On Wed, 8 Sep 2010, pito wrote:
> A version with unused registers, crashes (anforth 4.0,
> assembler.frt).
>
> \ Manual v 4.0 : The registers from R10 to R13 are currently unused,
>
> \ but may be used for the VM extended registers X and Y sometimes.
>
> code ++_ \ ( x1 x2 x3 -- x4 )
Looking at my assembly listing:
.def temp0 = r16
.def temp1 = r17
.def tosl = r24
.def tosh = r25
PFA_PLUS:
C:0039ab 9109 ld temp0, Y+
C:0039ac 9119 ld temp1, Y+
C:0039ad 0f80 add tosl, temp0
C:0039ae 1f91 adc tosh, temp1
C:0039af ce5e rjmp DO_NEXT
So, that means that simple
ld temp0, Y+
ld temp1, Y+
add tosl, temp0
adc tosh, temp1
ld temp0, Y+
ld temp1, Y+
add tosl, temp0
adc tosh, temp1
rjmp DO_NEXT
should do the trick. Doing in Forth:
R16 constant temp0
R17 constant temp1
R24 constant tosl
R25 constant tosh
code ++_
temp0 Y+ ld,
temp1 Y+ ld,
tosl temp0 add,
tosh temp1 adc,
temp0 Y+ ld,
temp1 Y+ ld,
tosl temp0 add,
tosh temp1 adc,
end-code
hex
1000 100 10 ++_ .
1110 ok
1111 222 33 ++_ .
1366 ok
It's really beneficial to study existing assembler
code! It also is immediately clear that ++_ is
the equivalent of + + - what I did is just + operation
inlined twice.
--Marcin
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