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Summery Summery
Finds LCS of two sequences.
Syntax Syntax
Description Description
The results are recorded in the vectors $this->{x,y}changed[], by storing a 1 in the element for each line that is an insertion or deletion (ie. is not in the LCS).
The subsequence of file 0 is (XOFF, XLIM) and likewise for file 1.
Note that XLIM, YLIM are exclusive bounds. All line numbers are origin-0 and discarded lines are not counted.
Source Source
File: wp-includes/Text/Diff/Engine/native.php
function _compareseq ($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, $nchunks);
}
if ($lcs == 0) {
/* 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;
}
}
}