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Posted to common-issues@hadoop.apache.org by "Tim Luo (JIRA)" <ji...@apache.org> on 2015/01/13 23:19:35 UTC
[jira] [Updated] (HADOOP-11327) BloomFilter#not() omits the last
bit, resulting in an incorrect filter
[ https://issues.apache.org/jira/browse/HADOOP-11327?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Tim Luo updated HADOOP-11327:
-----------------------------
Assignee: Eric Payne (was: Tim Luo)
> 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
>
> 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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