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From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: net.lang.c
Subject: Re: case stmt != jumptable of goto labels  !!!!!!!!!
Message-ID: <553@hoptoad.uucp>
Date: Mon, 24-Feb-86 22:37:44 EST
Article-I.D.: hoptoad.553
Posted: Mon Feb 24 22:37:44 1986
Date-Received: Fri, 28-Feb-86 06:53:10 EST
References: <324@yetti.UUCP>
Organization: Nebula Consultants in San Francisco
Lines: 23
Keywords: case, jumptable

It is true that a case (in C, "switch") statement is not the same
as a jump vector, because the vector cannot be modified.  However,
a trivial hack gives the behaviour you want:

	int vector[MAX_JUMPS];

	switch (vector[i]) {

This costs one subscripting operation per jump -- a price, but a small price.
Not nearly the overhead of a function call, for example.  I've seen exactly
this kind of contruct used for the inner loop of an interpreter.  It
probably works OK for a regular expression scanner, or lexer, too.

You can even do it one better by declaring

	int *vector;

and pointing it at whatever jump table you are currently interested in,
out of a set of precompiled or dynamically built jump tables.

Are we having done yet?
-- 
John Gilmore  {sun,ptsfa,lll-crg,ihnp4}!hoptoad!gnu   jgilmore@lll-crg.arpa