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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: How to byte swap an IEEE Float?
Date: Fri, 01 Jul 2005 05:51:22 +0100
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Date: 2005-07-01T05:51:22+01:00
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Stephen Leake <stephen_leake@acm.org> writes:

> Ok. So you have some code that generates a NaN, sends it over a
> network or something, and then some Ada code wants to store it in a
> Float value, still as a NaN.

I understood that the problem was

   read a big-endian value from a file into a little-endian float
   byte-swap the float

Clearly you're at risk until the swap. Personally I'd read into an
array 1 .. 4 of Unsigned_8, swap, unchecked convert to Float ...

> Unchecked_Conversion should support that. I'm not quite clear what
> will happen when you try to use the value or even assign the value;
> you'll probably get Constraint_Error. You might try 'Valid.

> The Ada model of floating point numbers does _not_ include NaN's, nor
> infinities. 

You can generate them, but they are not 'Valid. With GNAT, you don't
get a Constraint_Error if you use type Float, but you do if you use

  subtype Checking_Float is Float range Float'First .. Float'Last;

-S