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Date: Mon, 19 Jan 2009 22:38:59 -0800 (PST)
From: "stack (JIRA)" <jira@apache.org>
To: hbase-dev@hadoop.apache.org
Subject: [jira] Resolved: (HBASE-1136) HashFunction inadvertently destroys
 some randomness
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     [ https://issues.apache.org/jira/browse/HBASE-1136?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

stack resolved HBASE-1136.
--------------------------

    Resolution: Fixed

Committed (again).  Thanks for the fixup Jonathan.

There is no unit test up in Hadoop.

> 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, hbase-testfilter.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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