[jira] Reopened: (LUCENE-2216) OpenBitSet#hashCode() may return false for identical sets.

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[jira] Reopened: (LUCENE-2216) OpenBitSet#hashCode() may return false for identical sets.

Tim Allison (Jira)

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

Robert Muir reopened LUCENE-2216:
---------------------------------


reopening for possible 2.9.4/3.0.3 backport.


> 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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