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From: brooks@lll-crg.UUCP
Newsgroups: net.lang.c
Subject: Re: Compiler Specific Operators
Message-ID: <3519@lll-crg.ARpA>
Date: Sat, 12-Jul-86 20:03:20 EDT
Article-I.D.: lll-crg.3519
Posted: Sat Jul 12 20:03:20 1986
Date-Received: Sat, 12-Jul-86 23:19:50 EDT
References: <1825@uw-beaver> <5780@alice.uUCp>
Reply-To: brooks@lll-crg.UUCP (Eugene D. Brooks III)
Organization: CRG, Lawrence Livermore Labs
Lines: 24

>C already has a hook for such things.  It's called the "asm" statement.
>Despite its name, there is no law that says that what follows "asm"
>must in fact be assembly language.  If you're writing the compiler,
>you can implement whatever syntax you like with whatever semantics you like.
It would be nice if asm was more "printf like" instead of just dumping
a string.  I have made quite a lot of use of asms when writing things like
multitasking packages and other things which need assembler hooks.  Most
of the code can be in C and be reasonably portable.  I have often needed
the ability to stick a stack address in an asm without knowing just what
stack address you want to load...

ie

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.