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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 21:16:57 -0400
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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>

Arne