RE: [vhdl-200x] Logical (and shift) operations on Integers

Hi Martin,

 

Yes, that is what I mean as regards representation and error condition.

 

Thank you for clarifying my email.

 

Regards,

 

Peter.

 

 

From: owner-vhdl-200x@eda.org [mailto:owner-vhdl-200x@eda.org] On Behalf Of
Martin.J Thompson
Sent: 29 August 2014 13:00
To: vhdl-200x@eda.org
Subject: RE: [vhdl-200x] Logical (and shift) operations on Integers

 

Thanks Peter, 

 

Can I clarify -  by "be represented by integers of those values" I assume
you mean the 157 would be represented by the normal 2-s complement bit
pattern for "157" at all times, even when part of a constrained subtype as
in the example?

 

Presumably the shift wouldn't produce an out-of-range error if the result of
the shift was being assigned to a suitably ranged (or unconstrained range)
integer?

 

Thanks,

Martin

 

 

From: owner-vhdl-200x@eda.org [mailto:owner-vhdl-200x@eda.org] On Behalf Of
Peter Flake
Sent: 29 August 2014 12:34
To: vhdl-200x@eda.org
Subject: RE: [vhdl-200x] Logical (and shift) operations on Integers

 

Hi Martin,

 

I would allow logical and shift operators on all integers and subtypes of
integers.  A subtype with range 157 to 160 would be represented by integers
of those values.  Applying a shift should therefore produce an out-of range
error!

 

Regards,

 

Peter

 

 

From: owner-vhdl-200x@eda.org [mailto:owner-vhdl-200x@eda.org] On Behalf Of
Martin.J Thompson
Sent: 29 August 2014 11:20
To: vhdl-200x@eda.org
Subject: [vhdl-200x] Logical (and shift) operations on Integers

 

Hi all,

 

There was some discussion on yesterday's telecon of allowing logical
operations on integers.  There is also quite a lot of previous discussion
here:

 

http://www.eda-twiki.org/cgi-bin/view.cgi/P1076/IntegerOperators

 

Shift operators could also be considered.

 

One of the implications of doing this is that it would define a definite
representation for integers which have these operations applied to them (ie
2-s complement binary).

 

So in terms of gathering requirements, what would people like to use these
operators for?  Some examples which occur to me off the top of my head:

.         Masking bits

.         Shift registers (should simulate faster than vectors, but whether
this is significant I don't know!)

.         Xoring in crc generators

.         What else?

 

Things it probably shouldn't be used for (in future) could be:

.         Power-of-2 Wraparound counters - we'll have modular types for this

.         Others?

 

 

Is this a proposal worth further consideration or not?  I see three options
at this stage, but am of course open to others!

 

.         Don't allow it, it's too constraining on the implementation - use
a modular type if you want bit operations.

.         Allow it, but only on integers which have a range covering a 'full
power-of-2'

.         Allow it on all integer ranges - in which case how to treat things
like integers ranged 157 to 160 - should the compiler normalise that to 0 to
3 for logical and shifting purposes or treat them as effectively full-width
2s complement vectors

 

Thanks,

Martin

 

 

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Martin Thompson BEng(Hons) MIET CEng

martin.j.thompson@trw.com  +44 121 627 3569  

TRW Conekt, Stratford Road, Solihull, B90 4GW

http://www.conekt.co.uk/

 

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