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tech / sci.electronics.design / Re: 0.0 / 0.0 = -NAN ?

SubjectAuthor
* Re: 0.0 / 0.0 = -NAN ?Tabby
+- Re: 0.0 / 0.0 = -NAN ?Joe Gwinn
`* Re: 0.0 / 0.0 = -NAN ?jlarkin
 `- Re: 0.0 / 0.0 = -NAN ?Tabby

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Re: 0.0 / 0.0 = -NAN ?

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Subject: Re: 0.0 / 0.0 = -NAN ?
From: tabbyp...@gmail.com (Tabby)
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 by: Tabby - Sun, 8 May 2022 20:44 UTC

On Saturday, 30 April 2022 at 16:31:51 UTC+1, Skybuck Flying wrote:
> When exception masks are all enabled to stop the processor from throwing floating point exceptions the following calculation produces a somewhat strange result:
>
> 0.0 / 0.0 = -nan
>
> (At least in Delphi).
>
> For now I will assume this is the case in C/C++ as well and with that I mean on x86/x64 which should and seems to be following IEEE 754 floating-point format.
>
> I am a little bit surprised by this and I want/need to know more. Where is this defined that 0.0 / 0.0 should be -NAN ?!?
>
> Problem is with the code, example:
>
> T := 0;
> D := 0.0 / 0.0;
> P := T * D;
>
> This screws up P. instead of P being zero, P is now also -NAN ?!?
>
> I find this very strange but ok.
>
> I guess a simple solution could be to set D to 0 explicitly for this case, is there perhaps another solution ? Maybe some kind of mask or rounding mode so that additional branch is not necessary ???
>
> Bye for now,
> Skybuck.

I can't remember where NAN is from, but it means the answer can not be computed.

Re: 0.0 / 0.0 = -NAN ?

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From: joegw...@comcast.net (Joe Gwinn)
Newsgroups: sci.electronics.design
Subject: Re: 0.0 / 0.0 = -NAN ?
Date: Sun, 08 May 2022 17:47:48 -0400
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 by: Joe Gwinn - Sun, 8 May 2022 21:47 UTC

On Sun, 8 May 2022 13:44:45 -0700 (PDT), Tabby <tabbypurr@gmail.com>
wrote:

>On Saturday, 30 April 2022 at 16:31:51 UTC+1, Skybuck Flying wrote:
>> When exception masks are all enabled to stop the processor from throwing floating point exceptions the following calculation produces a somewhat strange result:
>>
>> 0.0 / 0.0 = -nan
>>
>> (At least in Delphi).
>>
>> For now I will assume this is the case in C/C++ as well and with that I mean on x86/x64 which should and seems to be following IEEE 754 floating-point format.
>>
>> I am a little bit surprised by this and I want/need to know more. Where is this defined that 0.0 / 0.0 should be -NAN ?!?
>>
>> Problem is with the code, example:
>>
>> T := 0;
>> D := 0.0 / 0.0;
>> P := T * D;
>>
>> This screws up P. instead of P being zero, P is now also -NAN ?!?
>>
>> I find this very strange but ok.
>>
>> I guess a simple solution could be to set D to 0 explicitly for this case, is there perhaps another solution ? Maybe some kind of mask or rounding mode so that additional branch is not necessary ???
>>
>> Bye for now,
>> Skybuck.
>
>I can't remember where NAN is from, but it means the answer can not be computed.

It comes from IEEE Std 754, and NaN means only that the answer cannot
be expressed as a real number (versus a poem or a picture), not that
the answer cannot be computed.

..<https://en.wikipedia.org/wiki/IEEE_754>

Joe Gwinn

Re: 0.0 / 0.0 = -NAN ?

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From: jlar...@highlandsniptechnology.com
Newsgroups: sci.electronics.design
Subject: Re: 0.0 / 0.0 = -NAN ?
Date: Sun, 08 May 2022 14:51:52 -0700
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 by: jlar...@highlandsniptechnology.com - Sun, 8 May 2022 21:51 UTC

On Sun, 8 May 2022 13:44:45 -0700 (PDT), Tabby <tabbypurr@gmail.com>
wrote:

>On Saturday, 30 April 2022 at 16:31:51 UTC+1, Skybuck Flying wrote:
>> When exception masks are all enabled to stop the processor from throwing floating point exceptions the following calculation produces a somewhat strange result:
>>
>> 0.0 / 0.0 = -nan
>>
>> (At least in Delphi).
>>
>> For now I will assume this is the case in C/C++ as well and with that I mean on x86/x64 which should and seems to be following IEEE 754 floating-point format.
>>
>> I am a little bit surprised by this and I want/need to know more. Where is this defined that 0.0 / 0.0 should be -NAN ?!?
>>
>> Problem is with the code, example:
>>
>> T := 0;
>> D := 0.0 / 0.0;
>> P := T * D;
>>
>> This screws up P. instead of P being zero, P is now also -NAN ?!?
>>
>> I find this very strange but ok.
>>
>> I guess a simple solution could be to set D to 0 explicitly for this case, is there perhaps another solution ? Maybe some kind of mask or rounding mode so that additional branch is not necessary ???
>>
>> Bye for now,
>> Skybuck.
>
>I can't remember where NAN is from, but it means the answer can not be computed.

Not A Number.

--

Anybody can count to one.

- Robert Widlar

Re: 0.0 / 0.0 = -NAN ?

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Subject: Re: 0.0 / 0.0 = -NAN ?
From: tabbyp...@gmail.com (Tabby)
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 by: Tabby - Wed, 11 May 2022 22:23 UTC

On Sunday, 8 May 2022 at 22:52:03 UTC+1, jla...@highlandsniptechnology.com wrote:
> On Sun, 8 May 2022 13:44:45 -0700 (PDT), Tabby <tabb...@gmail.com>
> wrote:
> >On Saturday, 30 April 2022 at 16:31:51 UTC+1, Skybuck Flying wrote:
> >> When exception masks are all enabled to stop the processor from throwing floating point exceptions the following calculation produces a somewhat strange result:
> >>
> >> 0.0 / 0.0 = -nan
> >>
> >> (At least in Delphi).
> >>
> >> For now I will assume this is the case in C/C++ as well and with that I mean on x86/x64 which should and seems to be following IEEE 754 floating-point format.
> >>
> >> I am a little bit surprised by this and I want/need to know more. Where is this defined that 0.0 / 0.0 should be -NAN ?!?
> >>
> >> Problem is with the code, example:
> >>
> >> T := 0;
> >> D := 0.0 / 0.0;
> >> P := T * D;
> >>
> >> This screws up P. instead of P being zero, P is now also -NAN ?!?
> >>
> >> I find this very strange but ok.
> >>
> >> I guess a simple solution could be to set D to 0 explicitly for this case, is there perhaps another solution ? Maybe some kind of mask or rounding mode so that additional branch is not necessary ???
> >>
> >> Bye for now,
> >> Skybuck.
> >
> >I can't remember where NAN is from, but it means the answer can not be computed.
> Not A Number.

Yup. Though if we are to be pedantic, the correct answers generally are a number, but the CPU is unable to calculate or report them.

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