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Path: utzoo!linus!decvax!harpo!seismo!rlgvax!guy
From: guy@rlgvax.UUCP (Guy Harris)
Newsgroups: net.rumor
Subject: Re: New Vaxen info
Message-ID: <1340@rlgvax.UUCP>
Date: Wed, 26-Oct-83 20:02:42 EDT
Article-I.D.: rlgvax.1340
Posted: Wed Oct 26 20:02:42 1983
Date-Received: Thu, 27-Oct-83 20:49:06 EDT
References: <178@rna.UUCP>
Organization: CCI Office Systems Group, Reston, VA
Lines: 27


		- implements a proper subset of the VAX instruction set,
	missing PDP-11 compatibility mode, decimal arithmetic, certain string,
	D and H floating point and a few other instructions. The string move
	instructions MOVC3/5 are implemented. ... can anyone comment on the
	effect of these missing instructions on the porting of UNIX to the
	MicroVAX I ? (DEC will provide it as MicroVAX ULTRIX).

The VAX-11 PCC doesn't generate PDP-11 instructions (obviously), decimal
arithmetic, or H floating point.  It uses D floating point because of
the way C does floating point calculations (everything in double precision).
(That was *D* and H?  I would have suspected G and H, myself, as I don't
know whether DEC Fortran can be told not to generate any double-precision
instructions, and because I suspect D and F floating point share more than
F and G do.)  It does generate movc instructions for structure copies/calls/
returns.

Furthermore, the kernel does make use of a number of other string instructions
which are either in the assembly language support or are put in there by
"sed" scripts massaging compiled C code.  I suspect that there may not be
too many problems, as VMS probably also uses a lot of those instructions.
The subset was probably designed around VMS and those VMS programs they
expected to run on the MicroVAX.  Then again, they could all be #ifdefed
out if the kernel was built to support a MicroVAX.

	Guy Harris
	{seismo,mcnc,brl-bmd,allegra}!rlgvax!guy