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https://issues.apache.org/jira/browse/LUCENE-4546?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13492464#comment-13492464
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Uwe Schindler edited comment on LUCENE-4546 at 11/7/12 9:25 PM:
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Attached the corrected testcase, which passes.

-BTW: Your SorterTemplate implementation fails with with mergeSort completely- 
:-) _(this was incorrect, mergeSort does not use the pivot methods)_
                
      was (Author: thetaphi):
    Attached the corrected testcase, which passes.

BTW: Your SorterTemplate implementation fails with with mergeSort completely :-)
                  
> SorterTemplate.quicksort incorrect
> ----------------------------------
>
>                 Key: LUCENE-4546
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4546
>             Project: Lucene - Core
>          Issue Type: Bug
>          Components: core/other
>    Affects Versions: 3.6.1, 4.0, 4.1
>            Reporter: Stefan Pohl
>            Assignee: Uwe Schindler
>              Labels: patch
>             Fix For: 3.6.1, 4.0, 4.1
>
>         Attachments: SorterTemplate.java.patch, TestSorterTemplate.java, 
> TestSorterTemplate.java
>
>
> On trying to use the very useful o.a.l.utils.SorterTemplate, I stumbled upon 
> inconsistent sorting behaviour, of course, only a randomized test caught 
> this;)
> Because SorterTemplate.quicksort is used in several places in the code 
> (directly BytesRefList, ArrayUtil, BytesRefHash, CollectionUtil and 
> transitively index and search), I'm a bit puzzled that this either hasn't 
> been caught by another higher-level test or that neither my test nor my 
> understanding of an insufficiency in the code is valid;)
> If the former holds and given that the same code is released in 3.6 and 4.0, 
> this might even be a more critical issue requiring a higher priority than 
> 'major'.
> So, can a second pair of eyes please have a timely look at the attached test 
> and patch?
> Basically the current quicksort implementation seems to assume that luckily 
> always the median is chosen as pivot element by grabbing the mid element, not 
> handling the case where the initially chosen pivot ends up not in the middle. 
> Hope this and the test helps to understand the issue.
> Reproducible, currently failing test and a patch attached.

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