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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Help with fixed types...insufficient model numbers?
Date: 1997/04/01
Message-ID: <dewar.859934543@merv>#1/1
X-Deja-AN: 229980054
References: <5hrdic$sr@hacgate2.hac.com>
Organization: New York University
Newsgroups: comp.lang.ada
Date: 1997-04-01T00:00:00+00:00
List-Id: <comp.lang.ada>


John Gluth asks about

<<Time_LSB : constant := 0.0000256;

type Time_Type is delta Time_LSB range 0.0 .. 2.0**31 - 1.0;
for Time_Type'Size use 32;
for Time_Type'Small use Time_LSB;>>

There is no model number subtlety here, just a plain obviously wrong
declaration. 32 bits would be enough to fit the given range (just, with
one bit to spare) if the delta were 1.0. Obviously with a delta of
0.0000256 you need far more bits. If you feed this to GNAT, you get:


     1. package j is
     2.    Time_LSB : constant := 0.0000256;
     3.    type Time_Type is delta Time_LSB range 0.0 .. 2.0**31 - 1.0;
     4.    for Time_Type'Size use 32;
           |
        >>> size given (32) for type "Time_Type" too small, minimum is 47

     5.    for Time_Type'Small use Time_LSB;
     6. end;

which seems obviously right for storing numbers in the range you give
with the least significant bit you give. It is not clear why this is
puzzling, so I can't figure out more to say ...