Indeed, when doing floating point math, you cannot check the values for
equality, they will rarely be, you have to check whether the difference in
between them is less than the error you are willing to accept. Floating
point numbers are usually an approximation to the actual value and
intermediate operations might pile up errors in each approximation in
different ways.
As an example,
$third = 1/3;
$third will contain 0.33333 up to a certain number of digits, but it won't
last forever, as it should, theoretically.
Now,
$third * 3 == 1
will be false, but:
define('MAXERR',0.0000001);
abs($third * 3 - 1) < MAXERR
will be true.
MAXERR is the error you are willing to accept in your calculations, for
example, if you are using cents, give it a couple of extra positions so that
roundings don't creep up to significant cents, that is, use MAXERR = 0.0001
or thereabouts.
Satyam
----- Original Message -----
From: "Ezra Nugroho" <enugroho@xxxxxxxxxxxxxxx>
It is not always possible to precisely represent decimal values as a
float type in binary. In these cases, the value that you have is either
slightly bigger or slightly smaller than the actual.
In your specific problem, you have two values that are not equal, but
very similar. Therefore you get a small negative value when subtracting
them.
You just have to keep this fact in mind whenever you want to do high-
precision computing.
On Tue, 2006-03-28 at 15:30 -0600, Jay Blanchard wrote:
[snip]
I've got a strange problem here.
I'm subtacting one variable from another, both of type "double" and if
they are the same, instead of getting a result of 0, I get something
like -9.99200722163E-016
Is this a bug or am I doing something wrong here?
[/snip]
From all of the information that you sent in your post I'd say that
you're doing something wrong here.
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