On Wed, Aug 27, 2008 at 7:10 PM, Matthew Toseland
<toad at amphibian.dyndns.org> wrote:
> On Wednesday 27 August 2008 09:41, Daniel Cheng wrote:
>> On Wed, Aug 27, 2008 at 5:12 AM, <toad at freenetproject.org> wrote:
>> > Author: toad
>> > Date: 2008-08-26 21:12:19 +0000 (Tue, 26 Aug 2008)
>> > New Revision: 22181
>> >
>> > Modified:
>> > branches/db4o/freenet/src/freenet/support/CountingBloomFilter.java
>> > Log:
>> > FIX MAJOR BUG IN COUNTING BLOOM FILTER:
>> > / 4 not / 8 * 2.
>> > setBit(1000) was effectively also doing setBit(1008).
>> > PORT TO SALTED HASH STORE BRANCH ASAP!
>>
>> Your bloom filters are outdated.
>>
>> The Bloom filters was designed to work only at size of multiples of 8 .
>> Salted hash store took the alternative approach by enforcing this in r22021.
>
> I don't understand how that would produce this bug. I was already using
> multiples of 8.
>
> If you are trying to set bit number 1000, the location will be (with the old
> code) 1000 / 8 * 2 = 250. The specific block within the byte will be 1000 % 4
> = 0. Now, if you try to set bit number 1004, the location with the old code
> will be 1004 / 8 * 2 = 250, and the block within the byte will again be 0.
>
> Have you tried running the BloomFilterTest I committed against your code, with
> a counting filter vs a non-counting one?
>
Oops. yes, thank you.
