[rules-users] [rules user] different behavior on double type

[Mark Proctor]

On 27/03/2012 03:01, Zeke wrote:
> Whether the comparison is precarious or not should depend on how you 
> handle the literal. If you handle 99.9 as BigDecimal("99.9") which 
> precision can be controlled, you can trust the comparison.
>
> Anyway, since it has different behavior for these two cases, it should 
> be a bug, right? I just want to know it is Drools' bug or MVEL's... If 
> it is MVEL's, I may need ask for MVEL guys' help...
If you need this fixed, you'll need to move to Drools 5.3.

Mark
>
> On 26 March 2012 19:50, Wolfgang Laun <wolfgang.laun at gmail.com 
> <mailto:wolfgang.laun at gmail.com>> wrote:
>
>     4.0.7 is rather old. 5.1.1 and later do not exhibit this behaviour.
>
>     However, it should be noted that comparing double values using == is a
>     precarious approach. For instance, 99.9 (the mathematical number)
>     cannot be represented as a double machine number. Hence, you do not
>     truly test for
>     equality with that number, just with its approximation by some machine
>     number.
>
>     -W
>
>     On 26/03/2012, Zeke <xanadu860122 at gmail.com
>     <mailto:xanadu860122 at gmail.com>> wrote:
>     > Hi, guys:
>     >   I am using Drools 4.0.7. I find a strange behavior. When my LHS is
>     > "Message( varDouble == 99.9 )" and "varDouble" equals "new
>     Double(99.9)",
>     > the condition is true. But when my LHS is "Message(
>     types.doubleType ==
>     > 99.9 )" and the "doubleType" field is also equal to "new
>     Double(99.9)", the
>     > condition is false. I debug the code, and find that:
>     >
>     >   When the LHS is "Message( varDouble == 99.9 )", the logic will
>     handle the
>     > literal 99.9 as *Double.valueOf( "99.9" )*, and the comparison
>     is between
>     > *(new
>     > Double(99.9)).doubleValue(*) and *Double.valueOf( "99.9"
>     ).doubleValue()*,
>     >   When the LHS is "Message( types.doubleType == 99.9 )", the
>     logic is
>     > different from above. The comparison is between *new
>     BigDecimal((Double)
>     > 99.9, MathContext.DECIMAL64)* (which double value is
>     99.90000000000001) and
>     > *new BigDecimal("99.9", MathContext.DECIMAL64)* (which double
>     value is
>     > 99.9).
>     >
>     >   I think we need make things consistent. "varDouble" and
>     > "types.doubleType" are of the same type and value. It doesn't
>     make sense to
>     > have different behavior just because of one field is nesting
>     while the
>     > other is not.  I know Drools is using MVEL to evaluate the
>     condition. But I
>     > am not sure it is a MVEL bug or Drools uses MVEL wrong. It will
>     be much
>     > appreciated if you can give me any comments!
>     >
>
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