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From "Robert Chansler (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HDFS-288) Redundant computation in hashCode() implemenation
Date Fri, 09 Oct 2009 18:55:31 GMT

     [ https://issues.apache.org/jira/browse/HDFS-288?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Robert Chansler updated HDFS-288:
---------------------------------

    Release Note:   (was: Removed redundant computations from the hashCode() implementations
of Block, GenerationStamp and DirectoryScanner.ScanInfo.)

Editorial pass over all release notes prior to publication of 0.21.

> 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
>            Assignee: Tsz Wo (Nicholas), SZE
>             Fix For: 0.21.0
>
>         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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