !$added_elem ) { + $added[$newToIndex[$key]] = false; + } + } + $this->removed = $removed; + $this->added = $added; + } + + function diff_range( $from_lines, $to_lines ) { + // Diff and store locally + $this->diff( $from_lines, $to_lines ); + unset( $from_lines, $to_lines ); + + $ranges = array(); + $xi = $yi = 0; + while ( $xi < $this->m || $yi < $this->n ) { + // Matching "snake". + while ( $xi < $this->m && $yi < $this->n + && !$this->removed[$xi] + && !$this->added[$yi] ) { + ++$xi; + ++$yi; + } + // Find deletes & adds. + $xstart = $xi; + while ( $xi < $this->m && $this->removed[$xi] ) { + ++$xi; + } + + $ystart = $yi; + while ( $yi < $this->n && $this->added[$yi] ) { + ++$yi; + } + + if ( $xi > $xstart || $yi > $ystart ) { + $ranges[] = new RangeDifference( $xstart, $xi, + $ystart, $yi ); + } + } + return $ranges; + } + + private function lcs_rec( $bottoml1, $topl1, $bottoml2, $topl2, &$V, &$snake ) { + // check that both sequences are non-empty + if ( $bottoml1 > $topl1 || $bottoml2 > $topl2 ) { + return 0; + } + + $d = $this->find_middle_snake( $bottoml1, $topl1, $bottoml2, + $topl2, $V, $snake ); + + // need to store these so we don't lose them when they're + // overwritten by the recursion + $len = $snake[2]; + $startx = $snake[0]; + $starty = $snake[1]; + + // the middle snake is part of the LCS, store it + for ( $i = 0; $i < $len; ++$i ) { + $this->removed[$startx + $i] = $this->added[$starty + $i] = false; + } + + if ( $d > 1 ) { + return $len + + $this->lcs_rec( $bottoml1, $startx - 1, $bottoml2, + $starty - 1, $V, $snake ) + + $this->lcs_rec( $startx + $len, $topl1, $starty + $len, + $topl2, $V, $snake ); + } else if ( $d == 1 ) { + /* + * In this case the sequences differ by exactly 1 line. We have + * already saved all the lines after the difference in the for loop + * above, now we need to save all the lines before the difference. + */ + $max = min( $startx - $bottoml1, $starty - $bottoml2 ); + for ( $i = 0; $i < $max; ++$i ) { + $this->removed[$bottoml1 + $i] = + $this->added[$bottoml2 + $i] = false; + } + return $max + $len; + } + return $len; + } + + private function find_middle_snake( $bottoml1, $topl1, $bottoml2, $topl2, &$V, &$snake ) { + $from = &$this->from; + $to = &$this->to; + $V0 = &$V[0]; + $V1 = &$V[1]; + $snake0 = &$snake[0]; + $snake1 = &$snake[1]; + $snake2 = &$snake[2]; + $bottoml1_min_1 = $bottoml1 -1; + $bottoml2_min_1 = $bottoml2 -1; + $N = $topl1 - $bottoml1_min_1; + $M = $topl2 - $bottoml2_min_1; + $delta = $N - $M; + $maxabsx = $N + $bottoml1; + $maxabsy = $M + $bottoml2; + $limit = min( $this->maxDifferences, ceil( ( $N + $M ) / 2 ) ); + + // value_to_add_forward: a 0 or 1 that we add to the start + // offset to make it odd/even + if ( ( $M & 1 ) == 1 ) { + $value_to_add_forward = 1; + } else { + $value_to_add_forward = 0; + } + + if ( ( $N & 1 ) == 1 ) { + $value_to_add_backward = 1; + } else { + $value_to_add_backward = 0; + } + + $start_forward = -$M; + $end_forward = $N; + $start_backward = -$N; + $end_backward = $M; + + $limit_min_1 = $limit - 1; + $limit_plus_1 = $limit + 1; + + $V0[$limit_plus_1] = 0; + $V1[$limit_min_1] = $N; + $limit = min( $this->maxDifferences, ceil( ( $N + $M ) / 2 ) ); + + if ( ( $delta & 1 ) == 1 ) { + for ( $d = 0; $d <= $limit; ++$d ) { + $start_diag = max( $value_to_add_forward + $start_forward, -$d ); + $end_diag = min( $end_forward, $d ); + $value_to_add_forward = 1 - $value_to_add_forward; + + // compute forward furthest reaching paths + for ( $k = $start_diag; $k <= $end_diag; $k += 2 ) { + if ( $k == -$d || ( $k < $d + && $V0[$limit_min_1 + $k] < $V0[$limit_plus_1 + $k] ) ) { + $x = $V0[$limit_plus_1 + $k]; + } else { + $x = $V0[$limit_min_1 + $k] + 1; + } + + $absx = $snake0 = $x + $bottoml1; + $absy = $snake1 = $x - $k + $bottoml2; + + while ( $absx < $maxabsx && $absy < $maxabsy && $from[$absx] === $to[$absy] ) { + ++$absx; + ++$absy; + } + $x = $absx -$bottoml1; + + $snake2 = $absx -$snake0; + $V0[$limit + $k] = $x; + if ( $k >= $delta - $d + 1 && $k <= $delta + $d - 1 + && $x >= $V1[$limit + $k - $delta] ) { + return 2 * $d - 1; + } + + // check to see if we can cut down the diagonal range + if ( $x >= $N && $end_forward > $k - 1 ) { + $end_forward = $k - 1; + } else if ( $absy - $bottoml2 >= $M ) { + $start_forward = $k + 1; + $value_to_add_forward = 0; + } + } + + $start_diag = max( $value_to_add_backward + $start_backward, -$d ); + $end_diag = min( $end_backward, $d ); + $value_to_add_backward = 1 - $value_to_add_backward; + + // compute backward furthest reaching paths + for ( $k = $start_diag; $k <= $end_diag; $k += 2 ) { + if ( $k == $d + || ( $k != -$d && $V1[$limit_min_1 + $k] < $V1[$limit_plus_1 + $k] ) ) { + $x = $V1[$limit_min_1 + $k]; + } else { + $x = $V1[$limit_plus_1 + $k] - 1; + } + + $y = $x - $k - $delta; + + $snake2 = 0; + while ( $x > 0 && $y > 0 + && $from[$x + $bottoml1_min_1] === $to[$y + $bottoml2_min_1] ) { + --$x; + --$y; + ++$snake2; + } + $V1[$limit + $k] = $x; + + // check to see if we can cut down our diagonal range + if ( $x <= 0 ) { + $start_backward = $k + 1; + $value_to_add_backward = 0; + } else if ( $y <= 0 && $end_backward > $k - 1 ) { + $end_backward = $k - 1; + } + } + } + } else { + for ( $d = 0; $d <= $limit; ++$d ) { + $start_diag = max( $value_to_add_forward + $start_forward, -$d ); + $end_diag = min( $end_forward, $d ); + $value_to_add_forward = 1 - $value_to_add_forward; + + // compute forward furthest reaching paths + for ( $k = $start_diag; $k <= $end_diag; $k += 2 ) { + if ( $k == -$d + || ( $k < $d && $V0[$limit_min_1 + $k] < $V0[$limit_plus_1 + $k] ) ) { + $x = $V0[$limit_plus_1 + $k]; + } else { + $x = $V0[$limit_min_1 + $k] + 1; + } + + $absx = $snake0 = $x + $bottoml1; + $absy = $snake1 = $x - $k + $bottoml2; + + while ( $absx < $maxabsx && $absy < $maxabsy && $from[$absx] === $to[$absy] ) { + ++$absx; + ++$absy; + } + $x = $absx -$bottoml1; + $snake2 = $absx -$snake0; + $V0[$limit + $k] = $x; + + // check to see if we can cut down the diagonal range + if ( $x >= $N && $end_forward > $k - 1 ) { + $end_forward = $k - 1; + } else if ( $absy -$bottoml2 >= $M ) { + $start_forward = $k + 1; + $value_to_add_forward = 0; + } + } + + $start_diag = max( $value_to_add_backward + $start_backward, -$d ); + $end_diag = min( $end_backward, $d ); + $value_to_add_backward = 1 - $value_to_add_backward; + + // compute backward furthest reaching paths + for ( $k = $start_diag; $k <= $end_diag; $k += 2 ) { + if ( $k == $d + || ( $k != -$d && $V1[$limit_min_1 + $k] < $V1[$limit_plus_1 + $k] ) ) { + $x = $V1[$limit_min_1 + $k]; + } else { + $x = $V1[$limit_plus_1 + $k] - 1; + } + + $y = $x - $k - $delta; + + $snake2 = 0; + while ( $x > 0 && $y > 0 + && $from[$x + $bottoml1_min_1] === $to[$y + $bottoml2_min_1] ) { + --$x; + --$y; + ++$snake2; + } + $V1[$limit + $k] = $x; + + if ( $k >= -$delta - $d && $k <= $d - $delta + && $x <= $V0[$limit + $k + $delta] ) { + $snake0 = $bottoml1 + $x; + $snake1 = $bottoml2 + $y; + return 2 * $d; + } + + // check to see if we can cut down our diagonal range + if ( $x <= 0 ) { + $start_backward = $k + 1; + $value_to_add_backward = 0; + } else if ( $y <= 0 && $end_backward > $k - 1 ) { + $end_backward = $k - 1; + } + } + } + } + /* + * computing the true LCS is too expensive, instead find the diagonal + * with the most progress and pretend a midle snake of length 0 occurs + * there. + */ + + $most_progress = self::findMostProgress( $M, $N, $limit, $V ); + + $snake0 = $bottoml1 + $most_progress[0]; + $snake1 = $bottoml2 + $most_progress[1]; + $snake2 = 0; + wfDebug( "Computing the LCS is too expensive. Using a heuristic.