NaN different from NaN in Go?

Question

Can anyone explain why this happens? http://play.golang.org/p/QTaHpUm5P7

Apologies for not pasting the code here as well but I'm on mobile ATM.

I know I could use math.IsNaN() but I'm using the comparison operator for all my tests cases.

possible duplicate of [What is the rationale for all comparisons returning false for IEEE754 NaN values?](http://stackoverflow.com/questions/1565164/what-is-the-rationale-for-all-comparisons-returning-false-for-ieee754-nan-values) — fuz, Feb 19 '14 at 12:25

paxdiablo · Accepted Answer · 2014-02-19T02:14:37.823

9

Generally, NaN is not considered equal to any number, including itself. That's because it represnts a number outside the range of representation.

Hence there's no guarantee that you don't have two different numbers outside the representation, such as 0 / 0 and the square root of -1.

In fact, many systems rely on this inequality to implement isNan() as something like:

define isNaN(x):
    return x != x

From the NaN Wikipedia page, IEEE 754 defines that:

edited Feb 19 '14 at 02:14

answered Feb 19 '14 at 02:08

paxdiablo

1

well, guess how isNan() is implemented in Go? http://golang.org/src/pkg/math/bits.go?h=IsNaN#L31 – rob74 Feb 19 '14 at 15:54

score 4 · Answer 2 · edited May 23 '17 at 11:57

4

This is a duplicate of What is the rationale for all comparisons returning false for IEEE754 NaN values? - NaN never equals itself in IEE754, the linked answer explains why.

edited May 23 '17 at 11:57

Community

answered Feb 19 '14 at 02:08

bazzargh

2 Answers2