Now, you said "compressed files" and you might not have meant
pictures, but note that L-Z style compressed files don't really have
much in the way of headers. If the headers were a problem, you'd
expect longer files to bury any deviation in the noise, but it
doesn't. The longer the files I test the more certainly non-random
they are.
I stand by my statements.
Greg.
Hello, Greg!
I did not say anything about pictures. I only said that it's not that hard
to find a compression algorithm or a source of randomness or a simple PRNG
that will pass all kinds of randomness tests. You said it's hard, I said it
wasn't. Maybe you want to try testing something packed with WinRK or Durilca
for example. You could probably even test the whole files packed with
them...
Although I totally agree with you that JPEG or ZIP (Deflate) or LZ
compressed data could only pass randomness tests if the data was random to
begin with. But come on, such weak ancient algorithms hardly qualify as
randomness benchmarks. Modern decent compression algorithms like those used
in Stuffit or Allume reduce JPEGs by about 25% or so (losslessly). No wonder
your tests show a bias!
On the other hand, maybe you have an amazing brilliant randomness test there
that fails all the compressed files and makes diehard look like a baby's
rattle... If that is the case, do share! ;-)
Ruptor
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