CODEWITHSUNDEEP
swiftnaninfinity
ScottyBlades
ScottyBlades

Reputation: 13983

How to produce negative Nan?

I have a "creative" algorithm I'm working on, and there is a case where I need to return negative Nan.

extension Decimal { 
    func placement(
        between gains: Decimal,
        and losses: Decimal
    ) -> Decimal {
        if gains == losses { 
            return self > gains ? (1 / 0) : (-1 / 0)
        }
        return (self - losses) / (gains - losses)
    }
}

Unfortunately (-1 / 0) produces Nan instead of -Nan.
I've accidentally created -Nan previously, unfortunately, I don't remember how it happened.

Upvotes: 0

Views: 289

Answers (2)

ScottyBlades
ScottyBlades

Reputation: 13983

print(-Double.nan) // produces -nan
print(-Decimal.nan) // produces Nan

I think Decimal might not track signed nan. It doesn't distinguish between positive and negative nan but if it is negative nan, isNan will produce true.

Upvotes: 0

Gereon
Gereon

Reputation: 17844

When something is literally "not a number", how can it have a meaningful sign?

And, from a practical perspective, how do you expect to distinguish "negative NaN" from "NaN"? Decimal.nan == -Decimal.nan is true, as well as Decimal.nan < 0 and -Decimal.nan < 0

let n = Decimal.nan
let nn = -Decimal.nan

print (n < 0) // true
print (nn < 0) // true
print (nn < n) // false
print (n < nn) // false
print (n == nn) // true

Upvotes: 1

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