World: r3wp

but in fact it can be occured in one opcode of  length 1, if the 
adress is already contained in one 16 bit register .

that's mostly the case

so, the correct answer is: 1

What happens if you EXT8 a value that already has data in the higher 
bytes? I'm guessing it will just overwrite that data...

wrong

What happens? I don't have rebcode here to test.

I'm going off docs and memory here.

ext8 (128 + 65536) = -128 instead of 128

fooooollll

no it works

ext 128 = -128

I'm thinking that you may be able to efficiently store your 8-bit 
registers in your 16-bit registers and break them out when you need 
them.

Internally, they would really be 32-bit registers, of course.

Is the accumulator internally 8 or 16-bit?

8

it is A

_a in my source

What do 16-bit arithmetic instructions use for an accumulator?

HL

but most of instructions act on A

Is 8-bit or 16-bit code more common?

8 bit

because it's more compact and faster

and many operations occur only on 8 bit registers

like rotation operations

and bit manipulations

but the first reason is that 8bit register operations are faster

Well, there is no reason to change that balance - the code expects 
it. 16-bit operations can be sped up using a few tricks if necessary, 
like temporary registers that are used internally. You can even name 
those registers _bc, _de and _hl if you like :)

Do the rotation instructions affect the carry flag?

some of them, it's an option

the carry flag can be injected to the left or to the right

or not

there are 12 different rotations

Z80 is good with rotation

How does your code handle exchanges?

badly

label EXX
	set.i tmp _b set.i _b _b' set.i _b' tmp 
	set.i tmp _c set.i _c _c' set.i _c' tmp
	set.i tmp _d set.i _d _d' set.i _d' tmp
	set.i tmp _e set.i _e _e' set.i _e' tmp
	set.i tmp _h set.i _h _h' set.i _h' tmp
	set.i tmp _l set.i _l _l' set.i _l' tmp
	(cont)

exchange of  b, c, d ,e , h , l, with b' , c', d', e', h', l'

It could be worse.

i don't see how :-)

You could be accessing all of those values indirectly to make the 
swap easier, but slowing down everything else :)

yeah or i could build another instance of the interpreter and swap 
them

Mwahahaha

I thought of that, except in my head it was a second set of BRAB 
blocks :)

so, to conclude this session, Rebcode needs union handling and swap 
instruction.

I was thinking vectors and opcodes to handle the struct! type, but 
a swap instruction would be nice too.

I would love a REBOL native swap instruction that worked like block 
set, but we all have dreams :)

good night Brian

Limited use though.

Good night.