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From: robert@cheviot.newcastle.ac.uk (Robert Stroud)
Newsgroups: net.lang.c
Subject: Re: Compiler Specific Operators
Message-ID: <889@cheviot.newcastle.ac.uk>
Date: Tue, 15-Jul-86 10:22:07 EDT
Article-I.D.: cheviot.889
Posted: Tue Jul 15 10:22:07 1986
Date-Received: Thu, 24-Jul-86 00:29:02 EDT
References: <1825@uw-beaver> <5780@alice.uUCp> <3519@lll-crg.ARpA>
Reply-To: robert@cheviot.ncl.ac.uk (Robert Stroud)
Organization: Computing Laboratory, University of Newcastle upon Tyne, UK
Lines: 37

In article <3519@lll-crg.ARpA> brooks@lll-crg.UUCP (Eugene D. Brooks III) writes:
>It would be nice if asm was more "printf like" instead of just dumping
>a string.

>suppose you want to change the stack pointer...
>
>	char *oldpointer;
>	char *newpointer;
>
>	asm("store sp,%a", oldpointer);
>	asm("load sp,%a", newpointer);
>
>The code is machine dependent, but the compiler takes care of the
>C name -> AS name  mapping for you.   Of course I guess the compiler
>should not encourage such screwing around.

A machine called the Orion made by a British company called High Level
Hardware has something similar. It is based on a bit slice architecture
and has been microcoded as a stack based C machine. Consequently, it is
possible to interpret

	asm(opcode, expr, ...)

as "push all the C expressions onto the stack and then perform opcode".

This lets you mix C expressions with special-purpose opcodes (you can
define your own because the microcode is user-extensible). However,
the clean semantics are only possible because it is a stack machine
and all operations are performed in this way.

Robert Stroud,
Computing Laboratory,
University of Newcastle upon Tyne.

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