bloom filter: use unsigned quantities for signed math
bloom filter: use unsigned quantities for signed math

We are using signed quantities to be compatible with the code java uses.
However, the current code will eventually overflow.

To avoid that, let's cast the quantities to unsigned, and then back to signed

Signed-off-by: Glauber Costa <f8b79557d19b40666ebe336545a0b6178af65685@cloudius-systems.com>

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