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- Newsgroups: comp.arch
- Path: sparky!uunet!stanford.edu!CSD-NewsHost.Stanford.EDU!SAIL.Stanford.EDU!andy
- From: andy@SAIL.Stanford.EDU (Andy Freeman)
- Subject: Re: Any use for Branch if Even/Odd ?
- Message-ID: <1992Dec15.183127.3025@CSD-NewsHost.Stanford.EDU>
- Sender: news@CSD-NewsHost.Stanford.EDU
- Organization: Computer Science Department, Stanford University.
- References: <id.08RV.WYB@ferranti.com> <1992Dec14.203631.16388@CSD-NewsHost.Stanford.EDU> <1992Dec15.024545.7336@ryn.mro4.dec.com>
- Date: Tue, 15 Dec 1992 18:31:27 GMT
- Lines: 23
-
- In article <1992Dec15.024545.7336@ryn.mro4.dec.com> Peter.Mayne@cao.mts.dec.com writes:
- >In article <1992Dec14.203631.16388@CSD-NewsHost.Stanford.EDU>, andy@SAIL.Stanford.EDU (Andy Freeman) writes:
- >>Does anyone know why they preferred even/odd to >=0/<0? Sometimes one
- >>has to test the sign bit, so why not use it whenever one can use any
- >>bit to split things into two classes?
- >
- >VMS status codes record more than just true/false. The bottom three bits of
- >a status code are encoded as follows:
-
- So? Any three bits work just as well.
-
- >Opinion: If the status codes were at the high end of the longword, the
- >error codes for a particular facility would be scattered all over the
- >range instead of in a single group of numbers; harder for us humans to
- >comprehend. Given that the VAX architecture has bit test operations,
- >why not do it this way?
-
- DEC's dinosaurs had symbolic assemblers and debuggers. I "remember"
- that even some of the 11's had similar software well before the vax
- and VMS was invented.
-
- -andy
- --
-