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From "Yonik Seeley (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-3582) NumericUtils.floatToSortableInt does not sort certain NaN ranges correctly.
Date Fri, 18 Nov 2011 22:44:51 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-3582?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13153197#comment-13153197
] 

Yonik Seeley commented on LUCENE-3582:
--------------------------------------

We don't really support NaN as a value in Lucene in general I think.  I know that our sorting
(priority queue) methods don't support NaN, and this is why FunctionQuery has the following
code:

{code}
      // Current Lucene priority queues can't handle NaN and -Infinity, so
      // map to -Float.MAX_VALUE. This conditional handles both -infinity
      // and NaN since comparisons with NaN are always false.
      return score>Float.NEGATIVE_INFINITY ? score : -Float.MAX_VALUE;
{code}
                
> NumericUtils.floatToSortableInt does not sort certain NaN ranges correctly.
> ---------------------------------------------------------------------------
>
>                 Key: LUCENE-3582
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3582
>             Project: Lucene - Java
>          Issue Type: Bug
>            Reporter: Dawid Weiss
>            Assignee: Uwe Schindler
>            Priority: Trivial
>             Fix For: 4.0
>
>         Attachments: LUCENE-3582.patch
>
>
> The current implementation of floatToSortableInt does not account for different NaN ranges
which may result in NaNs sorted before -Infinity and after +Infinity. The default Java ordering
is: all NaNs after Infinity.
> A possible fix is to make all NaNs canonic "quiet NaN" as in:
> {code}
> // Canonicalize NaN ranges. I assume this check will be faster here than 
> // (v == v) == false on the FPU? We don't distinguish between different
> // flavors of NaNs here (see http://en.wikipedia.org/wiki/NaN). I guess
> // in Java this doesn't matter much anyway.
> if ((v & 0x7fffffff) > 0x7f800000) {
>   // Apply the logic below to a canonical "quiet NaN"
>   return 0x7fc00000 ^ 0x80000000;
> }
> {code}
> I don't commit because I don't know how much of the existing stuff relies on this (nobody
should be keeping different NaNs  in their indexes, but who knows...).

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