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From: sjw <simon.j.wright@mac.com>
Newsgroups: comp.lang.ada
Subject: Re: Question about ordinary fixed point types.
Date: Tue, 17 Aug 2010 07:37:21 -0700 (PDT)
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Date: 2010-08-17T07:37:21-07:00
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On Aug 16, 10:23=A0am, Simon Wright <si...@pushface.org> wrote:
> "Peter C. Chapin" <chap...@acm.org> writes:
>
> > I need to do real number computations on a microcontroller without a
> > floating point unit. I believe the various numeric quantities that I
> > need can be normalized into fairly narrow ranges so it seemed to me tha=
t
> > this is a perfect application of fixed point types. The compiler stores
> > the numbers as integers representing the appropriate multiple of Small.
>
> > I'm not using GNAT on the microcontroller but if the Ada compiler I am
> > using does the same thing as GNAT it will be able to fit Angle_Type as
> > it is currently defined into a 16 bit word and compute with it using
> > integer instructions. In my environment that is essential.
>
> It would be very normal in that sort of environment to work in binary
> fractions of 180 degrees.
>
> with Ada.Numerics;
> with Ada.Text_IO; use Ada.Text_IO;
> procedure Angles is
> =A0 =A0Angle_Type_Delta : constant :=3D Ada.Numerics.Pi * 2.0 ** (-16);
> =A0 =A0type Angle_Type is
> =A0 =A0 =A0delta Angle_Type_Delta
> =A0 =A0 =A0 =A0range -Ada.Numerics.Pi / 2 .. Ada.Numerics.Pi / 2;

Eep.

   Angle_Type_Delta : constant :=3D Ada.Numerics.Pi * 2.0 ** (-15);
   type Angle_Type is
     delta Angle_Type_Delta
       range -Ada.Numerics.Pi .. Ada.Numerics.Pi;

> =A0 =A0for Angle_Type'Small use Angle_Type_Delta;
> =A0 =A0for Angle_Type'Size use 16;