\n" ); + $this->heuristicUsed = true; + return 5; /* + * HACK: since we didn't really finish the LCS computation + * we don't really know the length of the SES. We don't do + * anything with the result anyway, unless it's <=1. We know + * for a fact SES > 1 so 5 is as good a number as any to + * return here + */ + } + + private static function findMostProgress( $M, $N, $limit, $V ) { + $delta = $N - $M; + + if ( ( $M & 1 ) == ( $limit & 1 ) ) { + $forward_start_diag = max( -$M, -$limit ); + } else { + $forward_start_diag = max( 1 - $M, -$limit ); + } + + $forward_end_diag = min( $N, $limit ); + + if ( ( $N & 1 ) == ( $limit & 1 ) ) { + $backward_start_diag = max( -$N, -$limit ); + } else { + $backward_start_diag = max( 1 - $N, -$limit ); + } + + $backward_end_diag = -min( $M, $limit ); + + $temp = array( 0, 0, 0 ); + + + $max_progress = array_fill( 0, ceil( max( $forward_end_diag - $forward_start_diag, + $backward_end_diag - $backward_start_diag ) / 2 ), $temp ); + $num_progress = 0; // the 1st entry is current, it is initialized + // with 0s + + // first search the forward diagonals + for ( $k = $forward_start_diag; $k <= $forward_end_diag; $k += 2 ) { + $x = $V[0][$limit + $k]; + $y = $x - $k; + if ( $x > $N || $y > $M ) { + continue; + } + + $progress = $x + $y; + if ( $progress > $max_progress[0][2] ) { + $num_progress = 0; + $max_progress[0][0] = $x; + $max_progress[0][1] = $y; + $max_progress[0][2] = $progress; + } else if ( $progress == $max_progress[0][2] ) { + ++$num_progress; + $max_progress[$num_progress][0] = $x; + $max_progress[$num_progress][1] = $y; + $max_progress[$num_progress][2] = $progress; + } + } + + $max_progress_forward = true; // initially the maximum + // progress is in the forward + // direction + + // now search the backward diagonals + for ( $k = $backward_start_diag; $k <= $backward_end_diag; $k += 2 ) { + $x = $V[1][$limit + $k]; + $y = $x - $k - $delta; + if ( $x < 0 || $y < 0 ) { + continue; + } + + $progress = $N - $x + $M - $y; + if ( $progress > $max_progress[0][2] ) { + $num_progress = 0; + $max_progress_forward = false; + $max_progress[0][0] = $x; + $max_progress[0][1] = $y; + $max_progress[0][2] = $progress; + } else if ( $progress == $max_progress[0][2] && !$max_progress_forward ) { + ++$num_progress; + $max_progress[$num_progress][0] = $x; + $max_progress[$num_progress][1] = $y; + $max_progress[$num_progress][2] = $progress; + } + } + + // return the middle diagonal with maximal progress. + return $max_progress[floor( $num_progress / 2 )]; + } + + public function getLcsLength() { + if ( $this->heuristicUsed && !$this->lcsLengthCorrectedForHeuristic ) { + $this->lcsLengthCorrectedForHeuristic = true; + $this->length = $this->m -array_sum( $this->added ); + } + return $this->length; + } + +} + +/** + * Alternative representation of a set of changes, by the index + * ranges that are changed. + * + * @ingroup DifferenceEngine + */ +class RangeDifference { + + public $leftstart; + public $leftend; + public $leftlength; + + public $rightstart; + public $rightend; + public $rightlength; + + function __construct( $leftstart, $leftend, $rightstart, $rightend ) { + $this->leftstart = $leftstart; + $this->leftend = $leftend; + $this->leftlength = $leftend - $leftstart; + $this->rightstart = $rightstart; + $this->rightend = $rightend; + $this->rightlength = $rightend - $rightstart; + } +} |