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From: jerry@jvdsys.nextjk.stuyts.nl (Jerry van Dijk)
Subject: Re: Long Float Error from Gnat
Date: 1998/10/30
Message-ID: <F1Mz7o.HA@jvdsys.nextjk.stuyts.nl>#1/1
X-Deja-AN: 406906965
References: <3638F49C.E90A401E@easystreet.com>
Organization: * JerryWare *, Leiden, Holland
Newsgroups: comp.lang.ada
Date: 1998-10-30T00:00:00+00:00
List-Id: <comp.lang.ada>

Al Christians (achrist@easystreet.com) wrote:

: I've hit an odd numerical error in a program that I've compiled
: with GNAT 3.10p1 on NT 4 sp3.  I almost can't believe it, so I wonder 
: if anyone else can tell me what's going on.  My number one suspect is 
: that it's a floating point problem in my Pentium Pro.

I'm no expert on this, but there seems to be something strange here.
I would have expected both procedures below to give identical results:

with Ada.Text_IO;
with Ada.Long_Float_Text_IO;

procedure My_Test is

   package Long_Float_IO is new Ada.Text_IO.Float_IO (Long_Float);
    
   procedure Check_Gnat (N : in Long_Float; S : in String) is
      Result : Long_Float;
      Last   : Positive;
   begin
      Ada.Text_IO.Put_Line (N'Img);
      Ada.Long_Float_Text_IO.Put (N);
      Ada.Text_IO.New_Line;
      Ada.Long_Float_Text_IO.Get (S, Result, Last);
      Ada.Text_IO.Put_Line ("Last is" & Last'Img);
      if Result = N then
         Ada.Text_IO.Put_Line ("String equals number");
      else
         Ada.Text_IO.Put_Line ("String does not equal number");
      end if;
      Ada.Text_IO.Put_Line (Result'Img);
      Ada.Long_Float_Text_IO.Put (Result); 
      Ada.Text_IO.New_Line;
      Ada.Text_IO.New_Line;
   end Check_Gnat;

   procedure Check_My (N : in Long_Float; S : in String) is
      Result : Long_Float;
      Last   : Positive;
   begin
      Ada.Text_IO.Put_Line (N'Img);
      Long_Float_IO.Put (N);
      Ada.Text_IO.New_Line;
      Long_Float_IO.Get (S, Result, Last);
      Ada.Text_IO.Put_Line ("Last is" & Last'Img);
      if Result = N then
         Ada.Text_IO.Put_Line ("String equals number");
      else
         Ada.Text_IO.Put_Line ("String does not equal number");
      end if;
      Ada.Text_IO.Put_Line (Result'Img);
      Long_Float_IO.Put (Result); 
      Ada.Text_IO.New_Line;
      Ada.Text_IO.New_Line;
   end Check_My;
   
begin
   Ada.Text_IO.Put_Line ("GNAT:");
   Check_Gnat (1.000000000E-32, "1.000000000E-32");
   Ada.Text_IO.Put_Line ("Mine:");
   Check_My (1.000000000E-32, "1.000000000E-32");
end My_Test;

-- 
-- Jerry van Dijk  | email: jdijk@acm.org
-- Leiden, Holland | member Team-Ada
-- Ada & Win32: http://stad.dsl.nl/~jvandyk