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https://issues.apache.org/jira/browse/CASSANDRA-15232?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16891664#comment-16891664
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Benjamin Lerer commented on CASSANDRA-15232:
--------------------------------------------

Regarding,

{quote}  it’s not clear why 128bit was chosen. {quote}

and

{quote} Particularly for multiplication and addition, it’s very unclear why we 
truncate,{quote}

I can add some clarity. It is some mistakes from my part. :-(


> Arithmetic operators over decimal truncate results
> --------------------------------------------------
>
>                 Key: CASSANDRA-15232
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15232
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: CQL/Semantics
>            Reporter: Benedict
>            Assignee: Liudmila Kornilova
>            Priority: Normal
>              Labels: pull-request-available
>             Fix For: 4.0
>
>          Time Spent: 1h 10m
>  Remaining Estimate: 0h
>
> The decimal operators hard-code a 128 bit precision for their computations.  
> Probably a precision needs to be configured or decided somehow, but it’s not 
> clear why 128bit was chosen.  Particularly for multiplication and addition, 
> it’s very unclear why we truncate, which is different to our behaviour for 
> e.g. sum() aggregates.  Probably for division we should also ensure that we 
> do not reduce the precision of the two operands.  A minimum of decimal128 
> seems reasonable, but a maximum does not.



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