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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: loop problem with exit condition
Newsgroups: comp.lang.ada
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Date: Sun, 26 Sep 2010 11:10:24 +0200
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Date: 2010-09-26T11:10:24+02:00
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On Sun, 26 Sep 2010 01:16:37 -0700 (PDT), Ada novice wrote:

> One small mistake: Inner range is divided into 100 steps (not 300) as
> I wrote. But the number is irrelevant and the code should
> work fine with all limits.

You have accumulation of errors, which typical when floating-point numbers
of same sign are summed. As the sum grows, addition looses more and more of
its precision. There are several strategies how to handle this problem. But
in your case the simplest way to remove bias would be to multiply the step:

with Ada.Text_IO;             use Ada.Text_IO;
with Ada.Long_Float_Text_IO;  use Ada.Long_Float_Text_IO;

procedure Try is
   Count : Integer;
   Outer : Long_Float;
   Outer_Start : constant := -44.88;
   Outer_Step  : constant := (67.32 - Outer_Start) / 299.0;

   Inner : Long_Float;
   Inner_Start : constant := 0.001;
   Inner_Step  : constant := (0.35 - Inner_Start) / 99.0;
begin
   Count := 0;
   Outer := Outer_Start;
   for I in 1..300 loop
      Outer := Outer_Start + Outer_Step * Long_Float (I - 1);
      for J in 1..100 loop
         Count := Count + 1;
         Inner := Inner_Start + Inner_Step * Long_Float (J - 1);
      end loop;
   end loop;
   Put ("Inner after loop is (should be 0.35) ");
   Put (Item => Inner, Fore => 3, Aft  => 3, Exp  => 0);
   New_Line;
   Put_Line ("Count after loop is" & Integer'Image (Count));
end Try;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de