Re: errata/344: Case Statements with Real Expressions

From: Michael McNamara (mac@verisity.com)
Date: Fri May 09 2003 - 14:10:08 PDT

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    The following reply was made to PR errata/344; it has been noted by GNATS.

    From: Michael McNamara <mac@verisity.com>
    To: Steven Sharp <sharp@cadence.com>
    Cc: etf-bugs@boyd.com, mac@verisity.com
    Subject: Re: errata/344: Case Statements with Real Expressions
    Date: Fri, 9 May 2003 14:05:43 -0700

     Steven Sharp writes:
    >
    > > Hence my rather tenuous logic takes 4.5.1, with 4.1.8 implying that
    > > case is the same as '===', and 4.5.2 to say that we should coerce the
    > > argumenmts to === and !=== to unsigned, absent other statements (note
    > > that other statements do exist specifing the type coercion for the <,
    > > >, <= and >= operators, in section 4.1.7)
    >
    > This argument is invalid. The fact that the result of the compare is
    > an unsigned value does not imply that the inputs are coerced to unsigned,
    > any more than the fact that the result of the compare is 1 bit wide
    > implies that the inputs are coerced to 1 bit wide before the compare.
    >
    > Note that the result of '==' is also 1 bit unsigned, but it can still
    > be used to perform compares between real values, which do not get
    > converted to unsigned integers before the compare.
    >
    > Steven Sharp
    > sharp@cadence.com
     
     Don't get me wrong -- I know the right answer -- it is just that the
     standard is silent on whether reals can be used in case statements,
     and there is ambiguous language in various places that _might_ lead
     you down various paths.

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