Javascript returns -0

Question

I was trying out a simple arithmetic on console where I tried to multiply 0 with -1. Interestingly, I got a -0 as answer, instead of 0.

Screenshot:

Can anyone explain these results?

`0 === -0` is *true* anyways. hmmm, this looks like a webkit console. i'm interested in what other consoles have to say — jeremy, Feb 15 '16 at 07:06
It still violates the fundamental thought that 0 is neither positive nor negative — data_set, Feb 15 '16 at 07:06
related: http://stackoverflow.com/questions/7223359/are-0-and-0-the-same — jeremy, Feb 15 '16 at 07:09
This question explains this http://stackoverflow.com/questions/7223359/are-0-and-0-the-same — Daniel Higueras, Feb 15 '16 at 07:09
@Yoshi - I believe I need not delete this question as per the post - [link]http://meta.stackexchange.com/questions/10841/how-should-duplicate-questions-be-handled. Request you to merge this post wherever necessary. — data_set, Feb 15 '16 at 07:23

score 5 · Answer 1 · answered Feb 15 '16 at 07:08

5

Under the IEEE standard.

Signed zero is zero with an associated sign. In ordinary arithmetic, −0 = +0 = 0. However, in computing, some number representations allow for the existence of two zeros, often denoted by −0 (negative zero) and +0 (positive zero). This occurs in some signed number representations for integers, and in most floating point number representations. The number 0 is usually encoded as +0, but can be represented by either +0 or −0.

answered Feb 15 '16 at 07:08

Fergus

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Oh.. but is it just the way it is? Or can we lose the -0? – data_set Feb 15 '16 at 07:11
Its part of the standard for the comparison of x === y.. look here: http://ecma262-5.com/ELS5_HTML.htm#Section_11.9.6 – Fergus Feb 15 '16 at 07:13

score 2 · Answer 2 · answered Feb 15 '16 at 07:07

2

JavaScript is using IEEE-754, which has both positive and negative zeros.

answered Feb 15 '16 at 07:07

yihangho

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Interesting.. where do we find the use for negative zeros? – data_set Feb 15 '16 at 07:08
I believe there is no important use - it's just a side-effect of the encoding used. – yihangho Feb 15 '16 at 07:09
1

as stated [here](http://stackoverflow.com/a/27074403/704944), one possible reason is so divison by zero can differentiate between -∞ and + ∞ – jeremy Feb 15 '16 at 07:12
@Jeremy Ah I see, interesting. – yihangho Feb 15 '16 at 07:14

Tacocat · Accepted Answer · 2016-02-15T07:25:46.487

Javascript uses IEEE 754 as mentioned above and also,

The IEEE 754 standard for floating-point arithmetic (presently used by most computers and programming languages that support floating point numbers) requires both +0 and −0. Real arithmetic with signed zeros can be considered a variant of the extended real number line such that 1/−0 = −∞ and 1/+0 = +∞; division is only undefined for ±0/±0 and ±∞/±∞.

Negatively signed zero echoes the mathematical analysis concept of approaching 0 from below as a one-sided limit, which may be denoted by x → 0−, x → 0−, or x → ↑0. The notation "−0" may be used informally to denote a small negative number that has been rounded to zero. The concept of negative zero also has some theoretical applications in statistical mechanics and other disciplines.

It is claimed that the inclusion of signed zero in IEEE 754 makes it much easier to achieve numerical accuracy in some critical problems (http://people.freebsd.org/~das/kahan86branch.pdf), in particular when computing with complex elementary functions.

http://www.johndcook.com/blog/2010/06/15/why-computers-have-signed-zero/

score 0 · Answer 4 · answered Feb 15 '16 at 07:11

0

JavaScript uses IEEE 754 standard floating point number system. This system has both positive and negative zeros though they are equal when comparing. It has also positive and negative infinity and "not a number" values.

answered Feb 15 '16 at 07:11

Joni

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Javascript returns -0

4 Answers4