Re: [sv-bc] RE: associativity of ** operator

VHDL has had the ** operator from day 1.  Associativity is not an issue because 
the grammar doesn't allow 2**3**4.  You have to parenthesize if there is more
than one ** operator in a sequence.  I've heard lots of complaints about VHDL,
but I've never heard anyone complain about the need for parentheses to write out
double exponentiation.

Paul
----- Original Message -----
From: "Shalom Bresticker" <shalom.bresticker@intel.com>
To: "Geoffrey.Coram" <geoffrey.coram@analog.com>, "Marq Kole" <marq.kole@nxp.com>
Cc: "Steven Sharp" <sharp@cadence.com>, "verilog-ams@eda.org" <verilog-ams@server.eda.org>, "sv-bc@eda.org" <sv-bc@server.eda.org>
Sent: Tuesday, October 27, 2009 7:22:02 AM
Subject: RE: [sv-bc] RE: associativity of ** operator

** was added in 1364-2001.

I don't have a record of associativity being discussed, but my records from that time are not complete.

Shalom
 

> -----Original Message-----
> From: Geoffrey.Coram [mailto:geoffrey.coram@analog.com] 
> Sent: Tuesday, October 27, 2009 1:05 PM
> To: Marq Kole
> Cc: Steven Sharp; verilog-ams@eda.org; Bresticker, Shalom; 
> sv-bc@eda.org
> Subject: Re: [sv-bc] RE: associativity of ** operator
> 
> Verilog-AMS had only the pow() operator -- where associativity was
> not an issue -- until LRM 2.3, where the ** operator was added,
> along with $math_functions ($exp, $sin), in accordance with Verilog.
> 
> When was ** added to 1364/1800?  Was associativity even considered?
> 
> -Geoffrey
> 
> 
> Marq Kole wrote:
> > Hi Steven, Shalom,
> > 
> > It's not a language incompatibility as Verilog-AMS also 
> uses left associativity for this operator. I brought it up 
> because of inconsistencies between the Verilog group of 
> language and other programming languages that support the 
> exponentiation operator, and the degeneration to single 
> exponentiation with a left associative exponentiation operator.
> > 
> > I'm quite sure that changing this will break very little 
> code, especially due to the degeneration - if you really 
> wanted exponentiation of exponentiation to happen you are 
> with the current standard forced to use parentheses.
> > 
> > Cheers,
> > Marq
> > 
> > 
> > Marq Kole
> > Product Manager AMSRF Simulation
> > NXP Semiconductors / Corporate I&T / Design Technology & Flows
> > 
> > -----Original Message-----
> > From: Steven Sharp [mailto:sharp@cadence.com] 
> > Sent: Tuesday 27 October 2009 7:19
> > To: Marq Kole; verilog-ams@eda.org; shalom.bresticker@intel.com
> > Cc: sv-bc@eda.org
> > Subject: Re: [sv-bc] RE: associativity of ** operator
> > 
> > 
> >> From: "Bresticker, Shalom" <shalom.bresticker@intel.com>
> > 
> >> I also don't see why you think that with left-to-right 
> associativity it becomes 
> > equivalent to * except for the left-most operator. If that 
> were the case, then 
> > 2**3**2 would give you (2**3)*2 = 16, not 64.
> > 
> > He means that (2**3)**2 is equivalent to 2**(3*2).  If you 
> left-associate
> > your exponentiation, you get the same result as multiplying 
> all of the
> > exponents and then exponentiating once.
> > 
> > I believe that other languages like FORTRAN right-associate 
> exponentiation,
> > and that one reason is that if you meant to left-associate, 
> you could have
> > just used multiplication.  That still takes one set of 
> parentheses, but
> > forcing right-association with a left-associative 
> convention takes a set
> > of parentheses for each exponent.  I might have brought 
> this up back when
> > exponentiation was added to Verilog.
> > 
> > 
> > 
> >> In these programming languages, it is a matter of definition.
> >>
> >> In any case, changing the associativity now would cause a 
> problem of backwards 
> > compatibility, which is the main reason it won't be changed 
> in SystemVerilog 
> > (There won't be any more 1364 as it has been merged into 
> SystemVerilog.).
> > 
> > 
> > Since Verilog-AMS probably took its conventions from SPICE, 
> which probably
> > took them from FORTRAN, it probably right-associates.  So 
> this would be
> > an incompatibility between the languages.
> > 
> > 
> > Steven Sharp
> > sharp@cadence.com
> > 
> > 
> 
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