Re: Switch statement code generation

Joshua Cranmer <Pidgeot18@verizon.invalid>
Wed, 04 Nov 2009 07:38:43 -0500

          From comp.compilers
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[6 later articles]
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From: Joshua Cranmer <Pidgeot18@verizon.invalid>
Newsgroups: comp.compilers
Date: Wed, 04 Nov 2009 07:38:43 -0500
Organization: Georgia Institute of Technology
References: 09-11-002 09-11-003
Keywords: code
Posted-Date: 05 Nov 2009 15:17:44 EST

On 11/04/2009 12:27 AM, glen herrmannsfeldt wrote:
> I believe that JVM also has a special instruction for this
> operation, as the above likely don't work there.


Actually two special bytecodes, lookupswitch and tableswitch. These are
the linear scan and the jump table methods, respectively. The upcoming
string switch appears to use a hash routine.


> [On machines with condition codes, I've seen binary searches expanded
> into code with compare and branch instructions; after the comparison
> you can do a three way branch on less, equal, or greater. -John]


It seems both gcc and llvm emit code like this; I've added it to my list
already.


--
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth


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