SUBR:  MOV R1, -(R6)
        MOV R2, -(R6)
        MOV R3, -(R6)

        CLR R0   ; sum
        MOV R6, R1
        MOV #4, R2
        ADD R2, R1  ; skip over three saved registers, ret addr
        MOV @R1, R2  ; second parameter, now how many are left
        INC R1
        MOV @R1, R1  ; first parameter, now pointer to current array element

        ; post-tested loop ok because guaranteed n>0
 LOOP:  MOV (R1)+, R3
        ADD R3, R0
        BVS RETURN  ; with overflow flag set
        DEC R2
        TST R2
        BGT LOOP
        ; at this point R2=0, thus V is not set

RETURN: MOV (R6)+, R3
        MOV (R6)+, R2
        MOV (R6)+, R1
        RTS