From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,5f764f1f7822ab9c
X-Google-Attributes: gid103376,public
From: "Dr. Joachim Schr�er" <joachim.schroeer@vs.dasa.de>
Subject: Re: Top 10 Language Constructs (Ada)
Date: 2000/07/18
Message-ID: <8l21od$mkr@newsserv.vs.dasa.de>#1/1
X-Deja-AN: 647835376
References: <8kmjja$l5h$1@pollux.ip-plus.net> <3970F56F.F3A70FAD@icdc.com>
 <01HW.B59982450058903A078EC70C@news.pacbell.net> <39751555.4E40A4A7@lmco.com>
X-Priority: 3
X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2314.1300
Organization: Daimler-Benz Aerospace
X-MSMail-Priority: Normal
Newsgroups: comp.lang.ada
Date: 2000-07-18T00:00:00+00:00
List-Id: <comp.lang.ada>


Bill Brennan <william.c.brennan@lmco.com> schrieb in im Newsbeitrag:
39751555.4E40A4A7@lmco.com...
> David Kristola wrote:
>
> > The other day, i came across a message field in an interface document
> > that i was coding against.  The field is 16 bits, with the high order
> > bit being a sign bit, the next highest order bit has the value 2^1,
> > the third highest bit is 2^0, and so on down to the low order bit,
> > which is 2^(-13).  The note said that the field is 2's complement.
> > No problem....
> >
> >    type Plasma_Volts_Type is delta 0.00012207 range -4.0 .. 3.99987793;
> >    for Plasma_Volts_Type'Size use 16;
>
> Actually, this doesn't compile in GNAT, I presume because it rounds
> Plasma_Volts_Type'Last to something which won't fit in 16 bits.
>
> Besides the fact that this type definition isn't portable (for GNAT
> anyway),
> it doesn't really reflect what you're trying to say.  Without your
> description,
> I would have no idea that 0.00012207 ~= 2^(-13) or that
> 3.99987793 ~= 4 - 2^(-13).
>
> Personally, I think it's clearer to state it as
>
>    type Plasma_Volts_Type is
>       delta  2#000.0_0000_0000_0001#     --  approx 0.00012207
>       range -2#100.0_0000_0000_0000# ..  --        -4
>              2#011.1_1111_1111_1111#;    --  approx 3.99987793
>
>    for Plasma_Volts_Type'Size use 16;
>
> which will compile, and more accurately expresses what is intended.
>
> This ability to express literals fairly transparently using any
> numerical
> base of convenience is yet another reason to value Ada.  (though I'm not
> sure it's important enough to go on my top 10 list.)
>
> -- Bill Brennan

What about this version:

type Plasma_Volts_Type is delta 2.0**(-13) range -4.0 .. 4.0 - 2.0**(-13);
for Plasma_Volts_Type'Size use 16;

And if the required range and the 'delta allow 'delta < 'small you have to
write a rep-clause for 'small like:

for Plasma_Volts_Type'Small use 2.0**(-13);

Joachim Schroeer