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From: drw@cullvax.UUCP (Dale Worley)
Newsgroups: net.lang.ada
Subject: Re: The AFT Attribute
Message-ID: <350@cullvax.UUCP>
Date: Mon, 22-Sep-86 16:38:18 EDT
Article-I.D.: cullvax.350
Posted: Mon Sep 22 16:38:18 1986
Date-Received: Mon, 22-Sep-86 21:25:36 EDT
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Organization: Cullinet Software, Inc., Westwood, MA
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> I'm confused again.  In the LRM, 3.5.10(9) states (parenthetically)
> that the value of the AFT attribute is the smallest positive N
> such that (10 ** N) * T'DELTA >= 1.0.  Now, 3.5.10(15) states that
> the value returned by AFT depends only on T'DELTA. [3.5.10(15) is
> a "note".]
> 
> Can these two paragraphs imply a cohesive semantics for the AFT
> attribute?  Using 3.5.10(9) on the following type:
> 
>   type Fix is delta 1.0 / 16.0 range 0.0 .. 1.0;
> 
> The smallest value N that satisfies the equation is 2.  But how can
> one represent 1.0 / 16.0 accurately in two decimal digits?
> [1.0 / 16.0 = 0.0625]
> 
> What am I missing here?

The point is that T'AFT digits is not guaranteed to be enough to
represent the values of type T.  (Consider

	type Fix is delta 1.0 / 3.0 range 0.0 .. 1.0;

No number of digits is sufficient!)  All you are guaranteed is that
the delta is >= (10 ** -T'AFT).

Now, what 'AFT is good for, I don't rightly know...  Any guesses,
campers?

Dale