Hi quick question about doubles In Kotlin `0 1 + 0 1 + 0 1 + kotlinlang #getting-started

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Tony Blundell

01/01/2021, 11:01 PM

Hi, quick question about doubles. In Kotlin,

0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 < 0.8

evaluates as true, because the left-hand side is actually 0.79r instead of 0.8. What's the best way of dealing with this? I guess I could convert to a string and back, but that feels a little 'hacky'. Is there a better way?

zpearce

01/01/2021, 11:05 PM

If you need accuracy, BigDecimal is the way to go

👍 1

ephemient

01/01/2021, 11:25 PM

https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

if you're going to stick with floating point, all comparisons should have an error bound

also it's not quite 0.79r or 0.8; neither is exactly representable in floating point

Tony Blundell

01/01/2021, 11:33 PM

👍 thanks both

Denis Korotchenko

01/02/2021, 10:30 AM

You can also try to use construction like this: if (abs(res-pred) < eps)... where eps is a constant like 10^(-7) etc.

elizarov

01/13/2021, 10:07 AM

Highly recommended read: https://floating-point-gui.de/

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