PRIME OR NOT

            AREA Prime_or_Not,code,readonly
            ENTRY
is_prime    mov r1, #2
            mov r2, #1

loop        cmp r0, r1
            bge found
            mov r3, r0
            bl mod
            cmp r0, #0
            bne not_prime
            add r1, r1, #1
            b loop

found       mov r0, r2
            bx lr

not_prime   mov r2, #0
            b loop

mod         push {r4, lr}
            mov r4, r1
            mov r1, #0

div_loop    cmp r3, r4
            blt done
            sub r3, r3, r4
            add r1, r1, #1
            b div_loop

done        mov r0, r3
            pop {r4, lr}
            bx lr

            END