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From: guy@rlgvax.UUCP (Guy Harris)
Newsgroups: net.lang.c
Subject: Re: the C switch
Message-ID: <549@rlgvax.UUCP>
Date: Sun, 3-Mar-85 02:24:33 EST
Article-I.D.: rlgvax.549
Posted: Sun Mar  3 02:24:33 1985
Date-Received: Mon, 4-Mar-85 08:23:44 EST
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Organization: CCI Office Systems Group, Reston, VA
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> > Do any C compilers perform switch optimization? I.e. tradeoff cascaded if
> > for table lookup.
> 
> All the C compilers I am familiar with have about three different ways
> of generating code for a switch statement, in an attempt to optimize
> the size of the code vs. its speed.

Specifically, for a dense switch the VAX PCC generates a "casel" (indexed
branch) instruction.  For a sparse switch with a small number of cases, it
generates a cascaded "if".  For stuff in between, it either generates a linear
or hashed table search.  I believe the Ritchie PDP-11 C compiler generates
similar code; many other PCC implementations do also.

	Guy Harris
	{seismo,ihnp4,allegra}!rlgvax!guy
-- 
	Guy Harris
	{seismo,ihnp4,allegra}!rlgvax!guy