; euclid.a65
; A program to find the greatest common divisor of two numbers

.ORG $1000

; .algo
LDA $00    ; Load from F to A
; .algo_
sec        ; Set carry flag
SBC $01    ; Subtract S from the number in A (from F)
BEQ end    ; Jump to .end if the difference is zero
BMI swap   ; Jump to .swap if the difference is negative
STA $00    ; Load A to F
JMP algo_  ; Jump to .algo_

; .end
end:
LDA $00    ; Load from F to A
BRK        ; Break (end program)

; .swap
swap:
LDX $00    ; Load F to X
LDY $01    ; Load S to Y
STX $01    ; Store X to S
STY $00    ; Store Y to F
JMP algo   ; Jump to .algo

algo:
JMP algo   ; Infinite loop to prevent program from ending

algo_:
JMP algo_  ; Infinite loop to prevent program from ending