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From: thorinn@diku.UUCP (Lars Henrik Mathiesen)
Newsgroups: net.lang.c
Subject: Re: mildly (sic) obfuscating c (really style)
Message-ID: <21@diku.UUCP>
Date: Fri, 20-Dec-85 21:04:30 EST
Article-I.D.: diku.21
Posted: Fri Dec 20 21:04:30 1985
Date-Received: Sun, 22-Dec-85 00:52:25 EST
References: <564@puff.UUCP> <979@rlvd.UUCP>
Distribution: net
Organization: DIKU, U of Copenhagen, DK
Lines: 43

In article <564@puff.UUCP> tom@puff.UUCP writes:
[describes code using a label as a function address,
 and the various results on different machines]

  Well, ON A VAX, all you have to do is to put in the register save
mask (well, it was you who started doing assemblerish things in C :-).

-------------------------------------------------------
main() {
	register thing = 0;

	if (0) {			/* skip mask on first entry */
stuff:		;
		asm(".word	0x800");	/* save r11 (thing) */
		;
	}
	printf("Here it goes, thing is %d\n", thing);
	if (!thing++)
		(*(int(*)())stuff)();
	printf("There it went (one), thing is %d\n", thing);
	printf("There it went (two), thing is still %d\n", thing);
}
-------------------------------------------------------

  The results are relatively unsurprising:

-------------------------------------------------------
Here it goes, thing is 0
Here it goes, thing is 1
There it went (one), thing is 2
There it went (two), thing is still 2
There it went (one), thing is 1
There it went (two), thing is still 1
-------------------------------------------------------

  Remarks: R11 is saved at label stuff because that's what C does at
entry to main; if you don't save it, the two last lines read 2 instead.
Don't use cc -O, as this gets you an undefined label in `as'.

  Maybe this shows that the conceptual model behind C looks like a VAX;
but then maybe we knew that already.
--
Lars Mathiesen, DIKU, Copenhagen, Denmark	..!mcvax!diku!thorinn