Re: What is byte-code ?

Anton Ertl wrote:


(snip regarding switch statements or statement label arrays)


>>This will save you about 2 jumps per instructoin since the jump tables
>>that are usually spit out by compilers are:


>>jump ip+(constant*case)
>>jump CODE_THAT_ACTUALLY_DOES_CASE_0
>>jump CODE_THAT_ACTUALLY_DOES_CASE_1


> I have never seen that kind of code generated. Which compiler does it
> that way? Big, dense switch statements have been translated into a
> range check, an array access (for the target address), and an indirect
> jump to the target in the code I looked at (usually by gcc).


IBM S/360 (S/370, ESA/390, etc.) compilers generate that for computed
GOTO in Fortran, and switch in languages with that.


S/360 has pretty much only one memory addressing mode with is
12 bit constant plus register plus register.


The exit codes (return codes) of all IBM supplied S/360 programs are
multiples of four, convenient for use in indexed branch instructions.
(Hopefully after bounds testing.)


-- glen

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