Re: simple question on long_float/short_float

[Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>]

On 10/02/2010 02:11 AM, Nasser M. Abbasi wrote:
>
> 1) So, it seems to me that Ada did use Fortran double in v1. since
> output is different than in v2. Unless I made a mistake in v2. Hence, I
> do not understand why the webpage above said that Gnat would use the
> same types. Can I change v2 to make it output the same as Fortran? I
> assume not, since it is not double to start with.

Sure. Try

type My_Float is digits Interfaces.Fortran.Double_Precision'digits;

or

type My_Float is digits Long_Float'digits;

or even

type My_Float is digits 15;

all of which give My_Float the same "digits 15" declaration as Double_Precision 
and Long_Float.

> I also need to study more about Ada floats and how they work. What I do
> not understand yet, does Ada does use IEEE754 for its floats? Assuming
> it does, then it must do something additional at run-time to obtain the
> result it needs when one uses DIGITS nnn in the type definition for Ada
> float.

Ada compilers typically use an underlying hardware floating-point type to 
implement floating-point type declarations. That is IEEE-754 on many platforms, 
but not all.

-- 
Jeff Carter
"So if I understand 'The Matrix Reloaded' correctly, the Matrix is
basically a Microsoft operating system--it runs for a while and
then crashes and reboots. By design, no less. Neo is just a
memory leak that's too hard to fix, so they left him in ... The
users don't complain because they're packed in slush and kept
sedated."
Marin D. Condic
65