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https://issues.apache.org/jira/browse/DATAFU-46?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matthew Hayes closed DATAFU-46.
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> Hash UDFs should return zero-padded strings of uniform length even when
> leading bits are zero
> ---------------------------------------------------------------------------------------------
>
> Key: DATAFU-46
> URL: https://issues.apache.org/jira/browse/DATAFU-46
> Project: DataFu
> Issue Type: Bug
> Reporter: Matthew Hayes
> Assignee: Philip (flip) Kromer
> Fix For: 1.3.0
>
> Attachments:
> 0001-Hash-UDFs-return-zero-padded-strings-of-uniform-leng.patch
>
>
> Reported by Philip Kromer here:
> https://github.com/linkedin/datafu/issues/93
> Details reported there by Philip:
> ---------------------
> The Hash UDFs in 'hex' mode currently do not return always the same-length
> string, because BigInteger.toString() omits leading zeros. So amidst a stream
> of 94% strings the same length, 1/16th are shorter by one or more characters,
> 1/256th by two or more, and in the unlikely case that an MD5 hash's value was
> 124 bits of zeros and 4 bits of ones it would return the one-character-long
> string 'f'.
> This is surprising behavior, and a trap for those practicing the frequent
> trick of generating a hash and chopping off just the number of bits you need:
> {code}
> -- returns one-fifteenth, not one-sixteenth, of the input.
> sampled_lines = FILTER(FOREACH lines GENERATE MD5(val) AS digest, val) BY
> (STARTSWITH(digest, 'f'));
> {code}
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