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Path: utzoo!mnetor!seismo!rutgers!mit-eddie!uw-beaver!ubc-vision!ubc-cs!manis
From: manis@ubc-cs.UUCP (Vincent Manis)
Newsgroups: comp.lang.c
Subject: Re: + != + (floating point)
Message-ID: <1285@ubc-cs.UUCP>
Date: Thu, 23-Apr-87 12:22:14 EST
Article-I.D.: ubc-cs.1285
Posted: Thu Apr 23 12:22:14 1987
Date-Received: Sat, 25-Apr-87 14:57:37 EST
References: <133@starfire.UUCP>
Reply-To: manis@ubc-cs.UUCP (Vincent Manis)
Organization: UBC Department of Computer Science
Lines: 32

In article <133@starfire.UUCP> merlyn@starfire.UUCP (Brian Westley) writes:
>Integer addition is communative [sic] & associative.  Floating addition is
>communative, but NOT associative.
>Merlyn Leroy ..rutgers!dayton!rosevax!rose3!starfire!merlyn

This statement is flat-out wrong. On a machine with 16-bit ints 

   32767 + (-2) + 1

and 

   32767 + 1 + (-2)

may lead to different results. It so happens that both will "work" on some
machines with 2's complement, but 2's complement is only mandated by the
Draft Standard (according to Harbison and Steele) for unsigned, not signed,
ints. Even on some 2's complement machines, such as the IBM 370, there are
modes in which the second expression will cause a fault (though fixed
overflow checking is generally disabled).

-----
Vincent Manis                {seismo,uw-beaver}!ubc-vision!ubc-cs!manis
Dept. of Computer Science    manis@cs.ubc.cdn
Univ. of British Columbia    manis%ubc.csnet@csnet-relay.arpa  
Vancouver, B.C. V6T 1W5      manis@ubc.csnet
(604) 228-6770 or 228-3061

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