;
; main routine: establish the stack, then read
; and write.
;
;  recursive multiplication.  assumes
;  b is positive.
; 
;  int mult(int a, int b){
;    if( b <= 0 ){
;      return 0
;    else
;      return a + mult(a, b-1)
;   }
;
        lcw r1 stack        ; set up stack
        
        loa r3 r0           ; get first parameter
        loa r2 r0           ; get second parameter
        psh r2              ; put second parameter on the stack

        lcw r2 mult         ; call mult
        cal r2 r2           ;

        pop r0              ; just for consistency, clean up the stack

        sto r3 r0           ; write result,
        hlt                 ;    and halt

mult
        psh r2             ; save the return address
        loa r2 r1 4         ; get at the 2nd argument, b
                            ; a = r2, b = r3

        bgt r2 r0 else      ; 0 < r2, i.e. recursive case
        add r3 r0 0         ; return 0
        brs endif
else
        sub r2 r2 1         ; r2 = a-1

        psh r3              ; save first argument, a, on stack (it's going to get overwritten by the return!)
        psh r2              ; add r2 as 2nd argument, r3 shouldn't have changed
        lcw r2 mult         ; call mult recursively
        cal r2 r2
        pop r0              ; remove 2nd argument (b-1) off stack

        pop r2              ; load 'a' back into r2 off of the stack
        add r3 r3 r2        ; r3 = a + mult(a, b-1)
endif
        pop r2              ; get the return address
        jmp r2              ; return

;
; stack area: 50 words
;
        dat 100
stack