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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1136) HashFunction inadvertently destroys some randomness
Date Tue, 20 Jan 2009 00:42:59 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1136?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12665295#action_12665295
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stack commented on HBASE-1136:
------------------------------

Sure, np.  If you look in the build/test dir.. there is a dump of the test output. Or, "ant
-Dtestcase=TestFilter -Dtest.output=yes test" will run just that test and output to console

> HashFunction inadvertently destroys some randomness
> ---------------------------------------------------
>
>                 Key: HBASE-1136
>                 URL: https://issues.apache.org/jira/browse/HBASE-1136
>             Project: Hadoop HBase
>          Issue Type: Bug
>            Reporter: Jonathan Ellis
>             Fix For: 0.20.0
>
>         Attachments: hash.patch
>
>
> the code
>       for (int i = 0, initval = 0; i < nbHash; i++) {
>         initval = result[i] = Math.abs(hashFunction.hash(b, initval) % maxValue);
>       }
> restricts initval for the next hash to the [0, maxValue) range of the hash indexes returned.
 This is suboptimal, particularly for larger nbHash and smaller maxValue.  Instead, use:
>       for (int i = 0, initval = 0; i < nbHash; i++) {
>         initval = hashFunction.hash(b, initval);
>         result[i] = Math.abs(initval) % maxValue;
>       }

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