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Date: Wed, 1 Jun 2011 20:43:44 +0800
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To: internals@lists.php.net
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Subject: Re: [PHP-DEV] INF behavior
From: datibbaw@php.net (Tjerk Anne Meesters)

On Wed, Jun 1, 2011 at 6:04 AM, Gustavo Lopes <glopes@nebm.ist.utl.pt> wrote:
> On Tue, 31 May 2011 22:41:36 +0100, Hannes Landeholm <landeholm@gmail.com>
> wrote:
>
>>> Agree with Derick, strictly speaking, in maths science, INF != INF.
>>
>> I disagree,based on quote from
>> http://compilers.iecc.com/comparch/article/98-07-134:
>>
>> "Since a projective infinity doesn't have a sign, comparing a floating
>> point value other than infinity to a projective infinity is unordered.
>> However, a projective infinity is equal to itself."
>>
>
> Yes, as I argued, for purposes of IEEE 754, it's certainly the case that INF
> = INF.
>
> This may not be true for certain meanings of "infinity" or notions of
> ordering, but we have a standard for floating point arithmetic with
> well-defined terms and rules which we ought to follow.
>
> As a curiosity, Mathematica defines the result of Equal[Infinity, Infinity]
> and Equal[Overflow, Overflow], but not for ComplexInfinity or Indeterminate
> (similar to NaN):
>
> In[1]:= ComplexInfinity == ComplexInfinity
> Out[1]= ComplexInfinity == ComplexInfinity
> In[2]:= Infinity == Infinity
> Out[2]= True
> In[3]:= Overflow == Overflow
> Out[3]= True
> In[4]:= Indeterminate == Indeterminate
> Out[4]= Indeterminate == Indeterminate

That, and the fact that "a != b" should always imply "a !== b" imo.
And if you must compare with SQL it would be something more akin to
"is_infinite(a)"

>
> --
> Gustavo Lopes
>
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>



-- 
--
Tjerk