Floating Point Calculation Problem

29 Sep 2006 8:16 PM

DJ

Hello,

In an application that worked fine until recently I have started to have
problems with calculations involving two doubles. For example: -24.708 +
26.0 = 1.2920000000000016, however, -24.708 + 8.0 = -16.708. What would
cause this? I don't think the numbers are so large that it would be the
usual floating point calculation error because of rounding. How can I fix
it? I'd rather not change every calcuation in my program to include a
math.round...

..Net Framework 1.1 version 1.1.4322 SP1
Visual Basic - Visual Studio .Net 2003
Windows XP

Thanks,

29 Sep 2006 9:42 PM

Chris Saunders

The size of your numbers are not relevant to this issue.
Here is an URL with an article you should probably read if you wish to
better
understand this issue: http://docs.sun.com/source/806-3568/ncg_goldberg.html

I know nothing about your application but you may indeed need something
along the lines you suggested.

Regards
Chris Saunders

Show quote

"DJ" <D*@discussions.microsoft.com> wrote in message
news:9B524941-7ACC-4D2F-9773-B12C9AB48AB9@microsoft.com...
> Hello,
>
> In an application that worked fine until recently I have started to have
> problems with calculations involving two doubles. For example: -24.708 +
> 26.0 = 1.2920000000000016, however, -24.708 + 8.0 = -16.708. What would
> cause this? I don't think the numbers are so large that it would be the
> usual floating point calculation error because of rounding. How can I fix
> it? I'd rather not change every calcuation in my program to include a
> math.round...
>
> .Net Framework 1.1 version 1.1.4322 SP1
> Visual Basic - Visual Studio .Net 2003
> Windows XP
>
> Thanks,

30 Sep 2006 6:13 PM

Jon Skeet [C# MVP]

DJ <D*@discussions.microsoft.com> wrote:

> In an application that worked fine until recently I have started to have
> problems with calculations involving two doubles. For example: -24.708 +
> 26.0 = 1.2920000000000016, however, -24.708 + 8.0 = -16.708. What would
> cause this? I don't think the numbers are so large that it would be the
> usual floating point calculation error because of rounding. How can I fix
> it? I'd rather not change every calcuation in my program to include a
> math.round...

See http://www.pobox.com/~skeet/csharp/floatingpoint.html

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

1 Oct 2006 4:12 AM

Nick Malik [Microsoft]

"DJ" <D*@discussions.microsoft.com> wrote in message
news:9B524941-7ACC-4D2F-9773-B12C9AB48AB9@microsoft.com...
> Hello,
>
> In an application that worked fine until recently I have started to have
> problems with calculations involving two doubles. For example: -24.708 +
> 26.0 = 1.2920000000000016, however, -24.708 + 8.0 = -16.708. What would
> cause this?

I don't see a problem here. Why do you?

> I don't think the numbers are so large that it would be the
> usual floating point calculation error because of rounding.

Who said size has anything at all to do with this calculation? Rounding
doesn't just happen for very large numbers. It happens for all of them.

> How can I fix
> it?

Decimal datatype

Show quote

> I'd rather not change every calcuation in my program to include a
> math.round...
>
> .Net Framework 1.1 version 1.1.4322 SP1
> Visual Basic - Visual Studio .Net 2003
> Windows XP
>
> Thanks,