From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,184737148aef02ac
X-Google-Attributes: gid103376,public
From: stt@houdini.camb.inmet.com (Tucker Taft)
Subject: Re: Fixed point multiplication ambiguity
Date: 1999/01/29
Message-ID: <F6AwFx.76y.0.-s@inmet.camb.inmet.com>#1/1
X-Deja-AN: 438182449
Sender: news@inmet.camb.inmet.com (USENET news)
X-Nntp-Posting-Host: houdini.camb.inmet.com
References: <78r4qh$fcu$1@plug.news.pipex.net>
Organization: Intermetrics, Inc.
Newsgroups: comp.lang.ada
Date: 1999-01-29T00:00:00+00:00
List-Id: <comp.lang.ada>

Nick Roberts (Nick.Roberts@dial.pipex.com) wrote:

: |... [ Integer(D*10.0 + 0.5) ] is effectively equivalent to:
: |   Integer(Duration(D*10.0)+Duration(0.5))


: I am not arguing with this, but which rule (or rules) in the RM specify the
: above interpretation, please? I've searched and searched (even the AI95s)!
: (Then again, I reckon my brain must be coming up for it's 20,000 mile
: service anyway ;-)

  RM95 3.4.1(6-7) introduces the universal numeric types.

  RM95 4.2(8) says that a real literal is of type universal-real.

  RM95 4.5.5(18) defines the multiplication operator:

    univ-fixed * univ-fixed => univ-fixed 

  RM95 8.6(21) indicates that any fixed-point type is acceptable
  when the expected type is universal-fixed, as is any universal
  type that "covers" universal-fixed (e.g. universal-real)
  (i.e., any fixed-point type is implicitly convertible to
  universal-fixed, as is universal-real).

  RM95 8.6(24) indicates that universal fixed is acceptable
  when the expected type is any specific fixed-point type 
  (i.e., universal fixed is implicitly convertible to any
  fixed-point type).

  RM95 8.6(28) indicates that if there is exactly one acceptable
  interpretation for a complete context, then that one is chosen.

There is only one directly visible "*" operator which can "accept"
one operand of type Duration (D), and one univeral-real operand (10.0):
univ-fixed * univ-fixed => univ-fixed.

There is also only one directly visible "+" operator which can "accept"
one universal-fixed operand (D*10.0) and one universal-real operand
(the literal 0.5): Duration + Duration => Duration.

Hence, the only acceptable interpretation is the one which
is effectively equivalent to: 

    Integer(Duration(D*10.0) + Duration(0.5))

Q.E.D. (I hope ;-).

: -------------------------------------------
: Nick Roberts
: -------------------------------------------

--
-Tucker Taft   stt@averstar.com   http://www.averstar.com/~stt/
Technical Director, Distributed IT Solutions  (www.averstar.com/tools)
AverStar (formerly Intermetrics, Inc.)   Burlington, MA  USA