RE: [sv-bc] RE: [sv-ac] Mantis 1974: Definitions of true and false conditions

Hi, Tom.


________________________________

	From: owner-sv-bc@server.eda.org
[mailto:owner-sv-bc@server.eda.org] On Behalf Of Alsop, Thomas R
	Sent: Wednesday, August 15, 2007 8:36 PM
	To: Brad Pierce; sv-bc
	Cc: sv-ac@server.eda-stds.org
	Subject: RE: [sv-bc] RE: [sv-ac] Mantis 1974: Definitions of
true and false conditions
	
	

	Brad, It isn't clear if you are agreeing with Shalom on this or
not.  

	 

	I don't think 12.4 and 16.3 fall into the same category as the
ternary "?:" operator. With the ternary operator we have a clear
assignment into the first argument and the result is coming from one of
two expressions which will evaluate to a scalar/singular type.  Table
11-22 is very clear on how we remove some of the x propagation pessimism
when we do the bit by bit comparison.  

	 

	In 12.4 the "If then Else" semantics do not necessarily result
in the assignment of a single scalar type, but can be multiple
assignments to different objects.  In 16.3, the assertion "selector
expression" is typically going to print a message and is not going to do
any type of bit by bit concatenation operation.  Hence, I don't believe
there is any need to change their current wording or semantics.

	 

	[SB] As I have explained, that is not the issue I brought up in
1974. 
	

	I also want to comment on a question I am seeing near Table
11-22

	 

	QUESTION:

	Is the shorter

	operand always

	zero extended, or

	can it be sign

	extended? 

	 

	It's referring to this sentence "If the lengths of the first and
second expression are different, the shorter operand shall be

	lengthened to match the longer and zero-filled from the left
(the high-order end)."

	 

	I think this should be sign extended.  It will most closely
match real implementation.  Also it matches our sign extension rules

	 

	From 10.7:

	When the right-hand side evaluates to fewer bits than the
left-hand side, the right-hand side value is

	padded to the size of the left-hand side. If the right-hand side
is unsigned, it is padded according to

	the rules specified in 11.6.1. If the right-hand side is signed,
it is sign-extended.
	[SB] That particular paragraph is not completely relevant, as it
describes assignment rules, and here it is not an assignment. However,
Mantis 1004 resolved this to change the sentence to: 

	The first and second expressions are extended to the same width,
as described in 11.6.1 and 11.7.2.

	 

	Shalom

	
	


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