Re: errata/282: signing version=2.63

From: Shalom.Bresticker@freescale.com
Date: Tue May 04 2004 - 12:00:00 PDT

  • Next message: Bruce LaVigne: "Re: errata/282: signing version=2.63"

    The following reply was made to PR errata/282; it has been noted by GNATS.

    From: Shalom.Bresticker@freescale.com
    To: Alec Stanculescu <alec@fintronic.com>
    Cc: etf-bugs@boyd.com
    Subject: Re: errata/282: signing
    Date: Tue, 4 May 2004 22:11:24 +0300 (IDT)

     Alec,
     
    > I agree with everything you said, with the possible exception that you
    > appear to be of the opinion that the writing of the LRM was
    > successful in making "sign rules follow vector width rules". This is
    > not the case because sign rules change the sign of operands (from what
    > they were specified by the user!) whereas vector width rules do not
    > affect what the user wrote, they do not change the width of any
    > operand. They just describe what happens to the result.
     
     This is not so.
     Consider this case:
     
     a is 8 bits, b is 4 bits, b = 4'b1100
     
     If I write
     
     a = ~b;
     
     then b is first widened to 8 bits, giving me 8'b00001100.
     When I complement it, I get a = 8'b11110011.
     
     Whereas if I first complemented b, then widened the result,
     I would get 8'b00000011.
     
     Shalom
     

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