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From "Owen O'Malley (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1385) MD5Hash has a bad hash function
Date Fri, 18 May 2007 21:10:16 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12497041
] 

Owen O'Malley commented on HADOOP-1385:
---------------------------------------

I think it wouldn't be a good test case to make sure the collision happens if the fifth bytes
are different. If at some point we xor all of the words together, that would be ok and should
cause regression failures.

> MD5Hash has a bad hash function
> -------------------------------
>
>                 Key: HADOOP-1385
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1385
>             Project: Hadoop
>          Issue Type: Bug
>          Components: io
>    Affects Versions: 0.12.3
>            Reporter: Owen O'Malley
>         Assigned To: Owen O'Malley
>             Fix For: 0.13.0
>
>         Attachments: 1385.patch
>
>
> The MD5Hash class has a really bad hash function, that will cause most most md5s to hash
to 0xFFFFFFxx leaving only the low order byte as meaningful. The problem comes from the automatic
sign extension when promoting from byte to int.

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