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https://issues.apache.org/jira/browse/HADOOP-11327?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14279330#comment-14279330
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Jason Lowe commented on HADOOP-11327:
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Thanks for picking this up, Eric!
Patch looks good, but I have one nit on the unit test. Rather than unit
testing not() just for the behavior of the lone bit, I think it would be better
to test the other bits as well to ensure the not() method really behaves as
expected. If there had been a proper not() unit test previously then it would
have caught this error and other types of errors that could occur in an
implementation of not().
> BloomFilter#not() omits the last bit, resulting in an incorrect filter
> ----------------------------------------------------------------------
>
> Key: HADOOP-11327
> URL: https://issues.apache.org/jira/browse/HADOOP-11327
> Project: Hadoop Common
> Issue Type: Bug
> Components: util
> Affects Versions: 2.5.1
> Reporter: Tim Luo
> Assignee: Eric Payne
> Priority: Minor
> Attachments: HADOOP-11327.v1.txt
>
>
> There's an off-by-one error in {{BloomFilter#not()}}:
> {{BloomFilter#not}} calls {{BitSet#flip(0, vectorSize - 1)}}, but according
> to the javadoc for that method, {{toIndex}} is end-_exclusive_:
> {noformat}
> * @param toIndex index after the last bit to flip
> {noformat}
> This means that the last bit in the bit array is not flipped.
> Specifically, this was discovered in the following scenario:
> 1. A new/empty {{BloomFilter}} was created with vectorSize=7.
> 2. Invoke {{bloomFilter.not()}}; now expecting a bloom filter with all 7 bits
> (0 through 6) flipped to 1 and membershipTest(...) to always return true.
> 3. However, membershipTest(...) was found to often not return true, and upon
> inspection, the BitSet only had bits 0 through 5 flipped.
> The fix should be simple: remove the "- 1" from the call to {{BitSet#flip}}.
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