Is there any advantage to specifying the "range" of an integer in VHDL?

Question

Is there any advantage to specifying the range of an integer in VHDL? I know an integer is 32-bit by default.

For example, two counters that will only ever count up to eight (suppose the logic prevents them from going above this number):

signal counter1 : integer range 0 to 8;
signal counter2 : integer;

Won't the tools just optimize the unused bits away in either case according to the logic? So if counter1 and counter2 both only count up to eight then the range command seems pointless.

I only see potential downsides in using "range" (for example I had this problem when I used the "range" command but my range was off by one accidentally). Simulation ignores the "range" you give an integer so if you give it the wrong range then you won't notice this in simulation.

Answer 1

Always specify a range for all natural and integer items, be they signals, variables, ports or generics.

A primary benefit of using a high-level language like VHDL is that the language stops you entering faulty or unwanted data and behaviour. It gets discovered at compilation time, rather than at run-time.

Range-limited values going out of range will cause errors in simulation. This might happen in compilation, might be at run-time. And all designs should be proven in simulation before synthesis, even if it's only basic testing or to observe the signal behaviour.

As an aside, I always use natural wherever possible instead of integer.

natural is a range-limited subtype of integer that can only hold positive values. That also does range limiting because the subtype natural accepts only the positive range of integer.

I find natural strengthens the design, particularly as most designs have a lot of (often all) scalar types that are only positive. All functions you'll encounter operating on integer will work just fine on natural. That might spark some debate but I've done it with great success on all my designs for decades.