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From "Uwe Schindler (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LUCENE-3449) Fix FixedBitSet.nextSetBit/prevSetBit to support the common usage pattern in every programming book
Date Thu, 22 Sep 2011 14:50:26 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-3449?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Uwe Schindler updated LUCENE-3449:
----------------------------------

    Attachment: LUCENE-3449.patch

Patch also fixing the ugly test code.

> Fix FixedBitSet.nextSetBit/prevSetBit to support the common usage pattern in every programming
book
> ---------------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-3449
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3449
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: core/other
>    Affects Versions: 3.4, 4.0
>            Reporter: Uwe Schindler
>            Priority: Minor
>         Attachments: LUCENE-3449.patch
>
>
> The usage pattern for nextSetBit/prevSetBit is the following:
> {code:java}
> for(int i=bs.nextSetBit(0); i>=0; i=bs.nextSetBit(i+1)) {
>  // operate on index i here
> }
> {code}
> The problem is that the i+1 at the end can be bs.length(), but the code in nextSetBit
does not allow this (same applies to prevSetBit(0)). The above usage pattern is in every programming
book, so it should really be supported. The check has to be done in all cases (with the current
impl in the calling code).
> If the check is done inside xxxSetBit() it can also be optimized to be only called seldom
and not all the time, like in the ugly looking replacement, thats currently needed:
> {code:java}
> for(int i=bs.nextSetBit(0); i>=0; i=(i<bs.length()-1) ? bs.nextSetBit(i+1) : -1)
{
>  // operate on index i here
> }
> {code}
> We should change this and allow out-of bounds indexes for those two methods (they already
do some checks in that direction). Enforcing this with an assert is unuseable on the client
side.
> The test code for FixedBitSet also uses this, horrible. Please support the common usage
pattern for BitSets.

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