Re: Assignment of small Float values

["Robert I. Eachus" <rieachus@earthlink.net>]

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).

    Jumping in where angels fear to tread--because it is so difficult to
explain the "correct" answer:

    First, the realistic answer:  It is probably a bug.

    Second, the language lawyerly answer:

        If you did not compile in strict mode, you cannot reason about
the arithmetical model at all.  If this problem occurs in strict mode,
and if the exponent is greater than S'Model_Emin (not T'Machine_Emin),
then the compiler fails to comply with the standard.  If there are in
fact no model numbers between 6.6666666666666666E-33 and 0.0, then the
implementation is valid.  (The trickiness here is that for some floating
point representations without gradual underflow, there is a significant
gap in the model numbers on either side of zero.  In other words, the
gap between the model number just above zero and zero is much greater
than the gap between that model number and the model number next above
it.)