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From: tainter@ihlpg.UUCP (Tainter)
Newsgroups: net.lang.c
Subject: Re: generalized switch
Message-ID: <2299@ihlpg.UUCP>
Date: Mon, 4-Aug-86 18:18:00 EDT
Article-I.D.: ihlpg.2299
Posted: Mon Aug  4 18:18:00 1986
Date-Received: Tue, 5-Aug-86 06:05:55 EDT
References: <15093@ucbvax.BERKELEY.EDU> <2765@brl-smoke.ARPA> <15120@ucbvax.BERKELEY.EDU>
Organization: AT&T Bell Laboratories
Lines: 44

> Sure, that's the way I have been doing it. But you can do that with
> any choice among cases.
> As I understand it, a switch/case setup compiles exactly the same as
> 	if (var == const1) {.....};
> 	else if (var == const2) {.....};
> 	else  {default_action};
> anyway. (Or am i wrong?). In any case, it can be rewritten that way.
> Joshua Kosman
> kos@ernie.berkeley.EDU

You are wrong.
switch (a) {
    case 'a': hi();
    case 'b': ho(); break;
    case 'c': he();
    case 'd': ha(); break;
}
.  .  .

can be written as:
if (a == 'a') {	
    hi(); goto do2; /* skip the test on 2 */
}
if (a == 'b') {
do2:
    ho(); goto done;	/* do a break */
}
if (a == 'c') {
    he(); goto do4; /* skip the test on 4 */
}
if (a == 'd') {
do4:
    ha(); goto done; /* do a break */
}
done:
.  .  .

A bit different than the simple if else block, ja?
The switch statement can also be coded as a jump table with generaly better
performance than the if else block.

It might be feasable to fold if else blocks testing the same variable repeatedly
into a jump table, but I'll wager it's unusual.
--j.a.tainter