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From "Owen O'Malley (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1385) MD5Hash has a bad hash function
Date Thu, 17 May 2007 22:13:16 GMT

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

Owen O'Malley updated HADOOP-1385:
----------------------------------

    Attachment: 1385.patch

This patch adds a new function MD5Hash.quarterDigest() that gives the user the first 4 bytes
as a int. It replaces the current function with a call to quarterDigest. It adds test cases
for the old halfDigest, the new quarterDigest, and a test of the collision.

> 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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