native.php

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<?php
/**
 * $Horde: framework/Text_Diff/Diff/Engine/native.php,v 1.10 2008/01/04 10:27:53 jan Exp $
 *
 * Class used internally by Text_Diff to actually compute the diffs. This
 * class is implemented using native PHP code.
 *
 * The algorithm used here is mostly lifted from the perl module
 * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
 * http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
 *
 * More ideas are taken from: http://www.ics.uci.edu/~eppstein/161/960229.html
 *
 * Some ideas (and a bit of code) are taken from analyze.c, of GNU
 * diffutils-2.7, which can be found at:
 * ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
 *
 * Some ideas (subdivision by NCHUNKS > 2, and some optimizations) are from
 * Geoffrey T. Dairiki <[e-mail]>. The original PHP version of this
 * code was written by him, and is used/adapted with his permission.
 *
 * Copyright 2004-2008 The Horde Project (http://www.horde.org/)
 *
 * See the enclosed file COPYING for license information (LGPL). If you did
 * not receive this file, see http://opensource.org/licenses/lgpl-license.php.
 *
 * @author  Geoffrey T. Dairiki <[e-mail]>
 * @package Text_Diff
 */
class Text_Diff_Engine_native {

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

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

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

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

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

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

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

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

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

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

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

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

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

        return $edits;
    }

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

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

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

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

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

            $x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $chunk) / $nchunks);
            for (; $x < $x1; $x++) {
                $line = $flip ? $this->yv[$x] : $this->xv[$x];
                if (empty($ymatches[$line])) {
                    continue;
                }
                $matches = $ymatches[$line];
                reset($matches);
                while (list(, $y) = each($matches)) {
                    if (empty($this->in_seq[$y])) {
                        $k = $this->_lcsPos($y);
                        assert($k > 0);
                        $ymids[$k] = $ymids[$k - 1];
                        break;
                    }
                }
                while (list(, $y) = each($matches)) {
                    if ($y > $this->seq[$k - 1]) {
                        assert($y <= $this->seq[$k]);
                        /* Optimization: this is a common case: next match is
                         * just replacing previous match. */
                        $this->in_seq[$this->seq[$k]] = false;
                        $this->seq[$k] = $y;
                        $this->in_seq[$y] = 1;
                    } elseif (empty($this->in_seq[$y])) {
                        $k = $this->_lcsPos($y);
                        assert($k > 0);
                        $ymids[$k] = $ymids[$k - 1];
                    }
                }
            }
        }

        $seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);