DisplayResult2

    AREA    DisplayResult, CODE, READONLY
    IMPORT  main
    IMPORT  getkey
    IMPORT  sendchar
    EXPORT  start
    PRESERVE8

start
    LDR R4, =0x0    ; clear register        First number enetered by user
    LDR R6, =0x0    ; clear register        Second number entered by user
    LDR R10, =10    ;
    LDR R12, =0     ; clear register        Set to 0xFFFFFFFF if invalid input

readFirstNum
    BL  getkey      ; read key from console
    CMP R0, #0x0D   ; while (key != CR)
    BEQ endRead     ; {
    BL  sendchar    ;   echo key back to console

    CMP R0, #'+'    ; while (key != +)
    BEQ isAdd       ;
    CMP R0, #'-'    ; && while (key != -)
    BEQ isSub       ;
    CMP R0, #'*'    ; && while (key != *)
    BEQ isMul       ;
    CMP R0, #'/'    ; && while (key != /)
    BEQ isDiv       ;
    CMP R0, #'%'    ; && while (key != %)
    BEQ isMod       ;
    CMP R0, #'!'    ; && while (key != !)
    BEQ isFac       ; {

    SUB R0, R0, #0x30 ; convert from ASCII to actual number
    MUL R4, R10, R4 ; move numbers one step to the left (from decimal point)
    ADD R4, R4, R0  ; add next number entered by the user to the previous

    B   readFirstNum ; }

isAdd               ;
    LDR R7, ='+'    ; store + operator in R7
    B readSecondNum ;

isSub               ;
    LDR R7, ='-'    ; store - operator in R7
    B readSecondNum ;

isMul               ;
    LDR R7, ='*'    ; store * operator in R7
    B readSecondNum ;

isDiv
    LDR R7, ='/'    ; store / operator in R7
    B readSecondNum ;

isMod
    LDR R7, ='%'    ; store % operator in R7
    B readSecondNum ;

isFac
    LDR R7, ='!'    ; store ! operator in R7
    CMP R0, #0x0D   ; while (key != CR)
    BEQ endRead     ;

readSecondNum
    BL  getkey      ; read key from console
    CMP R0, #0x0D   ; while (key != CR)
    BEQ endRead     ; {
    BL  sendchar    ;   echo key back to console

    SUB R0, R0, #0x30 ; convert from ASCII to actual number
    MUL R6, R10, R6 ; move numbers one step to the left (from decimal point)
    ADD R6, R6, R0  ; add next number entered by the user to the previous

    B   readSecondNum       ; }

endRead

    CMP R7, #'+'
    BEQ addCalc
    CMP R7, #'-'
    BEQ subCalc
    CMP R7, #'*'
    BEQ mulCalc
    CMP R7, #'/'
    BEQ divCalc
    CMP R7, #'%'
    BEQ modCalc
    CMP R7, #'!'
    BEQ facCalc
    B invalidInput      ;

addCalc
    ADD R5, R4, R6
    B endCalc

subCalc
    CMP R4, R6
    BLO invalidInput
    SUB R5, R4, R6
    B endCalc

mulCalc
    MUL R5, R4, R6
    B endCalc


divCalc
    LDR R0, =0      ; quotient          First number entered by user = a
    MOV R1, R4      ; remainder = a     Second number entered by user = b
zeroCheck
    CMP R6, #0
    BEQ invalidInput
whRemGTb
    CMP R1, R6      ; while (remainder >=b)
    BLO endDivCalc  ;
    ADD R0, R0, #1  ; quotient = quotient + 1
    SUB R1, R1, R6  ; remainder = remainder - b
    B   whRemGTb    ;
endDivCalc
    MOV R5, R0
    MOV R8, R1
    B endCalc


modCalc
    LDR R0, =0      ; quotient          First number entered by user = a
    MOV R1, R4      ; remainder = a     Second number entered by user = b
zero
    CMP R6, #0
    BEQ invalidInput
whRemGTQuo
    CMP R1, R6      ; while (remainder >=b)
    BLO endModCalc  ;
    ADD R0, R0, #1  ; quotient = quotient + 1
    SUB R1, R1, R6  ; remainder = remainder - b
    B   whRemGTQuo  ;
endModCalc
    MOV R5, R1
    B endCalc


facCalc
    LDR R1, =1      ; result = 1
    CMP R4, #13
    BHS invalidInput
facMul
    CMP R4, #1      ; while (number > 1)
    BLS endFacCalc  ; {
    MUL R1, R4, R1  ; result = number * result
    SUB R4, R4, #1  ; number = number - 1
    B facMul        ; }
endFacCalc
    MOV R5, R1      ; move result to R5
    B endCalc

invalidInput        ;                       ****************************************
    LDR R12, =0XFFFFFFFF    ;   Used to indicate invalid input
    B invalidInOutput

endCalc

    LDR R0, ='='    ; print =
    BL sendchar

    LDR R11, =1000000000
    CMP R5, R11
    BHS billion
    LDR R11, =100000000
    CMP R5, R11
    BHS hundredMillion
    LDR R11, =10000000
    CMP R5, R11
    BHS tenMillion
    LDR R11, =1000000
    CMP R5, R11
    BHS million
    LDR R11, =100000
    CMP R5, R11
    BHS hundredThousand
    LDR R11, =10000
    CMP R5, R11
    BHS tenThousand
    LDR R11, =1000
    CMP R5, R11
    BHS thousand
    CMP R5, #100
    BHS hundred
    CMP R5, #10
    BHS ten
    B singleDigit           ; *********************************

billion
    LDR R9, =0      ; quotient
    MOV R10, R5     ; remainder = a
whBillion
    CMP R10, R11            ; while (remainder >=billion)
    BLS endBillion          ;
    ADD R9, R9, #1          ; quotient = quotient + 1
    SUB R10, R10, R11       ; remainder = remainder - b
    B   whBillion       ;
endBillion
    MOV R0, R9
    ADD R0, R0, #'0'
    BL sendchar
    MOV R5, R10
    ;B stop


