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From "Tim Luo (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-11327) BloomFilter#not() omits the last bit, resulting in an incorrect filter
Date Fri, 21 Nov 2014 22:42:33 GMT
Tim Luo created HADOOP-11327:
--------------------------------

             Summary: 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: Tim Luo
            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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