A question about bytecodes

[Ulf Zibis]

Very interesting, what you are doing. Good Luck !
I'm also often missing unsigned integers.

Unfortunately I can't answer your question.

-Ulf




Am 06.01.2009 14:00, Stephen Dawkins schrieb:
> Hi
>
> I've been hacking around on the JVM, attempting to add support for
> unsigned integers. I've managed to add several opcodes (based on baload,
> bipush, iinc, i2l, saload and sipush) that do zero-extending, rather than
> sign-extending.
>
> However, I came across a limit in the JVM. In bytecodes.cpp, there is this
> line:
>
> assert(number_of_codes <= 256, "too many bytecodes");
>
> My question is, why is the JVM itself limited to 256 bytecodes? I
> understand the class file is limited due to a bytecode being 1 byte long,
> but I am confused as to why there is a hard limit like this.
>
> The only place I've seen so far which requires the bytecode to be 1 byte,
> is the C++ interpreter which casts the opcode to a jbyte. Are there any
> other places that require a bytecode to be 1 byte long?
>
> I was hoping to implement unsigned integers by just adding an 'unsigned'
> opcode, followed by the the opcode to modify (baload, etc) then remap the
> opcode to a 'virtual' unsigned_baload opcode when loading the class into
> the JVM.
>
> Thanks & Regards
> Stephen
>
>
>