;;; Read in three numbers and write out their gcd

allocate-registers zero, old-x, x, y, end, gcd
; set up constants
li zero, 0
read x
read y
li end, Lmiddle
li gcd, Lgcd

; calculate the gcd of x, y into x and then jump to end
Lgcd:
jeqz y, end
add old-x, x, zero
add x, y, zero
rem y, old-x, y
j gcd

Lmiddle:
; put third number into y and do a second gcd computation
read y
li end, Lend
j gcd

Lend:
write x
halt