errata/282: Re: errata/282: signing

From: Shalom.Bresticker@motorola.com
Date: Fri Apr 30 2004 - 01:10:00 PDT

  • Next message: Alec Stanculescu: "errata/282: Re: errata/282: signing"

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

    From: Shalom.Bresticker@motorola.com
    To: Alec Stanculescu <alec@fintronic.com>
    Cc: harry@verplex.com, etf-bugs@boyd.com, btf-dtype@boyd.com
    Subject: Re: errata/282: signing
    Date: Fri, 30 Apr 2004 11:19:07 +0300 (IDT)

     Alec,
     
     Sorry, but you are mistaken on this.
     
     As previously discussed, the correct interpretation is (2).
     
     The word "expression" in 4.5.1 refers to the entire RHS.
     
     Also as previously discussed, the LRM is unfortunately not clear enough.
     
     There are some additional issues in the database related to signing,
     notably 35, 83, 96, 506.
     
     Shalom
     
     
     On Thu, 29 Apr 2004, Alec Stanculescu wrote:
     
    > Harry,
    >
    > You asked the following question which became issue 282:
    >
    > >Given the following Verilog 2001 case,
    > >
    > > module test(A,B,C,Z);
    > > parameter AW = 4, BW = 5, CW = 7, ZW = 10;
    > > input [AW-1:0] A; // 4 bits
    > > input [BW-1:0] B; // 5 bits
    > > input [CW-1:0] C; // 7 bits
    > > output [ZW-1:0] Z; // 10 bits
    > >
    > > assign Z = $signed(A) * $signed(B) + $unsigned(C);
    > > endmodule
    > >
    > >What we are trying to determine is which implementation of (1),
    > > (2) or (3) below is correct according to the standard rules defined in the
    > > LRM of Verilog 2001? >
    > > (1) Perform "D = $signed(A)*$signed(B)" first,
    > > then truncates it to C's size, denoted as value E,
    > > then the assignment "Z = $unsigned(E) + $unsigned(C)"
    > >
    > > (2) Perform "D = $unsigned(A)*$unsigned(B)" first,
    > > then the assignment "Z = $unsigned(D) + $unsigned(C)"
    > >
    > > (3) Perform "D = $signed(A)*$signed(B)" first,
    > > then the assignment "Z = $signed(D) + $unsigned(C)"
    > >
    >
    > In issue 282 the most relevant part of the LRM, which was omitted from
    > the discussion so far, is:
    >
    > "4.5.1 Expression type depends only on the operands. It does not depend
    > on the LHS. "
    >
    > Therefore, the first expression to evaluate is the
    > multiplication and the type of the expression depends only on the two
    > operands.
    >
    > Also, we should be happy that the LRM is very clear on this issue and
    > that the correct interpretation is consistent with sound language
    > design which leads the following two excerpts to be equivalent:
    >
    > "assign Z = $signed(A) * $signed(B) + $unsigned(C)"
    >
    > is equivalent to
    >
    > "assign D = $signed(A) * $signed(B);
    > assign Z = $signed(D) + $unsigned(B);
    > /* where D depends only on A and B as stipulated in 4.5.1*/"
    >
    > It would have been a nightmare if the LRM would have stated any
    > different on this issue.
    >
    > Regards,
    >
    > Alec Stanculescu
     
     --
     Shalom Bresticker Shalom.Bresticker @freescale.com
     Design & Reuse Methodology Tel: +972 9 9522268
     Freescale Semiconductor Israel, Ltd. Fax: +972 9 9522890
     POB 2208, Herzlia 46120, ISRAEL Cell: +972 50 5441478
     
     

    This archive was generated by hypermail 2.1.4 : Fri Apr 30 2004 - 01:10:17 PDT and
    sponsored by Boyd Technology, Inc.