CRC32 == 0?

Sorry, I'm not a mathematician and need the answer to a fairly simple
question: is it possible for the CRC32 of a file to be 0 when the file
is of nonzero length? It's fairly obvious that it's 0 when there is no
data but I'd like to be able to infer the reverse, that a CRC of 0 means
there was no data in the file. I expect the answer is "No, 0 is as
likely as any other value for a given sequence of bytes" but am hoping
to be proved wrong.

Thanks,
RM

Rex Mottram <rexm@not.here> writes:

> Sorry, I'm not a mathematician and need the answer to a fairly simple
> question: is it possible for the CRC32 of a file to be 0 when the file
> is of nonzero length? It's fairly obvious that it's 0 when there is no
> data but I'd like to be able to infer the reverse, that a CRC of 0
> means there was no data in the file. I expect the answer is "No, 0 is
> as likely as any other value for a given sequence of bytes" but am
> hoping to be proved wrong.

No, 0 is as likely as anything.  Calculate the CRC of some data,
append the CRC to the end, and include this in the CRC calculation.
You should get a final CRC of zero.  Or something like that.

--
Måns Rullgård
mans@mansr.com