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Re: double == double

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  Re: double == double Arne Vajhøj <arne@vajhoej.dk> - 2016-10-14 22:33 -0400

#35760 — Re: double == double

On 10/12/2016 8:15 AM, Stefan Ram wrote:
>   Sometimes it is taught that it makes no sense to compare
>   two double values with »==«.

Yes.

Good rule of thumb.

It is very rare that == between two doubles are a good solution for
the problem at hand.

>   But what about this function?
>
> public static double max( final double a, final double b)
> { return
>   a == 0.0 && b == 0.0 && java.lang.Double.doubleToRawLongBits( a )
>   == Double.doubleToRawLongBits( -0.0d )? b : a >= b ? a : b; }
>
>   which tries to return positive zero if one argument is
>   positive zero and the other one negative zero?

That is what Math.max does, but I find it difficult to see
any practical usage from that.

>   It seems that there are special cases when a comparison
>   of double values with »==« is appropriate. I have observed
>   that this is usually the case when comparing with »0.0« -
>   another example would be avoiding to divide by 0.0.

I think a large part of these cases will turn out not to be good
code.

Arne

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