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From: jboulais@my-deja.com
Subject: Disturbing float conversions...
Date: 2000/05/02
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Date: 2000-05-02T00:00:00+00:00
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I'm seeing something similar, but perhaps a little more disturbing
(Gnat 3.11p and WinNT 4.0).

I've got the following types defined:

   type Long_Float_Type is digits 8 range -32768.000 .. 32767.000 ;

   subtype Angle_Type is Long_Float_Type range -180.00000 .. 179.99451 ;

I find that when I do a 'Image on the 'First and 'Last of Angle_Type, I
get -1.7999872E+02 and 1.7999872E+02 respectively.

If I convert to a long_float (Ada standard, not Long_Float_Type) I get
-1.80000000000000E+02 and 1.79994510000127E+02 respectively, which is
closer, but the 'Last is a little bigger than I defined it to.

If I instantiate Text_IO.Float_IO with Angle_Type, I get -204.7 and
204.7, which really blows me away.



In article <8dfm0q$8nr$1@nnrp1.deja.com>,
  David W. Glessner <david_glessner@my-deja.com> wrote:
> Why does GNAT treat the non-zero constant as 0.0 in the assignment to
> F1 in the following example?  32-bit IEEE floating-point should
> support values down to around 10**-38 (and even down to 10**-45 or
> so for subnormal numbers).
>
> Note that Rational Apex Ada behaves as I expected.
>
> Is there something in Ada that allows the assignment of 0.0 or is
> this a GNAT bug?
>
> -- Test program that shows unexplained (to me at least) GNAT behavior
> for
> -- floating point assignments.
> --
> -- GNAT 3.12p Win98 displays:
> -- 0.00000E+00                           <-- Why does GNAT display
0.0?
> -- 6.66666666666667E-33
> -- 6.66667E-33
> --
> -- Rational Apex 3.0.0b for Solaris (Sparc) displays:
> -- 6.66667E-33
> -- 6.66666666666667E-33
> -- 6.66667E-33
> with Ada.Text_Io;
> procedure Test_Float_Range is
>     C : constant := 6.6666666666666666E-33;
>     F1 : Float := C;
>     F2 : Long_Float := C;
>     F3 : Float := Float (F2);
>     use Ada.Text_Io;
> begin
>     Put_Line (Float'Image (F1));
>     Put_Line (Long_Float'Image (F2));
>     Put_Line (Float'Image (F3));
> end Test_Float_Range;
>
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>

--
-----------------
Jeffrey Boulais


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