Tomoko Uchida created LUCENE-10610:
--------------------------------------
Summary: RunAutomaton#hashCode() can easily cause hash collision
for different Automatons
Key: LUCENE-10610
URL: https://issues.apache.org/jira/browse/LUCENE-10610
Project: Lucene - Core
Issue Type: Bug
Reporter: Tomoko Uchida
Current RunAutomaton#hashCode() is:
{code:java}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + alphabetSize;
result = prime * result + points.length;
result = prime * result + size;
return result;
}
{code}
Since it does not take account of the contents of the {{points}} array, this
returns the same value for different automatons when their alphabet size and
state size are the same.
For example, this test code passes.
{code:java}
public void testHashCode() throws IOException {
PrefixQuery q1 = new PrefixQuery(new Term("field", "aba"));
PrefixQuery q2 = new PrefixQuery(new Term("field", "fee"));
assert q1.compiled.runAutomaton.hashCode() ==
q2.compiled.runAutomaton.hashCode();
}
{code}
I suspect this is a bug?
Note that I think it's not a serious one; all callers of this {{hashCode()}}
take account of additional information when calculating their own hash value,
it seems there is no substantial impact on higher-level APIs.
--
This message was sent by Atlassian Jira
(v8.20.7#820007)
---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscr...@lucene.apache.org
For additional commands, e-mail: issues-h...@lucene.apache.org
