PHP Diff Algorithm

[PaulButler]

I wrote a simple diff algorithm in PHP. The functions are described in the comments; basically the "diff" function works directly on an array and the htmlDiff function is a wrapper that takes two normal strings and returns HTML markup representing the difference.

I assume that the "largest common substring" algorithm is the one I used, but I did not have any code or description to base it on so I had to figure most of it out myself. Considering diff algorithms are fairly useful and fun but challenging to code, I am surprised that there is so little information on them on the web.

php:

<?php /*         Paul's Simple Diff Algorithm v 0.1         (C) Paul Butler 2007 <http://www.paulbutler.org/>         May be used and distributed under the zlib/libpng license.                 This code is intended for learning purposes; it was written with short         code taking priority over performance. It could be used in a practical         application, but there are a few ways it could be optimized.                 Given two arrays, the function diff will return an array of the changes.         I won't describe the format of the array, but it will be obvious         if you use print_r() on the result of a diff on some test data.                 htmlDiff is a wrapper for the diff command, it takes two strings and         returns the differences in HTML. The tags used are <ins> and <del>,         which can easily be styled with CSS.  */ function diff($old, $new){         foreach($old as $oindex => $ovalue){                 $nkeys = array_keys($new, $ovalue);                 foreach($nkeys as $nindex){                         $matrix[$oindex][$nindex] = isset($matrix[$oindex - 1][$nindex - 1]) ?                                 $matrix[$oindex - 1][$nindex - 1] + 1 : 1;                         if($matrix[$oindex][$nindex] > $maxlen){                                 $maxlen = $matrix[$oindex][$nindex];                                 $omax = $oindex + 1 - $maxlen;                                 $nmax = $nindex + 1 - $maxlen;                         }                 }                }         if($maxlen == 0) return array(array('d'=>$old, 'i'=>$new));         return array_merge(                 diff(array_slice($old, 0, $omax), array_slice($new, 0, $nmax)),                 array_slice($new, $nmax, $maxlen),                 diff(array_slice($old, $omax + $maxlen), array_slice($new, $nmax + $maxlen))); } function htmlDiff($old, $new){         $diff = diff(explode(' ', $old), explode(' ', $new));         foreach($diff as $k){                 if(is_array($k))                         $ret .= (!empty($k['d'])?"<del>".implode(' ',$k['d'])."</del> ":'').                                 (!empty($k['i'])?"<ins>".implode(' ',$k['i'])."</ins> ":'');                 else $ret .= $k . ' ';         }         return $ret; } ?>

[Somsakjohn]

I was very impressed that I had a message on it. Size and promised to use it.