Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!spool.mu.edu!snorkelwacker.mit.edu!bloom-beacon!eru!kth.se!cyklop.nada.kth.se!news
From: d88-jwa@byse.nada.kth.se (Jon W{tte)
Newsgroups: comp.compression
Subject: Re: Self Extracting Files
Message-ID: <D88-JWA.91Jun15125054@byse.nada.kth.se>
Date: 15 Jun 91 10:50:58 GMT
References: <309pollarda@physc1.byu.edu>
Sender: news@nada.kth.se (Mr News)
Organization: Royal Institute of Technology, Stockholm, Sweden
Lines: 49
In-reply-to: pollarda@physc1.byu.edu's message of 15 Jun 91 03:53:59 GMT

In article <309pollarda@physc1.byu.edu> pollarda@physc1.byu.edu writes:

   combined somehow.  But how exactly does it work?

   What tells the computer to stop loading in the file as machine code
   and handle the rest as data?

It doesn't. Everything is loaded as code, but the flow in the program
never reached the addresses where the data is. Look at it like a small
program like:

char stuffed_data [ ] = { 0 , 1 , .... } ;

main ()
{
	while ( more_data ) {
		unstuff ( stuffed_data ) ;
	}
}

   type foo.exe

   The Software
   (c) 19xx The Software Co.

   C:>

Just add the text to the beginning with an end-of-file in there.
Maybe some magic numbers still need to be there, but they can be
erased by backspaces... I'm not so very at home with MS-DOS any
longer.



Now, on the mac, this info is in the "vers" resource and comes up
when you "get info" on the icon - and a self-extrancter would have
the code in the usual place (CODE resources) and the data in the
data fork - so you could open it transparently with the original
program as well, which doesn't need to look at the resource fork.
A file system to die for ! :-)

All of this has little to do with comp.compression, except maybe
that archive writers need to be aware that not all file systems
are flat...

--
						Jon W{tte
						h+@nada.kth.se
						- Speed !