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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
 =?utf-8?Q?=29?=
 <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: Re: Question about ordinary fixed point types.
Date: Mon, 16 Aug 2010 00:08:19 +0200
Organization: Ada At Home
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Date: 2010-08-16T00:08:19+02:00
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Hi Peter, nice to see you again,

Le Sun, 15 Aug 2010 23:43:43 +0200, Peter C. Chapin <chapinp@acm.org> a =
 =

=C3=A9crit:

> I have a need to work with ordinary fixed point types. I've read the i=
n
> the reference manual about them (section 3.5.9, for example), and some=

> other things. I still have a few questions. I thought I'd start with o=
ne
> here.
>
> Consider this example:
>
>
> type Angle_Type is delta 0.0005 range -3.1416 .. 3.1416;
> Angle : Angle_Type;
> ...
> Angle :=3D Angle_Type'First;
> while Angle < Angle_Type'Last loop
>   -- Work with Angle here.
>   Angle :=3D Angle + Angle_Type'Small;
> end loop;
OK.


> Aside from Angle_Type'Last does the loop above reliably visit every
> possible value of Angle_Type? By "reliably" I mean "has the desired
> effect on all possible correct Ada implementations." I guess my questi=
on
> is: does Angle + Angle_Type'Small always advance Angle to the next
> machine number in the type?
What do you mean with =E2=80=9Cto the next machine number in the type=E2=
=80=9D ? That this  =

may not advance in some case ?

> I'm using GNAT GPL 2010 and in the example above GNAT appears to be
> using 2**(-11) for Angle_Type'Small.
So a bit less than the desired 0.0005

If the matter is the precise exploration of a precise set of points in a=
  =

range, I may have a silly suggestion (silly in some sense, while not so =
 =

much in some others) : why not use an array of predefined points ? Here,=
  =

you would have an array of 12566 points. Ok, this may seems a big array,=
  =

some design for hight efficiency. But this would come with the benefit o=
f  =

an precise and may be adjustable point by point, set of points. The  =

Quality of this set of point could be precisely evaluated and adjusted. =
 =

This is relevant here, as any way, you will never get exact value, becau=
se  =

as you noticed, the delta does not allow to exactly match the range.

What is the purpose of the exploration ? Sampling at normalized position=
  =

or something of the like ?

I would be very interested to know more about the intended use. This wil=
l  =

learn us a lot of things.


-- =

There is even better than a pragma Assert: a SPARK --# check.
--# check C and WhoKnowWhat and YouKnowWho;
--# assert Ada;
--  i.e. forget about previous premises which leads to conclusion
--  and start with new conclusion as premise.