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Date: Mon, 16 Aug 2010 07:31:48 -0400
From: "Peter C. Chapin" <chapinp@acm.org>
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Subject: Re: Question about ordinary fixed point types.
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Date: 2010-08-16T07:31:48-04:00
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On 2010-08-16 00:11, Jeffrey Carter wrote:

> Consider this example, which I 1st encountered in 1984:
> 
> with Ada.Text_IO;
> 
> procedure Fixed_Test is
>    type Money is delta 0.01 range -100.0 .. 100.0;
> 
>    Cent : constant Money := Money'Delta;
> 
>    Change : Money := 0.0;
> begin -- Fixed_Test
>    Sum : for I in 1 .. 5 loop
>       Change := Change + Cent;
>    end loop Sum;
> 
>    Ada.Text_IO.Put_Line (Item => Money'Image (Change) );
> end Fixed_Test;
> 
> Typically, the 'Small will be 2#0.000_000_1#, and the program will
> output 0.04. The program adds the machine number closest to 'Delta
> (which is 'Small) each time, not 'Delta, so there's no "snapping" taking
> place, except in the conversion of 0.01 to a machine number of type Money.

The use of Small instead of Delta is the "snapping" I was talking about.
That is, despite the fact that you ask for Money'Delta you end up
advancing Change by Money'Small in your loop.

In my case advancing by Small is the effect I'm after so my earlier loop
where I was adding in Delta each time would have probably still worked
reliably.

Peter