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From "Uwe Schindler (JIRA)" <j...@apache.org>
Subject [jira] Resolved: (LUCENE-2216) OpenBitSet#hashCode() may return false for identical sets.
Date Tue, 23 Nov 2010 13:22:57 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-2216?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Uwe Schindler resolved LUCENE-2216.
-----------------------------------

    Resolution: Fixed

Backported 3.0 revision: 1038096
Backported 2.9 revision: 1038098

> OpenBitSet#hashCode() may return false for identical sets.
> ----------------------------------------------------------
>
>                 Key: LUCENE-2216
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2216
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Other
>    Affects Versions: 2.9, 2.9.1, 3.0
>            Reporter: Dawid Weiss
>            Priority: Minor
>             Fix For: 2.9.4, 3.0.3
>
>         Attachments: LUCENE-2216.patch, openbitset.patch
>
>
> OpenBitSet uses an internal buffer of long variables to store set bits and an additional
'wlen' index that points 
> to the highest used component inside {@link #bits} buffer.
> Unlike in JDK, the wlen field is not continuously maintained (on clearing bits, for example).
This leads to a situation when wlen may point
> far beyond the last set bit. 
> The hashCode implementation iterates over all long components of the bits buffer, rotating
the hash even for empty components. This is against the contract of hashCode-equals. The following
test case illustrates this:
> {code}
> // initialize two bitsets with different capacity (bits length).
> BitSet bs1 = new BitSet(200);
> BitSet bs2 = new BitSet(64);
> // set the same bit.
> bs1.set(3);
> bs2.set(3);
>         
> // equals returns true (passes).
> assertEquals(bs1, bs2);
> // hashCode returns false (against contract).
> assertEquals(bs1.hashCode(), bs2.hashCode());
> {code}
> Fix and test case attached.

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