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https://issues.apache.org/jira/browse/LUCENE-2736?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13034618#comment-13034618
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Doron Cohen commented on LUCENE-2736:
-------------------------------------
Shai, with the modified text the NOTE on "implementations freedom to not
advance beyond in some situations" becomes strange... I think that the original
text stress the fact the "real intended" behavior is to do advance beyond
current, just that for performance reasons the decision whether to advance
beyond in some situations is left for implementation decision, and so, if
caller provides a target which is not greater than current, it should be aware
of this possibility.
So I think it is perhaps better to either not modify this at all, or at most,
to add "(see NOTE below)" just after "beyond":
{noformat}
- * Advances to the first beyond the current whose document number is greater
+ * Advances to the first beyond (see NOTE below) the current whose document
number is greater
{noformat}
This would prevent the confusion I think?
> Wrong implementation of DocIdSetIterator.advance
> -------------------------------------------------
>
> Key: LUCENE-2736
> URL: https://issues.apache.org/jira/browse/LUCENE-2736
> Project: Lucene - Java
> Issue Type: Bug
> Components: core/search
> Affects Versions: 3.2, 4.0
> Reporter: Hardy Ferentschik
> Assignee: Shai Erera
> Attachments: LUCENE-2736.patch
>
>
> Implementations of {{DocIdSetIterator}} behave differently when advanced is
> called. Taking the following test for {{OpenBitSet}}, {{DocIdBitSet}} and
> {{SortedVIntList}} only {{SortedVIntList}} passes the test:
> {code:title=org.apache.lucene.search.TestDocIdSet.java|borderStyle=solid}
> ...
> public void testAdvanceWithOpenBitSet() throws IOException {
> DocIdSet idSet = new OpenBitSet( new long[] { 1121 }, 1 ); //
> bits 0, 5, 6, 10
> assertAdvance( idSet );
> }
> public void testAdvanceDocIdBitSet() throws IOException {
> BitSet bitSet = new BitSet();
> bitSet.set( 0 );
> bitSet.set( 5 );
> bitSet.set( 6 );
> bitSet.set( 10 );
> DocIdSet idSet = new DocIdBitSet(bitSet);
> assertAdvance( idSet );
> }
> public void testAdvanceWithSortedVIntList() throws IOException {
> DocIdSet idSet = new SortedVIntList( 0, 5, 6, 10 );
> assertAdvance( idSet );
> }
> private void assertAdvance(DocIdSet idSet) throws IOException {
> DocIdSetIterator iter = idSet.iterator();
> int docId = iter.nextDoc();
> assertEquals( "First doc id should be 0", 0, docId );
> docId = iter.nextDoc();
> assertEquals( "Second doc id should be 5", 5, docId );
> docId = iter.advance( 5 );
> assertEquals( "Advancing iterator should return the next doc
> id", 6, docId );
> }
> {code}
> The javadoc for {{advance}} says:
> {quote}
> Advances to the first *beyond* the current whose document number is greater
> than or equal to _target_.
> {quote}
> This seems to indicate that {{SortedVIntList}} behaves correctly, whereas the
> other two don't.
> Just looking at the {{DocIdBitSet}} implementation advance is implemented as:
> {code}
> bitSet.nextSetBit(target);
> {code}
> where the docs of {{nextSetBit}} say:
> {quote}
> Returns the index of the first bit that is set to true that occurs *on or
> after* the specified starting index
> {quote}
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