Re: The AFT Attribute

[Bryan@SIERRA.STANFORD.EDU (Doug Bryan)]

Dale brings up a few more interesting points concerning 'Aft.  Consider:

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

Given the definition of Aft, Fix'Aft must return 1.  As Dale points out,
there is no way to exactly represent Fix'Delta in any finite number of digits.
It is interesting to note that Aft is defined in terms of delta, not small.
Thus Aft may not reflect the precision of the actual model numbers of the
type. (?)

Perhaps our question can more precisely be stated as follows:

        What was the rationale for defining Aft to return the smallest 
	positive integer N such that (10 ** N) * T'Delta >= 1?

Why was T'Small not used?  Surely T'Aft is not enough digits to precisely
display the decimal form of a model number of T. (We need
not even consider representation clauses.)  Is Aft sufficient digits
to display the model numbers of T such that one does not display the
same value more than once?

	type T is delta 1.0/16 range 0.0 .. 1.0;
	T'Aft = 2

let us look at some model numbers...

	0.0625	0.125	0.1875	0.25
	
If one were to print these model numbers using 
Put (X, Fore => 2, Aft => T'Aft, Exp => 0), we would see:

	0.06	0.12	0.18	0.25

No values are repeated.  Is this the intended use for 'Aft? 

Has anybody ever used 'Aft?  How  (campers) ?

doug and geoff
-------