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https://issues.apache.org/jira/browse/LUCENE-3179?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13054578#comment-13054578
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Uwe Schindler commented on LUCENE-3179:
---------------------------------------
The check for negative indexes must be done to make the following loop work
(which is standard to iterate backwards from "startBit" on all bits):
{code:java}
for (int i = bs.prevSetBit(startBit); i >= 0; i = bs.prevSetBit(i-1)) {
// operate on index i here
}
{code}
This would fail with AIOOBE when i=0 on the last iteration (happens if 0th bit
is set), because bs.prevSetBit(i-1) has negative parameter. The exit condition
is checked later, so -1 must be allowed.
> OpenBitSet.prevSetBit()
> -----------------------
>
> Key: LUCENE-3179
> URL: https://issues.apache.org/jira/browse/LUCENE-3179
> Project: Lucene - Java
> Issue Type: Improvement
> Reporter: Paul Elschot
> Priority: Minor
> Fix For: 3.3, 4.0
>
> Attachments: LUCENE-3179-fix.patch, LUCENE-3179.patch,
> LUCENE-3179.patch, LUCENE-3179.patch, TestBitUtil.java, TestOpenBitSet.patch
>
>
> Find a previous set bit in an OpenBitSet.
> Useful for parent testing in nested document query execution LUCENE-2454 .
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