I've written a patch which adds two new functions to PHP4, wordwrap & wordwrap_byte which break a string buffer at word boundaries at a given maximum line length using either a string or single-char delimiter respectively. The byte function is MUCH faster since it needs no memory copying (which is why I wrote it as a separate function).
I've written this specifically for PHP-based email programs such as IMP which have major performance problems due to the nessesity of doing this in PHP code which is still very slow at this particular problem. I'm sure it could be useful for other purposes as well.
patch can be found on the php-dev mailing list June 20th, search subject: wordwrap
or at:
http://kavik.ccs.yorku.ca/misc/php-4.0.0-wordwrap-patch

I know there are a few developers hoping this will make it into main. If there's anything I can do to help the process or make the patch more acceptable please let me know.
Thanks
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Chris Russel
russel@yorku.ca