.BLKW   1000.               ;
START:      MOV     #START, SP          ;INIT SP
            SUB     #8., SP             ;INC STACK
            MOV     N,  4(SP)           ;MOV N INTO THE FIRST STACK
            MOV     M,  6(SP)           ;MOV M INTO THE FIRST STACK
            MOV     #RET, 0(SP)         ;
            JMP     EXPO                ;
RET:        MOV     2(SP), RES          ;
            ADD     #8., SP             ;
            HALT                        ;
N:          .BLKW   1                   ;
RES:        .BLKW   1                   ;

EXPO:       TST     4(SP)               ;
            BEQ     BASIS               ;
            MOV     4(SP), R0           ;
            DEC     R0                  ;
            SUB     #8., SP             ;
            MOV     R0, 4(SP)           ;
            MOV     M,  6(SP)           ;
            ASL     R0                  ;
            BCS     EVEN                ;
            ASR     R0                  ;
            MOV     #RRET, 0(SP)        ;
            BR      SKIP                ;
EVEN:       MOV     R0, 4(SP)           ;
            MOV     #DIVE               ;
SKIP:       JMP     EXPO                ;
RRET:       MOV     2(SP), R1           ;
            ADD     #8., SP             ;
            MUL     6(SP), R1           ;
            MOV     R1, 2(SP)           ;
            JMP     @0(SP)              ;
DIVE:       MOV     2(SP), R1           ;
            ADD     #8., SP             ;
            MUL     6(SP), #2           ;
            ASL     4(SP)               ;
            MOV     R1, 2(SP)           ;
            JMP     @0(SP)              ;
BASIS:      MOV     #1, 2(SP)           ;
            JMP     @0(SP)              ;
            .END                        ;