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From "Eric Payne (JIRA)" <j...@apache.org>
Subject [jira] [Work started] (HADOOP-11327) BloomFilter#not() omits the last bit, resulting in an incorrect filter
Date Tue, 13 Jan 2015 22:50:35 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-11327?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Work on HADOOP-11327 started by Eric Payne.
-------------------------------------------
> 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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