errata/282: Re: errata/282: signing

From: Alec Stanculescu (alec@fintronic.com)
Date: Sun May 02 2004 - 21:50:00 PDT

  • Next message: Michael McNamara: "errata/282: Re: errata/282: signing"

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

    From: Alec Stanculescu <alec@fintronic.com>
    To: Shalom.Bresticker@motorola.com
    Cc: etf-bugs@boyd.com, btf-dtype@boyd.com
    Subject: Re: errata/282: signing
    Date: Sun, 2 May 2004 22:01:26 -0700

    > > The precedent providing the answer to this question is present in
    > > 4.1.5 Arithmetic operators (just a few paragraphs before the debated
    > > use of the word "expression").
    >
    > Alec,
    >
    > Are you confusing between 4.1.5 and 4.5.1 ?
    >
       The answer is NO. However, I do understand why you may be confused
       by 4.1.5 and 4.5.1. It is because in breaking with an important
       rule of how to write the LRM, writing the fix of errata 140 has
       introduced a forward reference in 4.1.5 to 4.5.1.
       
       Most forward references should be considered errata and
       eliminated. That would make for a much better LRM.
     
    > > 4.1.5 deals with the specific details of how the type of the
    > > expression is determined, and which states among other things
    > > that:
    > >
    > > "....
    > > The result of the power operator shall be real if either operand is a
    > > real, integer, or signed. If both operands are unsigned then the
    > > result shall be unsigned.
    > > ..."
    > >
    > > It is clear (because of the use of the word "both") that the type of
    > > the power-operator-expression depends only on the type of the operands
    > > of this particular operator and not on the operands present in a
    > > complex expression which may include the power operator as a
    > > subexpression. Also, I cannot imagine how it would be if the type of
    > > the power operator expression would depend on the operand on some
    > > other expression included in the same overall complex expression.
    >
    > You picked a bad example for several reasons.
    >
     The wordings of 4.1.5 in "version B" clearly showed the intention of
     the LRM to determine the type of the expression that uses the power
     operator as depending only on it's two operands.
     
     Given that this is one of the few places where the LRM showed it's intention
     one way or the other regarding whether "expression" in 4.5.1 means
     the entire ensemble of subexpressions, or just an expression having
     one operator, makes the "original wording of the LRM" extremely
     relevant. Basically, in fixing issue 140 the writer
     of the LRM has erased one instance of the clear intent of the LRM with
     respect to what "expression" means in 4.5.1. Also, the fix of errata 140,
     is flowed in that it introduced a forward reference in 4.1.5 to 4.5.1.
     Each forward reference in the LRM is basically an errata in itself!
     
    > One is that the text you quoted is from 1364-2001 Version B and is simply
    > incorrect. That was errata issue #140. The text was completely rewritten
    > and substantially changed.
    >
    > The second reason is that, yes, the type of the first operand of the power
    > operator (i.e., the base) is affected by the other operands in the
    > expression
    > in which it appears, i.e., it's bit-size and signedness.
    > (The second operand, the power, is self-determined, and not affected by other
    > operands.)
    >
    > Thirdly, the text refers only to the two operands of this operator in order to
    > not complicate the text further by talking about additional
    > operands.
     This is pure speculation and cannot be considered as argument.
     
    > Similarly, 4.1.7, for example, says that "When two operands of unequal bit
    > lengths are used ..., the smaller operand shall be zero filled ... to extend
    > to the size of the larger operand," and does not relate to other operands in
    > the larger expression. And the same is true of the other
    > subsections of 4.1.
     Thank you presenting the argument for me. Indeed several subsections
     in 4.1. describe the type of the expression in terms of the operands
     associated to the particular operator. This is so precisely because
     the type of an expression does not depend on the types of operands of
     other expressions that happen to be combined into the same complex
     expression with the one whose type we try to determine.
     
     As I stated earlier the size of the expression may also depend on
     context whereas the type of an expression depends only on the types of
     it's operands and not on it's context (i.e. on other sub-expressions
     combined in the same expression via the rules of precedence and via
     open and closed parenthesis).
     
    >
    > Shalom
    >
     Alec
     

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