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=-1.4 required=5.0 tests=BAYES_00,FREEMAIL_FROM, SUBJ_ALL_CAPS autolearn=no autolearn_force=no version=3.4.4 X-Google-Thread: 103376,c4cb2c432feebd9d X-Google-Thread: 1094ba,c4cb2c432feebd9d X-Google-Thread: 101deb,15c6ed4b761968e6 X-Google-Attributes: gid103376,gid1094ba,gid101deb,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news2.google.com!news1.google.com!news4.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!wn14feed!worldnet.att.net!bgtnsc05-news.ops.worldnet.att.net.POSTED!b680011b!not-for-mail From: Dick Hendrickson User-Agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.lang.ada,comp.lang.fortran,comp.lang.pl1 Subject: Re: ONES COMPLEMENT References: <0ugu4e.4i7.ln@hunter.axlog.fr> <%P_cg.155733$eR6.26337@bgtnsc04-news.ops.worldnet.att.net> <6H9dg.10258$S7.9150@news-server.bigpond.net.au> <1hfv5wb.1x4ab1tbdzk7eN%nospam@see.signature> <20060712.7A4E6E0.D028@mojaveg.lsan.sisna <20060717.7A4ADD0.10B1A@mojaveg.lsan.sisna.com> <44bceab6$29$fuzhry+tra$mr2ice@news.patriot.net> <20060719.79A3E90.87CE@mojaveg.lsan.sisna.com> <44be98a1$38$fuzhry+tra$mr2ice@news.patriot.net> <20060720.79BD230.8698@mojaveg.lsan.sisna.com> <44c00809$1$fuzhry+tra$mr2ice@news.patriot.net> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Message-ID: NNTP-Posting-Host: 2692fc15f358d0450ab26bd0ee29843b X-Complaints-To: abuse@worldnet.att.net X-Trace: bgtnsc05-news.ops.worldnet.att.net 1153515618 2692fc15f358d0450ab26bd0ee29843b (Fri, 21 Jul 2006 21:00:18 GMT) NNTP-Posting-Date: Fri, 21 Jul 2006 21:00:18 GMT Organization: AT&T Worldnet Date: Fri, 21 Jul 2006 21:00:18 GMT Xref: g2news2.google.com comp.lang.ada:5869 comp.lang.fortran:12319 comp.lang.pl1:2084 Date: 2006-07-21T21:00:18+00:00 List-Id: glen herrmannsfeldt wrote: > Shmuel (Seymour J.) Metz wrote: > (snip) > >> Robin wrote "A properly designed 1s complement machine would not >> generate -0 in normal arithmetic operations." > > >> I responded "0+(-0)?". > > >> You responded "A subtractive adder." > > >> I'm trying to say that there's nothing about 0+(-0) requiring a >> subtractive adder. > > > Well, even more, the way I understand the logic of some machines, > as long as no arguments are negative zero they won't generate a > negative zero. 0+(-0) doesn't satisfy that case. > > For those who care, consider that ones complement arithmetic > will normally generate -0 instead of +0. Adding x and -x generates > all ones with no end around carry. If you add the ones complements > of the two operands you get the complement of the result, and still > negative zero for zero sum. The complement of that will be the correct > sum, and won't be negative zero unless both of the arguments are -0. It's been a long time, but my recollection is that the CDC machines used a subtractor rather than an adder. This was done to mostly eliminate the -0 problem. Rather than do X + Y, they did X - (-Y). Then, if Y happened to be -X the subtractor saw X + (-X) as X - (--X) which worked out to X - X and then to zero. I think the only problem was 0 + 0 which became 0 - (-0) and then -0 . > > In addition, note that ECL supplies a signal and its complement without > any extra logic needed. Maybe, but the CDC 1604s used discrete parts. Transistors, resistors, on a 3 inch by 3 inch circuit board. I'm pretty sure that some design decisions were heavily influenced by parts count. > > In any case, a high level language has to get it right even > if it takes extra instructions. Absolutely. Dick Hendrickson > > -- glen >