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From "Robert Muir (JIRA)" <>
Subject [jira] Commented: (LUCENE-1813) Add option to ReverseStringFilter to mark reversed tokens
Date Sun, 16 Aug 2009 23:52:14 GMT


Robert Muir commented on LUCENE-1813:

another issue, besides the fact they are deprecated, is that tag characters are outside of
the BMP. 

Currently, the reverse filter does not properly reverse characters outside of the BMP [it
does not recognize them as one character], 
This means characters such as tag characters will be 'reversed' into trail surrogate followed
by lead surrogate (two unpaired surrogates).
But we cannot fix the above, as lucene wildcard support does not recognize codepoints >
FFFF as one 'character' either.

If we are gonna pick a character other than U+0001, it needs to be inside the BMP.

> Add option to ReverseStringFilter to mark reversed tokens
> ---------------------------------------------------------
>                 Key: LUCENE-1813
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: contrib/analyzers
>    Affects Versions: 2.9
>            Reporter: Andrzej Bialecki 
>            Assignee: Robert Muir
>             Fix For: 2.9
>         Attachments: reverseMark-2.patch, reverseMark.patch
> This patch implements additional functionality in the filter to "mark" reversed tokens
with a special marker character (Unicode 0001). This is useful when indexing both straight
and reversed tokens (e.g. to implement efficient leading wildcards search).

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