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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Interfacing Ada with C
Date: Fri, 06 Aug 2010 17:49:14 +0100
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Date: 2010-08-06T17:49:14+01:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Fri, 06 Aug 2010 10:04:24 +0200, Jacob Sparre Andersen wrote:
>
>> Ada novice <posts@gmx.us> wrote:
>> 
>>> Can we change the subtype to Long_Long_Float? This will be of 18
>>> precision digits [...]
>> 
>> That's not guaranteed.  If you want 18 digits, you should declare the
>> type (My_Float?) as:
>> 
>>    type My_Float is digits 18;
>
> Further, practically you should never use subtype in the form
>
>    subtype My_Float is Long_Float;
>
> except for special cases like:
>
>    subtype Non_IEEE_Float is Long_Float range Long_Float'Range;
>
> or
>
>    subtype Non_Negative_Float is Long_Float range 0.0..Long_Float'Last;

Depends what you mean by "practically".

The thought process was, "I'm going to be writing a set of demo cases
which should work for arbitrary floating-point types, I'll call the type
My_Float. Shall I use type My_Float is new ... or subtype My_Float is
...? Doesn't really matter, go for subtype."