Re: [vhdl-200x-ft] binary representation of "real"

Jim Lewis wrote:
>> This is far too simplistic a way to look at a floating point
>> number.
>
> We already have:
> procedure READ(L:inout LINE; VALUE: out real; GOOD : out BOOLEAN);
> procedure READ(L:inout LINE; VALUE: out real);
>
> How are your issues addressed by these?

Here you are representing a real number like this:
2.5, -2.5, 25.4E-5
No binary numbers involved, thus no ambiguity.
The problem is one of translating binary to real and back, and
being consistant about it.

>>> A third alternative for real and integer is
>>> to not implement bwrite/bread, owrite/oread,
>>> and hwrite/hread.
>>
>> This sounds like a plan. At least for VHDL-200X-FT.
>
> Agreed. Particularly if there are technical issues
> that we need to solve. However, based on your concerns,
> this would also seem to imply that we cannot do these
> procedures for the proposed fixed point or floating point
> packages as they would need to solve the same issues.

Correct. You would have to do it like this:

HREAD (L : inout LINE; VALUE : out FP32); (or UFIXED, SFIXED, fp, etc).
realvar := to_real (VALUE);

If I overloaded it for real, and you used both the fixed and floating
point packages, you would have an ambiguity problem.

> What is done for both of these would seem to need to be
> consistent.

Yes. Consistency and duplication of functions is the big issue here.

Sounds like I need to come up with a list of what needs to go where.
The basic issue here is that you can't interperate a binary number to
be something unless you have defined it first.

-- 
David W. Bishop dbishop@vhdl.org       All standard disclaimers apply.