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:

More ideas are taken from:

Some ideas (and a bit of code) are taken from analyze.c, of GNU diffutils-2.7, which can be found at:

Some ideas (subdivision by NCHUNKS > 2, and some optimizations) are from Geoffrey T. Dairiki The original PHP version of this code was written by him, and is used/adapted with his permission.

Copyright 2004-2010 The Horde Project (

See the enclosed file COPYING for license information (LGPL). If you did not receive this file, see

author Geoffrey T. Dairiki
package Text_Diff


Finds LCS of two sequences.

_compareseq($xoff, $xlim, $yoff, $ylim) 

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.






Divides the Largest Common Subsequence (LCS) of the sequences (XOFF, XLIM) and (YOFF, YLIM) into NCHUNKS approximately equally sized segments.

_diag($xoff, $xlim, $yoff, $ylim, $nchunks) 

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.











Adjusts inserts/deletes of identical lines to join changes as much as possible.

_shiftBoundaries($lines, $changed, $other_changed) 

We do something when a run of changed lines include a line at one end and has an excluded, identical line at the other. We are free to choose which identical line is included. `compareseq' usually chooses the one at the beginning, but usually it is cleaner to consider the following identical line to be the "change".

This is extracted verbatim from analyze.c (GNU diffutils-2.7).






diff($from_lines, $to_lines)