gzip & gunzip not always returning original data

From: <emanuele.lombardi_at_mantegna.casaccia.enea.it>
Date: Thu, 18 Jan 2001 15:44:19 +0100 (CET)

        ES40 4 EV6 cpus running at 500 Mhz
        T64 v5.1 2nd patch
        /usr/bin/gzip -V
                gzip 1.2.4 (18 Aug 93)
                Compilation options:
                DIRENT UTIME STDC_HEADERS HAVE_UNISTD_H

Dear friends,
a user of mine is having trouble gzipping & gunzipping his huge data.
It happens that when a given gzipped file is ungizipped the resulting
data is different from the original.
I have to say that the original file is 624672000 ascii chars and that,
according to Murphy law, the wrong results are given only some times,
not always.

I made the foollowing loop run all nigth

loop:
        gzip < testdata > testdata.gzip
        gunzip < testdata.gzip > testdata.gzip.ungizzipped
        diff testdata testdata.gzip.ungizzipped
        goto loop

and this morning I watched out at the resluts.
Of the 117 executed loops diff has found differences 5 times.

The differences are in few characters each time (not more than 20
different lines reported by each faulty diff). So I see that
statistically the fault rate is almost 0 (20 / 624672000),
nevertheless it is a problem for my user who does'nt trust anymore his
gzipped data.

File systems is Advfs v. 4 and it doesn't send any warning nor error.

Do you have any suggestion ??

Thank you very much from Italy,
Emanuele

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$$$ Emanuele Lombardi
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Received on Thu Jan 18 2001 - 14:45:34 NZDT

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