Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!zaphod.mps.ohio-state.edu!ncar!asuvax!stjhmc!p88.f15.n300.z1.fidonet.org!Lawson.English From: Lawson.English@p88.f15.n300.z1.fidonet.org (Lawson English) Newsgroups: comp.sys.mac.programmer Subject: Re: 68000 Assembly question -- overflow Message-ID: <12977.2847A793@stjhmc.fidonet.org> Date: 1 Jun 91 13:49:10 GMT Sender: ufgate@stjhmc.fidonet.org (newsout1.26) Organization: FidoNet node 1:300/15.88 - Tucson Apple Core, Tucson AZ Lines: 35 Seth Tisue writes in a message to All ST> I wasn't advocating one's complement arithmetic -- I'm not that ST> naive. What I was wondering was, why not have $80000000 (-2^31) ST> be an invalid number rather than -2^31, thus removing the asymmetry? ST> I'm assuming there's some good reason for this... What uses does ST> one "often have" for the extra number? Why would you want to eliminate a number from the range? It exists as a natural consequence of 2's compliment arithmatic. To specify that -2^31 didn't really exist would take computer languages another step away from the machine without reason, and require that compiler writers write exception code so that that number would be invalid, even though it existed at the hardware level. As for whether "one often has" a use for the extra number, nah... I was being silly. But the added complexity that eliminating -2^ would add to a language implementation would be rediculous: imagine having to do a range check as well as an over-flow check whenever you added or subtracted a number... Sloooow. Someone else has suggested that we drop this. Let's take it to E-mail after this if we continue. Lawson -- Uucp: ...{gatech,ames,rutgers}!ncar!asuvax!stjhmc!300!15.88!Lawson.English Internet: Lawson.English@p88.f15.n300.z1.fidonet.org