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Path: utzoo!watmath!clyde!cbosgd!gatech!seismo!umcp-cs!chris
From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.lang.c
Subject: Re: An amusing piece of code
Message-ID: <716@umcp-cs.UUCP>
Date: Sun, 6-Apr-86 01:39:26 EST
Article-I.D.: umcp-cs.716
Posted: Sun Apr  6 01:39:26 1986
Date-Received: Wed, 9-Apr-86 07:05:10 EST
References: <1370@ism780c.UUCP>
Reply-To: chris@maryland.UUCP (Chris Torek)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 76

In article <1370@ism780c.UUCP> tim@ism780c.UUCP (Tim Smith) writes:
>The situation is that we have something that, if written with if-then-else
>would be
>
>	if ( thing == A )
>		A-code;
>	else
>	if ( thing == B || thing == C || thing == D ) {
>		switch ( thing ) {
>	case B:         B-code; break;
>	case C:         C-code; break;
>	case D:         D-code; break;
>		}
>		BCD-common-code;
>	} else
>	if ( thing == E )
>		E-code;
>
>A, B, C, D, and E are constant expressions, so this is not elegant.
>We would like to use a switch for everything.

[followed by code using `if (0) {', which works, since case labels
are just that---*labels*---and are effectively `goto'ed.]

Beware!  Here is yet another opportunity for us `goto-ists' to come
out of the woodwork.  I include here an actual example from a piece
of my own code.  (I should probably change the gotos to be forward
references, rather than backward, though I am not certain it would
help.)

	/*
	 * Now that we have the parameter, perform the
	 * command.
	 */
	switch (DVI_DT(c)) {
	.
	.	[some material deleted]
	.

	case DT_DOWN:
move_down:
		dvi_v += p;
		/*
		 * `Vertical motion is done similarly, but
		 * with the threshold between ``small'' and
		 * ``large'' increased by a factor of 5.  The
		 * idea is to make fractions like $1\over2$
		 * round consistently, but to absorb
		 * accumulated rounding errors in the
		 * baseline-skip moves.'
		 */
		if (ABS(p) >= CurrentFont->vspace)
			vv = SPtoDEV(dvi_v);
		else {
			vv += SPtoDEV(p);
			p = SPtoDEV(dvi_v);
			FIXDRIFT(vv, p);
		}
		break;

	case DT_Y:
		dvi_y = p;
		goto move_down;

	case DT_Z:
		dvi_z = p;
		goto move_down;

	.
	.
	.
	}
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1415)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu