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Date: Thu, 20 Aug 2009 16:32:15 -0700 (PDT)
From: "Tsz Wo (Nicholas), SZE (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Updated: (HDFS-288) Redundant computation in hashCode()
 implemenation
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     [ https://issues.apache.org/jira/browse/HDFS-288?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Tsz Wo (Nicholas), SZE updated HDFS-288:
----------------------------------------

    Release Note: Removed redundant computations from the hashCode() implementations of Block, GenerationStamp and DirectoryScanner.ScanInfo.
    Hadoop Flags: [Incompatible change]

> Redundant computation in hashCode() implemenation
> -------------------------------------------------
>
>                 Key: HDFS-288
>                 URL: https://issues.apache.org/jira/browse/HDFS-288
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Tsz Wo (Nicholas), SZE
>         Attachments: h288_20090820.patch
>
>
> In some hashCode() implementation (e.g. Block.hashCode()), the formula has the form
> {noformat}
> 37 * 17 + f(x),
> {noformat}
> where f( x ) is some function.  Adding 37*17 to f( x ) shifts the value of f( x ).  It is not effective to do shifting in hash functions.  The computation is redundant.

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