Path: utzoo!mnetor!uunet!husc6!mailrus!nrl-cmf!ames!ubvax!weitek!mahar From: mahar@weitek.UUCP (Mike Mahar) Newsgroups: comp.arch Subject: Re: negative addresses Message-ID: <389@attila.weitek.UUCP> Date: 10 May 88 16:37:55 GMT References: <2393@uvacs.CS.VIRGINIA.EDU> Reply-To: mahar@attila.UUCP (Mike Mahar) Organization: WEITEK Corporation, Sunnyvale, CA Lines: 22 In article <2393@uvacs.CS.VIRGINIA.EDU> wulf@uvacs.CS.VIRGINIA.EDU (Bill Wulf) writes: >Has anyone ever seen a machine with "negative addresses", that is, one >where the address space is -2**31..2**31-1 rather than 0..2*32-1?? >Any thoughts on what the problems with such a scheme might be (or are)? > >Why ask such a question, you ask -- well, I'm trying to remove unsigned >arithmetic from WM, and as far as I can tell, the primary (only?) use >of unsigned arithmetic is for address computations. Soooooo... > >Bill Wulf A pretty good arguement can be made that the 68000 is a signed address machine. And the address displacements are signed. There is even a short absolute addressing mode. It uses an absolute 16-bit signed address. Most compilers only use 32K of that address because they want memory to start at 0. The addressing modes of the 68000 are more orthognal if you assume that address 0 is the middle of memory rather than the beginning. -- Mike Mahar UUCP: {turtlevax, cae780}!weitek!mahar