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From: =?UTF-8?B?TWFya3VzIFNjaMO2cGZsaW4=?= <no@spam.spam>
Newsgroups: comp.lang.ada
Subject: Re: Fixed point constants issue
Date: Fri, 24 Sep 2010 16:43:29 +0200
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Date: 2010-09-24T16:43:29+02:00
List-Id: <comp.lang.ada>

Forgive me for resurrecting an old thread, but when trying to understand 
the issue, I came up with more questions...

Am 13.09.2010 22:35, schrieb Jeffrey Carter:

> Note that this changed between Ada 83 and Ada 95. In Ada 83, the expression
> is evaluated exactly at compile time using universal_real, just as for the
> named number. In Ada 95, this was changed to use the "*" function defined
> for Altitude.

Are you sure about that? Because I compiled and ran the following program 
with an Ada 83 compiler (DEC Ada) and I got a different result. Note that I 
modified the delta to 0.5 to avoid any issues resulting from delta /= small.

---%<---
with TEXT_IO; use TEXT_IO;

procedure FIXED_POINT
is
    type ALTITUDE is delta 0.5 range 0.0 .. 50_000.0;

    package ALTITUDE_IO is new FIXED_IO (ALTITUDE);

    FEET_PER_METER : constant := 0.3048;
    HEIGHT         : constant := 10; -- Feet

    TEN_FEET_1 : constant          := HEIGHT * FEET_PER_METER;
    TEN_FEET_2 : constant ALTITUDE := HEIGHT * FEET_PER_METER;
begin
    ALTITUDE_IO.PUT (TEN_FEET_1); NEW_LINE; -- gives 3.0
    ALTITUDE_IO.PUT (TEN_FEET_2); NEW_LINE; -- gives 5.0 (*)
end FIXED_POINT;
--->%---

(*) This certainly looks like FEET_PER_METER is converted to ALTITUDE 
before doing the multiplication.

Another question regarding the implicit conversion from universal_real to 
ALTITUDE: Does ARM83-3.5.6 apply here? And what does this mean: "If the 
universal_real value is a safe number, the implicit conversion delivers the 
corresponding value; if it belongs to the range of safe numbers but is not 
a safe number, then the converted value can be any value within the range 
defined by the safe numbers next above and below the universal_real value." 
Is the compiler free to convert FEET_PER_METER to either 0.0 or 0.5?

Regards,
Markus