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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-5255) Fix for HADOOP-5079 HashFunction inadvertently destroys some randomness
Date Fri, 13 Feb 2009 16:34:59 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-5255?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

stack updated HADOOP-5255:
--------------------------

    Attachment: hadoop-core-hash-2-branch-0.20.patch

Jonathan Ellis patch moved over from HADOOP-5079.  Fixes fact that can return negative value
if hash returned is Integer.MIN_VALUE.  Patch is for branch-0.20

> Fix for HADOOP-5079 HashFunction inadvertently destroys some randomness
> -----------------------------------------------------------------------
>
>                 Key: HADOOP-5255
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5255
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: io
>    Affects Versions: 0.20.0, 0.21.0
>            Reporter: stack
>            Priority: Minor
>             Fix For: 0.20.0, 0.21.0
>
>         Attachments: hadoop-core-hash-2-branch-0.20.patch
>
>
> HADOOP-5079 did this "HashFunction.hash 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. Rather we should first set initval, then restrict the range for
the result assignment."  The patch committed on that issue introduced a new bug: "My first
patch contained a regression: you have to take the remainder before calling Math.abs, since
Math.abs(Integer.MIN_VALUE) == Integer.MIN_VALUE still" (Jonathan Ellis).

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