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Re: 0.0 / 0.0 = -NAN ?

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From: use...@revmaps.no-ip.org (Jasen Betts)
Newsgroups: sci.electronics.design
Subject: Re: 0.0 / 0.0 = -NAN ?
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by: Jasen Betts - Sun, 1 May 2022 03:49 UTC

On 2022-04-30, Skybuck Flying <skybuckflying@gmail.com> 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.

You get nan in C see the standards documents.

> 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 ?!?

I guess this was invented by Borland, SFAIK they made all the decisions.

> 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 ?!?

seems reasonable to me.
--
Jasen.

Pray to God, but keep rowing to shore. -- Russian Proverb

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