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

[Michael Anstis]

FYI, 5.4 (beta 2) allows you to use B and I as BigDecimal and BigInteger
respectively in LHS DRL (and RHS if using MVEL) so you can write:

MyFact( myBigDecimal == 99.9B )

sent on the move

On 27 Mar 2012 08:16, "Wolfgang Laun" <wolfgang.laun at gmail.com> wrote:

> On 27/03/2012, Zeke <xanadu860122 at gmail.com> 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.
> >
>
> Wait a sec: primarily, you are testing a double, and this is where
> some unavoidable imprecision is introduced. These are some doubles
> close
> to 99.9:
>
> a     99.899999999999990000 0x1.8f99999999999p6
> b     99.900000000000000000 0x1.8f9999999999ap6
> c     99.900000000000020000 0x1.8f9999999999bp6
>
> a < 99.9 is the true value truncated, b > 99.9 is rounded  (the next
> binary digit being 1). There just isn't a double == 99.9. (Don't be
> confused by b's printed value.)
>
> The BigDecimal value 99.90000000000001 you have observed is due to
> rounding the result of new BigDecimal( (double)99.9 ), i.e.
>    99.900000000000005684341886080801486968994140625
>
> It's easy to see that a better value is obtained by using a String value:
>    new BigDecimal( "99.9" )
> but I don't know whether your Drools version would let you write
> doubleValue == "99.9".
>
>
> If you want/have to stick with 4.x you might use public static final
> doubles defined in some Java class instead of the magic 99.9. This
> should avoid the sidestep into BigDecimal and the ensuing conversion
> confusion.
>
> -W
> _______________________________________________
> rules-users mailing list
> rules-users at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.jboss.org/pipermail/rules-users/attachments/20120327/1871184f/attachment.html