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From "Phil Steitz (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MATH-151) MathUtils.round incorrect result
Date Sun, 11 Jun 2006 18:00:31 GMT
    [ http://issues.apache.org/jira/browse/MATH-151?page=comments#action_12415774 ] 

Phil Steitz commented on MATH-151:
----------------------------------

Sorry, messed up the link yet again.  Best to just look at
http://svn.apache.org/viewvc/jakarta/commons/proper/math/trunk/src/java/org/apache/commons/math/util/MathUtils.java?view=log
or use a svn client to examine history. 

I also neglected to mention that part of the reason for the change to the new impl was performance.
  I played with some microbenchmarks to confirm this some time ago, seeing about 5x-8x improvement
in the direct impl.  It might be a good idea to do this testing rigorously.  

If we could characterize the inputs somehow that have "bad" IEEE754 representations, perhaps
we could use the BigDecimal-based impl just for them.   I don't see any reliable way to do
that, though.

> MathUtils.round incorrect result
> --------------------------------
>
>          Key: MATH-151
>          URL: http://issues.apache.org/jira/browse/MATH-151
>      Project: Commons Math
>         Type: Bug

>     Versions: 1.1 Final
>  Environment: Win2K, Sun JDK1.5.0_05 b05
>     Reporter: Buza Zoltán

>
> MathUtils.round(39.245, 2) results 39.24, however it should be 39.25, with default rounding
mode BigDecimal.ROUND_HALF_UP.
> I found that internally MathUtils.round multiplies the given number by 10^scale.
>  39.245 * 100.0 results 3924.49999...5 , and after this the calculation is not correct
any more.

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