[jira] [Created] (LUCENE-6896) Fix/document various Similarity bugs around extreme norm values

["Robert Muir (JIRA)" <ji...@apache.org>]

Robert Muir created LUCENE-6896:
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             Summary: Fix/document various Similarity bugs around extreme norm values
                 Key: LUCENE-6896
                 URL: https://issues.apache.org/jira/browse/LUCENE-6896
             Project: Lucene - Core
          Issue Type: Bug
            Reporter: Robert Muir
             Fix For: 6.0, 5.4


Spinoff from LUCENE-6818:

[~iorixxx] found problems with every Similarity (except ClassicSimilarity) when trying to test how they behave on every possible norm value, to ensure they are robust for all index-time boosts.

There are several problems:
1. buggy normalization decode that causes the smallest possible norm value (0) to be treated as an infinitely long document. These values are intended to be encoded as non-negative finite values, but going to infinity breaks everything.
2. various problems in the less practical functions that already have documented warnings that they do bad things for extreme values. These impact DFR models D, Be, and P and IB distribution SPL.







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