; What is the largest prime factor of the number 600851475143 ?
extern printf
SECTION .data
flag:   db  "%d",10,0           ; "%d\n\0"

SECTION .text
    global main    

main:
        push rbp                ; set up stack
        mov rbp, rsp


        mov rcx, 2              ; smallest prime factor: 2
        mov rax, 0x8BE589EAC7   ; target = 600851475143

.loop   xor rdx, rdx            ; clear rdx (remainder)
        push rax
        div rcx                 ; divide rdx:rax/rcx
        cmp rdx, 0              ; compare only remainder
        jnz .next               ; if r = 0 , its a factor
                                ; we already divided the number so
                                ; we just need to save the value in rax
                                ; as the new number to factorize
        add rsp, 8              ; delete the old
        push rax
        mov rcx, 1              ; reset the counter (normally would start at 2,
                                ; but we increment anyway
.next   pop rax                 ; refresh value 
        inc rcx                 ; factor ++
        cmp rax, rcx            ; while rax > rcx  number > factor
                                ; i.e. not a prime factor
        jg .loop
        
        mov rdi, flag           ; arg 1 (format)
        mov rsi, rcx            ; arg 2 (value)
        mov rax, 0		; no xmm registers
        call printf wrt ..plt

        mov rsp, rbp            ; reset to the top of the stack
        pop rbp

        mov rax, 0
        ret