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From: azimmer@rsa.hisd.harris.com (Alan D Zimmerman)
Newsgroups: comp.lang.ada
Subject: Re: Rational/Verdix Number Bug
Date: 2 Mar 1995 13:49:51 GMT
Organization: Loral Space & Range Systems
Message-ID: <3j4idv$14u@jabba.ess.harris.com>
References: <Mats.Weber-2702951928090001@mlma11.matrix.ch>
Reply-To: azimmer@rsa.hisd.harris.com
NNTP-Posting-Host: yoda.rsa.hisd.harris.com
Date: 1995-03-02T13:49:51+00:00
List-Id: <comp.lang.ada>

In article <Mats.Weber-2702951928090001@mlma11.matrix.ch>, Mats.Weber@matrix.ch (Mats Weber) writes:
> In article <3il66m$ps1@jabba.ess.harris.com>, azimmer@rsa.hisd.harris.com wrote:
> 
> > Well, I am in a perplexing situation.  I tried this when I first heard
> > about the problem and duplicated it with a program like the one attached.
> > I just tried it and  I could not duplicate it.  I am running SunAda 1.1(j)
> > on a SPARC LX.  Below is the test program.
> > 
> > with text_io;
> > procedure test_float is
> >   test : float := 2147.486348;
> >   package flt_io is new text_io.float_io(float);
> > begin
> >   flt_io.put(test);
> >   text_io.new_line;
> >   flt_io.put(test * 2.0);
> >   text_io.new_line;
> >   flt_io.put(test / 2.0);
> > end test_float;
> 
> Here, except in the implicit converion of the literal 2147.486348 from
> universal_real to float, you only use floating point arithmetic (the basic
> operations of the predefined type float), not the compiler's internal
> infinite precision arithmetic, which is where the bug is from my
> understanding of the problem.
No, actually the problem is that I reversed the 3 and the six.  With the 
following program, I get the proper (incorrect) results:

Program:

with text_io;
procedure test_float is
  test : float := 2147.483648;
  package flt_io is new text_io.float_io(float);
begin
  flt_io.put(test);
  text_io.new_line;
  flt_io.put(test * 2.0);
  text_io.new_line;
  flt_io.put(test / 2.0);
end test_float;

Results:

-2.14748364800000E+03
-4.29496729600000E+03
-1.07374182400000E+03

For what it is worth, I have been told that rational knows about this
and that a patch is available.  Thanks to Richard Hash of Team-Ada
who pointed out my problem.

Alan
-- 
|        Alan D. Zimmerman        | Eagle Scout                     |
|   azimmer@rsa.hisd.harris.com   | Scoutmaster T324                |
|-------------------------------------------------------------------|
|     All opinions are solely my own and do not represent Loral     |
|                   On My Honor I will do my best...                |