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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Question about ordinary fixed point types.
Date: Tue, 17 Aug 2010 17:51:38 +0200
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Date: 2010-08-17T17:51:38+02:00
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sjw writes on comp.lang.ada:
> On Aug 16, 11:03 am, Ludovic Brenta <ludo...@ludovic-brenta.org>
> wrote:
>
>> However and unfortunately, ARM 3.5.9(21) allows an implementation to
>> reject any 'Small that is not a power of two (and, in particular,
>> decimal fixed-point types). I'm not sure whether GNAT supports
>> arbitrary Smalls; from the doc, it seems that it actually rounds them
>> down to a power of two no smaller than 2**(-63).
>
> 2**(-63)! That should be OK in this application, then.

Yes but I suspect it requires 64-bit hardware.  I don't think this would
work on a 16-bit microcontroller.

> The real question for Peter is, what does his target compiler do? If
> it does as GNAT does and allows a delta and matching small of
> ada.numerics.pi / 2 ** 15 then it makes sense to work in your scheme,
> since literal values in the code and values for debug will be in
> radians. If it only alows binary smalls, then (I would) work with
> delta 2 ** (-15) range -1.0 .. 1.0, ie signed fractions of pi, and
> apply the scaling factor as required.

Right.

-- 
Ludovic Brenta.