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https://issues.apache.org/jira/browse/HADOOP-11221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14182327#comment-14182327
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Tsz Wo Nicholas Sze commented on HADOOP-11221:
----------------------------------------------
The capacity of an IdentityHashStore and buffer.length (=4*capacity) are powers
of 2. Therefore, we may use & to calculate positive mod, i.e.
{code}
final int hash = System.identityHashCode(k);
final int numEntries = buffer.length >> 1;
final int index = hash & (numEntries - 1);
{code}
> JAVA specification for hashcode does not enforce it to be non-negative, but
> IdentityHashStore assumes System.identityHashCode() is non-negative
> -----------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-11221
> URL: https://issues.apache.org/jira/browse/HADOOP-11221
> Project: Hadoop Common
> Issue Type: Bug
> Components: util
> Affects Versions: 2.4.1
> Reporter: Jinghui Wang
> Assignee: Jinghui Wang
> Attachments: HADOOP-11221.patch, HADOOP-11221.v1.patch
>
>
> The following code snippet shows that IdentityHashStore assumes the hashCode
> is always non-negative.
> {code:borderStyle=solid}
> private void putInternal(Object k, Object v) {
> int hash = System.identityHashCode(k);
> final int numEntries = buffer.length / 2;
> int index = hash % numEntries;
> ...
> }
>
> private int getElementIndex(K k) {
> ...
> final int numEntries = buffer.length / 2;
> int hash = System.identityHashCode(k);
> int index = hash % numEntries;
> int firstIndex = index;
> ...
> }
> {code}
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