*-----------------------------------------------------------
* Program    :  Postifx
* Written by :  Conner Wingard
* Date       :  11/18/2010
* Description:  rpn calculator
*-----------------------------------------------------------
    ORG $1000


START:              ; first instruction of program


    LEA welcome,A1
    MOVE.B  #14,D0
    TRAP    #15
    MOVE.B  #0,D6
    MOVE.B  #0,D5


LOOP    LEA message,A1
    MOVE.B  #14,D0
    TRAP    #15

    MOVE.B  #5,D0
    TRAP    #15
    CMP.B   #43,D1
    BEQ PUSHOP
    CMP.B   #45,D1
    BEQ PUSHOP
    CMP.B   #42,D1
    BEQ PUSHOP
    CMP #64,D1  ;ascii code for @
    BEQ EVAL_2

    MOVE.B  D1,-(SP)
    BRA LOOP

PUSHOP  MOVE.B  D1,-(A2)    ; push op to op stack
    ADD.B   #1,D6   ; add to current number of operators
    BRA LOOP
ADDFUNC CLR.B   D3
    CLR.B   D4

    MOVE.B  (SP)+,D3  ; pop MSW word at SP to D2
    MOVE.B  (SP)+,D4

    SUB     #'0',D3
    SUB #'0',D4

    ADD.B   D3,D4
    MOVE.B  D4,-(SP)
    SUB.B   #1,D6

    BRA EVAL_2

MINFUNC CLR.B   D3
    CLR.B   D4

    MOVE.B  (SP)+,D3  ; pop MSW word at SP to D2
    MOVE.B  (SP)+,D4
    SUB     #'0',D3
    SUB #'0',D4

    SUB.B   D3,D4
    MOVE.B  D4,-(SP)
    SUB.B   #1,D6

    BRA EVAL_2

MULFUNC CLR.B   D3
    CLR.B   D4

    MOVE.B  (SP)+,D3  ; pop MSW word at SP to D2
    MOVE.B  (SP)+,D4
    SUB     #'0',D3
    SUB #'0',D4

    MULU    D3,D4
    MOVE.B  D4,-(SP)
    SUB.B   #1,D6

    BRA EVAL_2

EVAL_2  CLR.B   D1
    CLR.B   D7
    CMP.B   #0,D6
    BEQ DONE


    MOVE.B  (A2)+,D7
    CMP.B   #43,D7
    BEQ ADDFUNC
    CMP.B   #45,D7
    BEQ MINFUNC
    CMP.B   #42,D7
    BEQ MULFUNC

    BRA EVAL_2

*-------------TERMINATE---------------------------
DONE    CLR.B   D1
    MOVE.B  (SP)+,D1
    *SUB    #'0',D1
    MOVE.B  #3,D0
    TRAP    #15

    LEA bye,A1
    MOVE.B  #14,D0 ; say bye
    TRAP    #15

    MOVE.B  #9,D0
    TRAP    #15     ; halt simulator

* Variables and Strings

CR  EQU $0D     ; Carriage return
LF  EQU $0A     ; line feed
Bye DC.B    CR,LF,'Bye now!',0
Message DC.B    CR,LF,'Enter Expression: ',0


    END START       ; last line of source