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gzip -l 4GB limit

From: Tim Retout
Subject: gzip -l 4GB limit
Date: Thu, 04 Feb 2010 12:59:54 +0000


[I'm not subscribed to bug-gzip, so please CC me.]

I've been trying to find the uncompressed size of gzip files without
decompressing them (to implement a progress bar in some code I'm
writing).  The ISIZE field works, but has two problems:

      * It's modulo 2^32 bits, so for > 4GB the size is wrong.  (See the
        output of gzip -l for instance.)
      * It's stored at the very end of the file, and it would seem more
        convenient to be able to find the original size from the start
        of the file.

There's the ability to add "extra fields" to gzip headers - would it be
appropriate to standardize on an optional extra field that, if present,
can provide the original size of the file without the 2^32 limit of

Then a patch could be written to store this information if we know the
uncompressed size before compressing.

This issue seems to have come up every so often on the bug-gzip mailing
list over the last few years, but no one has fixed it so far (that I
know of).


Tim Retout
Software Developer

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