double

[normd@online.knorrassociates.com]

I'm trying to multiply two doubles and assign the result to a double as well.
But it seems the result is rounded up.
x = 907.18474
y = 2.2046226218487 757
the result I calculate 1999.9999999999 99902722818
But this is calculated to be 2000.0.
I looked up double and it is specified as follows;
double ±5.0 × 10−324 to ±1.7 × 10308
Precision: 15-16 digits
What am I missing here?

[Scott M.]

Re: double

What are you using to display the answer? Have you tried applying a custom
numerical format to the output field? One that specifies the number of
decimal places to show?


"normd@online.k norrassociates. com"
<normdonlinekno rrassociatescom @discussions.mi crosoft.com> wrote in message
news:FD644147-494A-4B6F-8C3A-0E793712C989@mi crosoft.com...[color=blue]
> I'm trying to multiply two doubles and assign the result to a double as
> well.
> But it seems the result is rounded up.
> x = 907.18474
> y = 2.2046226218487 757
> the result I calculate 1999.9999999999 99902722818
> But this is calculated to be 2000.0.
> I looked up double and it is specified as follows;
> double ±5.0 × 10?324 to ±1.7 × 10308
> Precision: 15-16 digits
> What am I missing here?[/color]

[Jon Skeet [C# MVP]]

Re: double

normd@online.kn orrassociates.c om
<normdonlinekno rrassociatescom @discussions.mi crosoft.com> wrote:[color=blue]
> I'm trying to multiply two doubles and assign the result to a double as well.
> But it seems the result is rounded up.
> x = 907.18474
> y = 2.2046226218487 757
> the result I calculate 1999.9999999999 99902722818
> But this is calculated to be 2000.0.
> I looked up double and it is specified as follows;
> double ?5.0 ? 10?324 to ?1.7 ? 10308
> Precision: 15-16 digits
> What am I missing here?[/color]

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

You're actually multiplying
907.18474000000 003343302523717 284202575683593 75
by
2.2046226218487 756653985343291 424214839935302 734375

The result of that is

1999.9999999999 999450401001164 764179157374400 704388006048267 67859378833
236405625939369 20166015625

The two exactly representable numbers closest to that are
1999.9999999999 997726263245567 679405212402343 75
and
2000

2000 is closer to the actual number than the number slightly lower than
it, hence your result.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too