Is A Number Prime?

Write a function is$\_$prime that takes a single $($unsigned integer$)$ argument $($which you can assume is $>1),$ and returns $1$ if it's a prime number, and $0$ otherwise. We aren't going to worry about a clever algorithm here: we will simply check every number from $2$ to n$-1$ to see if it divides n:

def is$\_$prime$($n$)$:

i $=2$

while i $<$ n:

if n $\%$ i $==0$:

return $0$

i $+=1$

return $1$

The div instruction divides unsigned integers and calculates their remainder, but it's unusual. It always divides the value $\%$rdx:$\%$rax $($i$.$e$.$ a $128$ bit value with the high bits stored in $\%$rdx and the lower bits in $\%$rax$)$ by its single operand. It always leaves the quotient in $\%$rax and remainder in $\%$rdx$.$

You can get $\%$rdi divided by $\%$r$8$ in $\%$rax and remainder in $\%$rdx like this. The first two instructions set $\%$rdx:$\%$rax to the value from $\%$rdi $($by putting bunch of leading zeros in $\%$rdx$).$

mov $$0,\%$rdx

mov $\%$rdi, $\%$rax

div $\%$r$8$