;divByTen
;   LDR R0, =0      ; quotient
;   MOV R1, R11     ; remainder = a
;zeroCheck3
;   CMP R1, #0
;   BEQ endDivTen
;whGTzero
;   CMP R1, #10     ; while (remainder >=b)
;   BLO stop    ;
;   ADD R0, R0, #1  ; quotient = quotient + 1
;   SUB R1, R1, #10 ; remainder = remainder - b
;   B   whGTzero    ;
;endDivTen
;   MOV R11, R0
;   B billion



hundredMillion
    LDR R9, =0      ; quotient
    LDR R11, =100000000
    MOV R10, R5     ; remainder = a
whHundredMillion
    CMP R10, R11            ; while (remainder >=hundredMillion)
    BLS endHundredMillion   ;
    ADD R9, R9, #1          ; quotient = quotient + 1
    SUB R10, R10, R11       ; remainder = remainder - b
    B   whHundredMillion        ;
endHundredMillion
    MOV R0, R9
    ADD R0, R0, #'0'
    BL sendchar
    MOV R5, R10

tenMillion
    LDR R9, =0      ; quotient
    LDR R11, =10000000
    MOV R10, R5     ; remainder = a
whTenMillion
    CMP R10, R11            ; while (remainder >=tenMillion)
    BLS endTenMillion   ;
    ADD R9, R9, #1          ; quotient = quotient + 1
    SUB R10, R10, R11       ; remainder = remainder - b
    B   whTenMillion        ;
endTenMillion
    MOV R0, R9
    ADD R0, R0, #'0'
    BL sendchar
    MOV R5, R10


million
    LDR R9, =0      ; quotient
    LDR R11, =1000000
    MOV R10, R5     ; remainder = a
whMillion
    CMP R10, R11            ; while (remainder >=million)
    BLS endMillion  ;
    ADD R9, R9, #1          ; quotient = quotient + 1
    SUB R10, R10, R11       ; remainder = remainder - b
    B   whMillion       ;
endMillion
    MOV R0, R9
    ADD R0, R0, #'0'
    BL sendchar
    MOV R5, R10

hundredThousand
    LDR R9, =0      ; quotient
    LDR R11, =100000
    MOV R10, R5     ; remainder = a
whHundredThousand
    CMP R10, R11            ; while (remainder >=hundredThousand)
    BLS endHundredThousand  ;
    ADD R9, R9, #1          ; quotient = quotient + 1
    SUB R10, R10, R11       ; remainder = remainder - b
    B   whHundredThousand   ;
endHundredThousand
    MOV R0, R9
    ADD R0, R0, #'0'
    BL sendchar
    MOV R5, R10

tenThousand
    LDR R9, =0      ; quotient
    LDR R11, =10000
    MOV R10, R5     ; remainder = a
whTenThousand
    CMP R10, R11            ; while (remainder >=tenThousand)
    BLS endTenThousand  ;
    ADD R9, R9, #1          ; quotient = quotient + 1
    SUB R10, R10, R11       ; remainder = remainder - b
    B   whTenThousand   ;
endTenThousand
    MOV R0, R9
    ADD R0, R0, #'0'
    BL sendchar
    MOV R5, R10

thousand
    LDR R9, =0      ; quotient
    LDR R11, =1000
    MOV R10, R5     ; remainder = a
whThousand
    CMP R10, R11            ; while (remainder >=thousand)
    BLS endThousand ;
    ADD R9, R9, #1          ; quotient = quotient + 1
    SUB R10, R10, R11       ; remainder = remainder - b
    B   whThousand  ;
endThousand
    MOV R0, R9
    ADD R0, R0, #'0'
    BL sendchar
    MOV R5, R10

hundred
    LDR R9, =0              ; quotient
    LDR R11, =100
    MOV R10, R5             ; remainder = a
whHundred
    CMP R10, R11            ; while (remainder >=hundred)
    BLS endHundred          ;
    ADD R9, R9, #1          ; quotient = quotient + 1
    SUB R10, R10, R11       ; remainder = remainder - b
    B   whHundred           ;
endHundred
    MOV R0, R9
    ADD R0, R0, #'0'
    BL sendchar
    MOV R5, R10

ten
    LDR R9, =0              ; quotient
    LDR R11, =10
    MOV R10, R5             ; remainder = a
whTen
    CMP R10, R11            ; while (remainder >=ten)
    BLS endTen              ;
    ADD R9, R9, #1          ; quotient = quotient + 1
    SUB R10, R10, R11       ; remainder = remainder - b
    B   whTen   ;
endTen
    MOV R0, R9
    ADD R0, R0, #'0'
    BL sendchar
    MOV R5, R10

singleDigit
    MOV R0, R5
    ADD R0, R0, #'0'
    BL sendchar

divRemainder
    CMP R7, #'/'
    BNE stop
    LDR R0, ='r'
    BL sendchar
    MOV R0, R8
    ADD R0, R0, #'0'
    BL sendchar
    B stop



invalidInOutput
    LDR R9, =invalidInStr   ;   invalidInStr    ; address = invalid input string
    LDRB R0, [R9]           ;
whInvStr
    CMP R0, #0              ;
    BEQ endWhInv
    BL sendchar
    ADD R9, R9, #1
    LDRB R0, [R9]
    B whInvStr
endWhInv


stop    B   stop


    AREA invalidInOutputData, DATA, READWRITE

invalidInStr
    DCB     " = Invalid Input! Please try again. ",0    ;   Null terminated invalid input string

    END