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From: =?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne@vajhoej.dk>
Newsgroups: comp.lang.java.programmer
Subject: Re: double == double
Date: Wed, 19 Oct 2016 21:19:45 -0400
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On 10/19/2016 9:16 PM, Arne Vajhøj wrote:
> On 10/19/2016 7:08 PM, Jake Jarvis wrote:
>> Am 19.10.2016 um 22:50 schrieb Jerry Stuckle:
>>> On 10/19/2016 10:36 AM, Jake Jarvis wrote:
>>>> Am 19.10.2016 um 16:26 schrieb Jerry Stuckle:
>>>>> On 10/19/2016 9:32 AM, Eric Sosman wrote:
>>>>>> On 10/19/2016 9:03 AM, Mike Amling wrote:
>>>>>>> If a==0.0 and b==0.0, there's no need to test whether either is
>>>>>>> -0.0.
>>>>>>> The function could be simplified to
>>>>>>>
>>>>>>> public static double max(final double a, final double b) {
>>>>>>>   return a==0.0 && b==0.0 ? 0.0 : (a>=b ? a : b);
>>>>>>> }
>>>>>>
>>>>>>     This would return +0.0 for max(-0.0, -0.0).
>>>>>>
>>>>>
>>>>> PMJI, but how do you figure? a==0.0 && b==0.0 would be false
>>>>
>>>> No.
>>>>
>>>
>>> And why not?  -0.0 != 0.0.
>>>
>>
>> But exactly that is not the case
>>
>> https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.21.1
>>
>> | 15.21.1. Numerical Equality Operators == and !=
>> | [...]
>> | Floating-point equality testing is performed in accordance with the
>> rules of the IEEE 754 standard:
>> | [...]
>> | Positive zero and negative zero are considered equal.
>
> And just for completeness.
>
> IEEE 754 2008 section 5.11 says:
>
> <quote>
> Comparisons shall ignore the sign of zero (so +0 = −0).
> </quote>

It is also relative easy to verify:

public class ZeroZero {
	public static void main(String[] args) {
		double x1 = 0.0;
		double x2 = -0.0;
		System.out.println(Double.doubleToLongBits(x1) == 
Double.doubleToLongBits(x2));
		System.out.println(x1 == x2);
	}
}

Arne