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From: Michael Jung <miju@golem.phantasia.org>
Newsgroups: comp.lang.java.programmer
Subject: Re: double == double
Date: Sat, 15 Oct 2016 14:04:35 +0200
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Michael Jung <miju@golem.phantasia.org> writes:
> Eric Sosman <esosman@comcast-dot-net.invalid> writes:
>> On 10/12/2016 8:15 AM, Stefan Ram wrote:
[...]
>>     The problem with comparing double or float values for equality
>> (or inequality) isn't the values themselves, but their "provenance."
>> Calculations that yield identical results when performed with real
>> numbers and their infinite precision may yield different outcomes
>> when finite-precision floating-point values are used instead.  We
>> know, for example, that `ln xy = ln x + ln y' for all positive x,y,
>> yet we cannot rely on `Math.log(x*y) == Math.log(x) + Math.log(y)'.
>> A rearrangement that appears innocuous can produce a result that is
>> slightly different (sometimes more than "slightly!") from that of the
>> original, and it's no simple matter to say which, if either, is
>> "right."
[...] 

More pointedly: don't use "==", when doing arithmetic. One of the
applications of using "==" on doubles may be when they are used as
version numbers such as modelling those of (La)TeX in Java.

(This "argument" does not apply to +0 and -0, though.)

Michael