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|
;;;
;; A silly example that tries to demonstrate how to use list.nes.
;;
;; It will initialize a list of 256 16-bit items with a value of 0..255
;; respectively. After doing that, it will multiply each value by 2 and store it
;; again. As a final touch, the second item will be forced to have the same
;; value for the high and the low bytes.
;;
;; You can check that this works by running `make example` and then running the
;; resulting ROM file into an emulator with a RAM inspector like FCEUX or Mesen.
;; Then go from memory address $0400 onwards and check that the results are as
;; described.
.include "../test/common.s"
main:
LIST_INIT $0400
;; We will store 256 16-bit items and $90 will keep track of it.
lda #0
sta $90
@fill_loop:
;; The 16-bit item will have the value of the current index as stored in
;; $90. The list will be initialized through the `List::push` function, so
;; the size is properly set at the end.
lda $90
jsr List::push
lda #0
jsr List::push
;; If we have set all the items we wanted, move into the next thing,
;; otherwise increase $90 and go back into the loop.
lda $90
cmp #$FF
beq @set
inc $90
jmp @fill_loop
@set:
;; Reset the pointer to the start of the list since we want to iterate it
;; over.
LIST_IT_FROM $0400
@set_loop:
;; There are two values to keep track: `List::ptr` and `List::ptr + 1`. For
;; the low byte we need to shift left once, and then the high byte needs to
;; add the possible carry to itself. In order to do this and call
;; `List::set` properly we need to be do some stuff with the stack (low
;; byte) or the `x` register (high byte).
ldy #0
lda (List::ptr), y
asl
pha
lda #0
iny
adc (List::ptr), y
tax
;; Pull the value that corresponds to the low byte and set it. After doing
;; that, though, did we get a $FF value? If so then it means that we are
;; done with it, otherwise proceed to grab the high byte stored on the `x`
;; registerm set it with `List::set` and loop again.
pla
jsr List::set
cpy #$FF
beq @final_get
txa
jsr List::set
jmp @set_loop
@final_get:
;; We are done! Now for a final touch let's copy the value from the low byte
;; into the high byte of the second element.
LIST_IT_FROM $0402
jsr List::get
jsr List::set
done:
jmp done
|
