Re: [vhdl-200x] Proposal for improved physical types

On 10/01/15 06:19, David Koontz wrote:
>
> On 10/01/2015, at 9:13 am, Tristan Gingold <tgingold@free.fr> wrote:
>
>> On 08/01/15 22:41, Kevin Thibedeau wrote:
>>>       type frequency is range 0 to physical'high units
>>>        uHz;
>>>        milliHz = 1000 uHz;
>>>        Hz  = 1000 milliHz;
>>>        kHz = 1000 Hz;
>>>        MHz = 1000 kHz;
>>>        GHz = 1000 MHz;
>>>        THz = 1000 GHz; -- Up to 9.2 THz with a 63-bit positive range
>>>      end units;
>>
>> What is wrong with:
>>
>>   type frequency is range 0 to 2**63 -1 units
>>      ...
>>   end units;
>>
>> Should be already supported.
>
> package physical is
>      type FREQ is range 0 to 2**63 -1 units  -- line 209
>          Hz;
>          kHz = 1000 Hz;
>          MHz = 1000 kHz;
>          GHz = 1000 MHz;
>          THz = 1000 GHz;
>      end units;
>
> ghdl -a top_physicaltest.vhdl
> top_physicaltest.vhdl:209:30: arithmetic overflow in static expression
> top_physicaltest.vhdl:209:26: range constraint for a physical type must be static
>
> (ghdl-0.31).
>
> Analyzes successfully with 2**62 -1, and that sounds like an implementation limit.

Yes, because 2**63 is of type universal integer (a 64 bit type in ghdl), 
but out of the bounds.  Would work if you write the whole number.

(Ada with its arbitrary precision for universal types at compile time 
only doesn't have such issue - and yes, I think this is the best model: 
arbitrary precision at execution time would be a bad idea from a 
performance point of view).

Tristan.




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