What is "-0.0"

Discussion in 'Java' started by Morgan Cheng, Oct 13, 2007.

1. Morgan ChengGuest

In java 6.0, I have below code.
double x = 0.0;
double y = -10.0;
double z = x / y;
System.out.println("z = " +z);

The result is "-0.0". This is wired, why it is negative zero?

Morgan Cheng, Oct 13, 2007

2. Richard ReynoldsGuest

"Morgan Cheng" <> wrote in message
news:...
> In java 6.0, I have below code.
> double x = 0.0;
> double y = -10.0;
> double z = x / y;
> System.out.println("z = " +z);
>
> The result is "-0.0". This is wired, why it is negative zero?
>

http://en.wikipedia.org/wiki/−0_(number)

Richard Reynolds, Oct 13, 2007

3. Patricia ShanahanGuest

Morgan Cheng wrote:
> In java 6.0, I have below code.
> double x = 0.0;
> double y = -10.0;
> double z = x / y;
> System.out.println("z = " +z);
>
> The result is "-0.0". This is wired, why it is negative zero?
>

I agree that it is weird, but there are reasons why IEEE 754 floating
point arithmetic distinguishes positive and negative zero.

A zero may be a stand-in for a number of very small absolute magnitude.
There are some algorithms where intermediate results overflow and
underflow, but the final answer is representable.

Preserving the sign on underflow, and through arithmetic using a zero,
also preserves the sign on division by the result of the underflow,
leading to the correct choice between positive and negative infinity.

Patricia

Patricia Shanahan, Oct 13, 2007
4. Stefan RamGuest

Stefan Ram, Oct 13, 2007
5. Roedy GreenGuest

On Sat, 13 Oct 2007 05:06:35 -0700, Morgan Cheng
<> wrote, quoted or indirectly quoted someone
who said :

>
>The result is "-0.0". This is wired, why it is negative zero?

Because floating point has both a positive and negative 0, signed
magnitude, unlike ints. see http://mindprod.com/jgloss/ieee754.html
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