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Message-ID:	<3F291FEB.7080504@cs.york.ac.uk>
Date:	Thu, 31 Jul 2003 14:55:55 +0100
From:	chris <caj AT cs DOT york DOT ac DOT uk>
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CC:	cygwin AT cygwin DOT com
Subject:	Re: Allowing cygwin setup to patch up old versions
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Max Bowsher wrote:

>chris wrote:
>  
>
>>I tend (like I suspect many other people) to update my cygwin every
>>couple of weeks. As cygwin by default keeps packages it downloads it
>>would make sense to distribute patches to existing files.
>>
>>As a tiny example:
>>
>>emacs-21.2-11.tar.bzip2 : 8MB
>>emacs-21.2-12.tar.bzip2 : 8MB
>>patch: 177K
>>
>>emacs-21.2-11-src.tar.bzip2 : 19MB
>>emacs-21.2-12-src.tar.bzip2 : 19MB
>>patch : 3K (!)
>>    
>>
>
>This sounds like a very useful thing to do.
>Question: What format are the patches? Some kind of binary format, I assume,
>since they will need to be able to reconstruct the archives exactly, so the
>MD5 checks can pass.
>  
>

The patch system I am currently using is my personal conversion of the 
bsdiff package from *BSD. I was intending to submit a cygwinized 
version, but have decided that to be honest the program is not of the 
highest quality, so think a re-write of the program would be useful 
before releasing it on innocent people :) Howev bsdiff does create some 
very small patches, and is specially designed to cope with binaries, and 
the kind of differences you get in binaries, better than normal diff 
(mainly things in a different order, and lots of things shifted in value 
by a similar amount) ( http://www.daemonology.net/bsdiff/ if anyone 
wants to see)

The other major thing is that what I diff is (obviously) the .tar files, 
not the .tar.bz2 files, as even a small change to a file usually totally 
changes a compressed version of it. The only problem I can see this 
causing is that the bzip2 files must be compressed in exactly the same 
way. However I expect that everyone will compress their .bzip2s with the 
default, and best setting. If it turns out these files drift then I may 
be forced to MD5 the .tar files. I would like to keep the changes 
required as small as possible tho.

Chris

>  
>
>Such as it is, documentation is at:
>http://sources.redhat.com/cygwin-apps/setup.html
>
>Please join the cygwin-apps AT cygwin DOT com list. That is where setup development
>discussion happens.
>
>Max.
>
>
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>  
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