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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 21:52:18 -0400
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On 10/19/2016 9:47 PM, Jerry Stuckle wrote:
> 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>
>
> So, if that's the case, what does it matter if the operation returns
> +0.0 or -0.0?

Somebody defined the contract for Math.max so that it have to return
-0.0 for (-0.0,-0.0).

It has to fulfill that contract.

I think they could have made the contract different. But somebody at
SUN 20 years ago did not agree.

Arne