Reversi moves

        !to "test.prg", cbm
        !convtab pet

        chrout = $ffd2
        getchr = $ffe4

        turn_length = $02
        xt = $9e
        yt = $9f
        xd = $b0
        yd = $b1
        current_player = $b2
        buffer_length = $b3
        x = $b4
        y = $b5

        * = $c000

        ldy #63                 ; Init board, current_player & other_player_mod
        lda #"."
-       sta board,y
        dey
        bpl -
        lda #"w"
        sta current_player
        sta board + 3*8+3
        sta board + 4*8+4
        lda #"b"
        sta other_player_mod+1
        sta board + 3*8+4
        sta board + 4*8+3

        jmp print_board

main_loop
        lda #0                  ; Read line into buffer.
        sta buffer_length
-       jsr getchr
        beq -
        ldy buffer_length
        sta buffer,y
        inc buffer_length
        cmp #3                  ; RUN/STOP
        beq exit
        jsr chrout
        cmp #13                 ; RETURN
        bne -

        ldy #end_txt_length - 1 ; buffer == "end\n" ?
-       lda buffer,y
        cmp end_txt,y
        bne +
        dey
        bpl -
exit
        rts
+
        lda buffer              ; convert coordinate
        sec
        sbc #"a"
        sta x
        lda buffer+1
        clc
        sbc #"0"
        sta y

        asl                     ; board(x,y) = current_player
        asl
        asl
        ora x
        tay
        lda current_player
        sta board,y

        lda #-1                 ; for xd = -1 to...
        sta xd
outer_loop
        lda #-1                 ; for yd = -1 to...
        sta yd
inner_loop
        ;lda yd                  ; if (xd | yd) = 0 then continue.
        ora xd
        beq inner_loop_continue
        lda x                   ; xt, yt = x, y
        sta xt
        lda y
        sta yt
        lda #0                  ; turn_length = 0
        sta turn_length

check_line_loop
        clc                     ; xt += xd
        lda xt
        adc xd
        sta xt
        clc                     ; yt += yd
        lda yt
        adc yd
        sta yt

        ;lda yt                  ; check if xt and yt between 0 and 7
        ora xt
        and #%11111000
        bne no_turns

        lda yt                  ; Y = yt*8+xt
        asl
        asl
        asl
        ora xt
        tay

        lda board,y             ; A = board(xt,yt)
other_player_mod                ; A != other_player ?
        cmp #0
        bne line_end

        tya                     ; store index into board in turn_coordinates.
        ldy turn_length
        sta turn_coordinates,y
        inc turn_length
        bne check_line_loop

line_end
        cmp current_player      ; board(xt,yt) == current_player ?
        beq check_line_loop_end
no_turns
        lda #0
        sta turn_length
check_line_loop_end

        lda turn_length         ; turns ?
        beq skip_turn_loop
        tay                     ; do turns.
        lda current_player
turn_loop
        ldx turn_coordinates-1,y
        sta board,x
        dey
        bne turn_loop
skip_turn_loop

inner_loop_continue
        inc yd                  ; next yd
        lda yd
        cmp #2
        bne inner_loop

        inc xd                  ; next xd
        lda xd
        cmp #2
        bne outer_loop

        lda current_player      ; swap players.
        ldy other_player_mod+1
        sta other_player_mod+1
        sty current_player

print_board
        ldy #0
print_loop
        tya                     ; index divisible by 8 ?
        and #%00000111
        bne +
        lda #13                 ; print newline.
        jsr chrout
+       lda board,y
        jsr chrout
        iny
        cpy #64
        bne print_loop
        lda #13
        jsr chrout

        jmp main_loop
;--------------------------------------
!align 255, 0, 0
end_txt
        !pet "end", 13
        end_txt_length = * - end_txt
;--------------------------------------
!align 255, 0, 0
board
        !fill 64
buffer
        !fill 16
turn_coordinates
        !fill 8