World: r3wp

i' made a Z80 emulator using rebcode (not complete), you can see 
it in galaga.r on rebol.org

Ah, that was you. Someone mentioned that one lately.

ah BrianH, i remember that you made the same proposal for my z80 
emu (peephole optimzation)

hard to do

interesting to do on ROMs (static analysis before to launch the code) 
but not valuable in RAM because the code can be modified

Steeva, about flags: e.g. the zero flag Z (bit 1 of P). In stead 
of that I set it each time A, X or Y become zero, I could save any 
of those (A, X or Y) in a variable, and then test on that var and 
set the flag correctly, if and when the flag is actual used. Is that 
what you mean?

and limited because on 6502 for example, many branchements are calculated 
(not statics)

yes Geomol, it's that

Flags are calculated on the last accumulator value if i don't do 
mistakes

ok. One optimization, I consider, is to cross-compile 6502 opcodes 
to rebcode, instead of emulating the 6502. That won't work with self-modifying 
code and branches will be a problem. So it's hard, but I think, it 
might work.

in theory

i give you an example with the TAX opcode

; updating flags in real time

label TAX
seti X A
eq X 0
either [or P 2] [and P 253]
seti i X
and i 128
eq i 128
either [or P 128] [and P 127]
bra continue

;  delay the calcul of flags

label TAX
seti X A

or maskA (2 + 128)     ; remember that we have to recalculate zero 
and negative flags using A, but don't do it now
bra continue

Thanks!

you got the idea ? ;-)

Yup! :)

did you think that using PC as an offset (integer) instead of as 
a serie could be faster ?

I should do a test before saying that

I didn't consider much in deep actually. It can be improved, I'm 
sure. :)

anyone happes to still have a rebol/core binary with rebcode functionality 
archived somewhere?

it's not in the download section of rebol.com anymore ?

ah, got it: http://www.rebol.net/builds/042/rebview1350042.tar.gz

resp. http://www.rebol.net/builds/031/rebview1350031.exefor windows