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From: cottrell@NBS-VMS.ARPA (COTTRELL, JAMES)
Newsgroups: net.lang.c
Subject: What happened to labels
Message-ID: <1420@brl-smoke.ARPA>
Date: Fri, 28-Feb-86 19:12:13 EST
Article-I.D.: brl-smok.1420
Posted: Fri Feb 28 19:12:13 1986
Date-Received: Mon, 3-Mar-86 00:35:55 EST
Sender: news@brl-smoke.ARPA
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/*
> I recall that C on early UNIX's treated labels as constants of type
> (int *).  As a result, you could assign labels to variables and even
> jump to the label in a variable.  This got taken out of K&R, and
> as I far as I can tell it's not in other C's today.
> 
> This is unfortunate; 

I don't think you will get much sympathy on this point.

> I ran into a situation recently in which I wanted
> to (automatically) generate C code that should, for efficiency reasons,
> contain label variables.  I had to simulate them with a switch statement
> of the form:
> 
> 	switch(labelindex) {
> 		case 1: goto label1;
> 		case 2: goto label2;
> 		...
> 		case n: goto labeln;
> 		default: fprintf(stderr,"unknown label index: %d\n",
> 					labelindex);
> 			 abort();
> 	}

 	switch(labelindex) {
 		case 1: label1: <code> break;
 		case 2: label2: <code> break;
 		...
 		case n: labeln:	<code> break;
 		default: fprintf(stderr,"unknown label index: %d\n",
 					labelindex);
 			 abort();
 	}

 
> This is a lot slower, though, and some of the compiler's I tried it
> on (the VAX VMS C compiler, for example) did not peephole optimize the
> jump table implementing the switch and the branch instructions
> implementing the goto's (this should have been treated as a jump
> to a jump).
> 
> I'm curious if any commerically available C compilers implement jumps
> to arbitrary pointers without recourse to assembly language inserts.

Probably not. I think they all wised up. Why don't you?

	jim		cottrell@nbs
*/
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