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https://issues.apache.org/jira/browse/HADOOP-11221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14185346#comment-14185346
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Colin Patrick McCabe commented on HADOOP-11221:
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Thanks, Jinghui. +1
Can you add a comment to the code stating that numEntries must be a power of 2
for this hashing code to work?
> 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,
> HADOOP-11221.v2.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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