Re: [vhdl-200x] RE: Modular types

I am in agreement with most of this proposal. However, I feel we are getting 
confused between defining a modular integer type and its implementation within a 
compiler.

Integers, as a VHDL type, have no comprehension of shift functions or logical 
functions. These imply vectors, or how we would naturally implement integers. 
They do have mathematical equivalents, e.g. shift -> 2**(±N) assuming we are 
mapping to a binary vector such as UNSIGNED.

As such they should be added as overloads to the Numeric_Std and Numeric_Bit 
packages.


Now, most explanations of modular types start with the analogy to time - hours, 
minutes, and seconds and that they are examples of modulo 12 types  i.e:

     1, 2, 3,....11, 12.

and then they very quickly normalize this type to:

     0, 1, 2,....10, 11.

and then start explaining modular types.

In fact there are many (infinite) subtypes of this range length that are of a 
modulo 12 subtype.

So in order to perform the arithmetic in normal INTEGER, we will need to first 
normalize any modular types and caste to INTEGER:

     int_object = INTEGER(mod_object - MOD_TYPE'low)    ....... or do we???

and then after performing the integer calculation, the resolution function will 
need to convert it back to its modulo type and reverse-normalize at the 
assignment point:

     mod_object = MOD_TYPE(int_object mod MOD_TYPE'length) + MOD_TYPE'low

That is my concept of how we should handle modular type arithmetic.


Regards,

Brent.



On 28/07/2014 09:07, Martin.J Thompson wrote:
> From: owner-vhdl-200x@eda.org [mailto:owner-vhdl-200x@eda.org] On Behalf Of whygee@f-cpu.org
>
>> Another question :
>> How do we define the size of a modular ?
>
> My feeling is it should be of a "universal integer".  And that we should extend the range of that type - but that's separate proposals:
>
> http://www.eda-twiki.org/cgi-bin/view.cgi/P1076/LongIntegers
> http://www.eda-twiki.org/cgi-bin/view.cgi/P1076/ArbitraryIntegers.
>
> Cheers,
> Martin
>

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