Re: understanding floating point types

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Sun, 22 Aug 2010 10:15:24 -0700 (PDT), Ada novice wrote:

> I didn't quite get this part. In my previous example with say a = 2.33
> and b = 3.45. Does Multiplication of a with b mean converting each of
> a and b in model number first and then do the multiplication and
> afterwards approximating the result to the nearest model number? Or
> the multiplication will just be performed with the two numbers as 2.33
> X 3.45 = 8.0385 and then approximating this result to the nearest
> model number?

No, the result is 8.0385 (assuming 32-bit machine numbers). Try this:

with Ada.Text_IO; use Ada.Text_IO;
procedure Test_Float is
   type My_Float is digits 3;
   X : My_Float := 2.33;
   Y : My_Float := 3.45;
begin
   Put_Line ("Model view:" & My_Float'Image (X*Y));
   Put_Line ("The reality:" & Float'Image (Float (X*Y)));
end Test_Float;

It should print:

Model view: 8.04E+00
The reality: 8.03850E+00

When you print the number using My_Float'Image that rounds the machine
number to the nearest model number. In computations and conversions
machine numbers are left untouched.

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