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