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

 
-----Non-member submission-----
From: Will Adams [mailto:wadams@freescale.com] 
Sent: Friday, July 28, 2006 9:02 AM

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.
>