[5400] in java-interest
Re: Numbers
daemon@ATHENA.MIT.EDU (Terence Chr Haddock)
Wed Feb 7 18:08:16 1996
Date: Wed, 7 Feb 1996 16:22:10 -0500 (EST)
From: Terence Chr Haddock <haddock@UDel.Edu>
To: Jill Shermer <jshermer@BASISinc.com>
cc: pat@icon-stl.net, java-interest@java.sun.com
In-Reply-To: <9602071637.AA05212@nemesis.BASISinc.com>
On Wed, 7 Feb 1996, Jill Shermer wrote:
I am noticing this same effect. I am running Netscape 2.0b6 under
Windows NT with the Windows NT 1.0 version of javac. When I use doubles
that are more than 6 digits long (including digits after the decimal
point), it appears to be rounding the last digits off to make it fit to
six decimals. But, it sometimes appears to round up at the 3 instead of
the 5! Here's the effects that I have seen: (I can't give you code,
because I got this output using my spreadsheet applet, which uses doubles
internally):
100000.2*2 = 200000
100000.3*2 = 200001
100000.6*2 = 200001
But now, if we take 100000.5 * 2, and divide that by 20 we get:
(100000.5*2)/20=10000
Now take, 100000.6 * 2, and divide that be 20 we get:
(100000.6*2)/20=10000.1 !
Why did it round up at .6 instead of .5?
It looks to me like toString() is truncating the doubles to six
digits, but is using some wierd algorithm for doing so. Any comments from
the Java team?
- Terence C Haddock
haddock@udel.edu
> > Subject: Re: Numbers
> > MIME-Version: 1.0
> > X-Info: To unsubscribe, send 'unsubscribe' to java-interest-request@java.sun.com
> >
> >
> > On Tue, 6 Feb 1996, Jill Shermer wrote:
> >
> > > 2. How do you avoid loss of precision with doubles?
> > >
> > > For example, if a = 300000.33,
> > > b = 2,
> > > c = a*b,
> > >
> > > how do you make sure c = 600000.66, not 600001?
> > > Is this avoidable?
> >
> > It should be more clear if you declare the types of your variables.
> > Unless you perform an explicit cast, the type of c will have to be double
> > and the value will be 600000.66
> >
>
> I have explicitly declared a,b, and c to be doubles in my Java code, and
> I still lose precision.
>
> -Jill
>
>
> -
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