[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Bug#647522: non-deterministic compression results with gzip -n9
From: |
Cyril Brulebois |
Subject: |
Re: Bug#647522: non-deterministic compression results with gzip -n9 |
Date: |
Mon, 13 Feb 2012 01:49:56 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Paul Eggert <address@hidden> (08/02/2012):
> Thanks very much for the patch. But can someone who's looked into it
> please explain why 'window' needs to be zeroed out? This will save me
> time in reviewing the patch. Thanks.
Welcome. Here's a slightly more detailed analysis. You can find attached
the sample files I used (still from the ppl source package). I managed
to track it down to deflate() (what a surprise!), so I decided to check
the matches. Printing match_length only led me to a single difference,
while printing both match_length and match_start (which according to a
comment is set by longest_match()), I got two differences.
To produce the below-quoted diff, using the attached patch, I did:
| tar xfz ppl.tar.gz
| gzip -9f README CREDITS > match-2
| tar xfz ppl.tar.gz
| gzip -9f CREDITS > match-1
| diff -u match-2 match-1
Of course there's an extra file showing up in the diff, but skipping it,
here's the diff:
| match: 46 @ 19459
| match: 8 @ 15659
| match: 8 @ 15659
| -match: 7 @ 17193
| -match: 6 @ 17193
| +match: 6 @ 19510
| +match: 6 @ 19510
| [ no more matches ]
Interestingly, the size of the CREDITS file is 19579.
Mraw,
KiBi.
0001-Pin-point-dirty-window-bug.patch
Description: Text Data
ppl.tar.gz
Description: Binary data
signature.asc
Description: Digital signature