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I didn't see where in the library at-xy was, so I cobbled one together using kernal plot:
: at-xy xr c! yr c! 0 sr c! $fff0 sys ;
Do you think it might be worth including somewhere?
It doesn't preserve interrupt disable, which might be something to improve. In assembly it would use CLC.
The routine itself would be grouped with page and emit, so I guess the norm here is assembly routines in io.asm.
I did the exercise to convert to code:
code at-xy ( x y -- )
clc,
w stx,
\ w 1+ sty,
lsb 1+ ldy,x
lsb lda,x \ had no ldx,x
tax,
$fff0 jsr,
w ldx,
\ w 1+ ldy,
inx,
inx,
;code
That also worked. It's rather cumbersome code, though, mostly dealing with ABI conversion. Still size reports the code version as smaller than the sys version.
Evidently, I am a total newbie at 6502 assembly.