RE: {Spam?} Re: EXTERNAL: [vhdl-200x] A compromise about modular type, boolean operations, integers...

Tristan,

You can write your own resolution function, and declare a resolved subtype using it. The function takes an unconstrained array of integers (the driven values), and returns a value of the same type or subtype thereof.

subtype nat4 is integer range 0 to 3;
function modular4(arg: integer_vector) return nat4 is
  variable temp : integer := integer'low;
begin
  for I in arg'range loop
    temp := maximum(temp, arg(i));
  end loop;
  return temp mod 4;
end function modular4;

subtype mod4 is modular4 integer;
	
signal mysig : mod4;

mysig <= 5; -- takes the value (5 mod 4) = 1

In your counter-example, if s were of the resolved subtype mod4, then s could not have had the value integer'high in the first place, so s + 1 could not exceed integer'high, and there would be no error.

However, s <= integer'high + 1 would generate an error in the "+" function, and without functions knowing the subtype for the return value from the context, so would any other solution that is interoperable with standard integers.


Andy D Jones
Electrical Engineering
Lockheed Martin Missiles and Fire Control
Dallas TX



-----Original Message-----
From: owner-vhdl-200x@eda.org [mailto:owner-vhdl-200x@eda.org] On Behalf Of tgingold@free.fr
Sent: Wednesday, October 22, 2014 10:53 PM
To: vhdl-200x@eda.org
Subject: {Spam?} Re: EXTERNAL: [vhdl-200x] A compromise about modular type, boolean operations, integers...

> There is still another alternative:
> 
> For signals, we can create modular integers today, using a resolution 
> function.

Not, that's not correct.  Whatever the resolution function resolv in that excerpt, you cannot have a modular behaviour:

  signal s : resolv integer;
..
  s <= s + 1;

when 's' has the integer'last value, you will get an error.  And that error occurs in the '+'.

If you don't agree with that, please provide a counter-case.

Tristan.

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