RE: [sv-bc] [Fwd: Issues with IEEE 1364-2005]

While that is correct in principle, what we really want to say is
something more easily understandable, along the lines of "If the
condition is false (equal to 0)", similar to the original language,
while still being accurate.

"logical inequality comparison of expression1 with zero" is correct, but
takes time to figure out what it actually does, and is liable to be
misread, as shown by the fact that we made a mistake when formulating it
and no one found the mistake till now.

Shalom

> -----Original Message-----
> From: Will Adams [mailto:wadams@freescale.com]
> Sent: Friday, July 28, 2006 7:02 PM
> To: Bresticker, Shalom
> Cc: Brad Pierce; sv-bc@eda-stds.org; michael.burns@freescale.com
> Subject: Re: [sv-bc] [Fwd: Issues with IEEE 1364-2005]
> 
> It seems the fix for the definition of the conditional operator is to
> replace `logical equality comparison of expression1 with zero' with
> `logical inequality comparison of expression1 with zero'.
> 
> will
> 
> 
> Bresticker, Shalom wrote:
> > Note that in 1364-2001, the description of ?: was not reversed. It
was
> > ambiguous, but not reversed. For a description of how and why it was
> > changed, see http://boyd.com/1364_btf/report/full_pr/403.html .
> >
> > Shalom
> >
> >
> >> I do agree that the description of the condition evaluation in
5.1.13
> >> appears to be reversed.
> >>
> >>> On the evaluation of the conditional operator, IEEE 1364-2005,
> > section
> >>> 5.1.13 `Conditional operator', states the following.
> >>>
> >>>    conditional_expression ::= (From A.8.3)
> >>>      expression1 ? { attribute_instance } expression2 :
expression3
> >>>    expression1 ::= expression
> >>>    expression2 ::= expression
> >>>    expression3 ::= expression
> >>>
> >>>    The evaluation of a conditional operator shall begin with a
> > logical
> >>>    equality comparison (see 5.1.8) of expression1 with zero,
termed
> >> the
> >>>    condition. If the condition evaluates to false (0), then
> >> expression3
> >>>    shall be evaluated and used as the result of the conditional
> >>>    expression. If the condition evaluates to true (1), then
> >> expression2
> >>>    is evaluated and used as the result. If the condition evaluates
> > to
> >> an
> >>>    ambiguous value (x or z), then both expression2 and expression3
> >> shall
> >>>    be evaluated; and their results shall be combined, bit by bit,
> >> using
> >>>    Table 5-21 to calculate the final result unless expression2 or
> >>>    expression3 is real, in which case the result shall be 0.
> >>>
> >>> I am not sure why this defines `condition' as `a logical equality
> >>> comparison of expression1 with zero', since this means that
> >> `condition'
> >>> is the negation of `expression1' (`expression1 == 0' is 1 when
> >>> `expression1' is 0, 0 when it is 1, and X when it is X or Z), and,
> >>> applying the rest of the definition, when `expression1' is 1,
> >>> `condition' is 0, and so `expression3' is evaluated as the result
of
> >> the
> >>> conditional expression. Similarly, if `expression1' is 0, then
> >>> `expression2' is evaluated as the result of the conditional
> >> expression.
> >>> This seems to give the semantics of an `if else then' operator,
> > rather
> >>> than an `if then else', which I doubt is what is intended.
> >