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From: maa@nbires.nbi.com (Mark Armbrust)
Newsgroups: comp.arch,comp.lang.misc
Subject: Re: Language Tenets (was Re: Double Width Integer Multiplication and Division
Message-ID: <424@nbires.nbi.com>
Date: 13 Jul 89 16:02:37 GMT
References: <57125@linus.UUCP> <1989Jun24.230056.27774@utzoo.uucp> <13946@haddock.ima.isc.com> <1388@l.cc.purdue.edu> <13961@haddock.ima.isc.com> <147@ssp1.idca.tds.philips.nl> <1207@quintus.UUCP>
Reply-To: maa@nbires.UUCP (Mark Armbrust)
Organization: NBI Inc, Boulder CO
Lines: 54

In article <1207@quintus.UUCP> pds@quintus.UUCP (Peter Schachte) writes:
>In article <147@ssp1.idca.tds.philips.nl> roelof@idca.tds.PHILIPS.nl (R. Vuurboom) writes:
>>In article <13961@haddock.ima.isc.com> suitti@haddock.ima.isc.com (Stephen Uitti) writes:
>>>Is there anything really evil with this:
>>>	q = divrem(top, bottom, &remainder);
>>Well, since you ask...yes.
>>A basic language architectural tenet is that logical (semantic) grouping 
>>should lead to syntactic grouping and vice verse. Any of the notations below 
>>would satisfy this
>>	q r  <- t/b
>[followed with variations on this basic style]
>
	. . .
>
>All is not lost, though.  In C, you can have
>
>	divrem(top, bottom, &quotient, &remainder)

How about:

typedef struct _divResult {
	int	q;
	int	r;
	}	divResult;

extern divResult divide (int, int);

main() {
	divResult	qr;
	int		i, j;
	. . .
	qr = divide (i, j);	/* qr.q is quotient, qr.r is remainder */
	. . .
	}

If the compiler can't do a good enough job on divide(), it is trivial to
write in assembly language.

In the case of MSC 5.1, the return values from divide() are in registers, so
there is very little overhead using this method.

divide:	push	bp
	mov	bp, sp
	mov	ax, [bp+4]
	cwd
	idiv	word ptr [bp+6]
	pop	bp
	ret		; qr.q returned in ax, qr.r in dx

-- 

Mark Armbrust
maa@nbires.nbi.com
maa@nbires.UUCP