*= $0       ; $00 = Zeropage, $10 = Stack

    .START Main
Zahl1   .DB $00
    *= * + 2    ; byte Zahl1[2]
Zahl2   .DB $00
    *= * + 2    ; byte Zahl2[2]
Real1   .DB $00
            ; byte Real1
Real2   .DB $00
            ; byte Real2
InputMsg .BYTE "Eingabe: ", $0

    *= $200
io_area = $e000
io_cls  = io_area + 0   ; io_cls()
io_putc = io_area + 1   ; io_putc()
io_putr = io_area + 2   ; io_putr()
io_puth = io_area + 3   ; io_puth()
io_getc = io_area + 4   ; io_getc()

mul_a   = $2006
mul_b   = $2007
mul_el  = $2000
mul_eh  = $2001
mul_ex  = $2002

Main:
            ; main()
    LDY #$0
            ; Y = 0x1
.GetKey
            ; while(Y < 2)
    LDA io_getc
    BEQ .GetKey
            ;   if !io_getc()   goto GetKey
    TAX
    TYA
    PHA
    TXA
            ;   [Push] Y by X=A -> A=Y -> [Push] A -> A=X
    PHA
    PHA     ;   [Push] A,A
    JSR IsNumber
    PLA
    BEQ .GetKey
            ;   if !IsNumber(A) goto GetKey else
    PLA
    STA io_putc
            ;   [Pop] A, io_putc()
    TAX
    PLA
    TAY

    TXA
            ;   [Pop] Y by X=A -> [Pop] A -> Y = A -> A = X
    SEC
    SBC #$30
            ;   A = A - 0x30
    STA Zahl1, Y
            ;   Zahl1[Y] = A

    TYA
    CMP #$2
    BEQ .GetKeyEnd
    INY
    JMP .GetKey
            ;   if Y == 2   goto GetKeyEnd  else
            ;                       Y++
            ;                       goto GetKey

.GetKeyEnd
    LDY #$0
    LDA Zahl1, Y
    STA mul_a
    LDA #$64
    STA mul_b
    JSR Mul
    LDA mul_el
    STA Real1
            ; Real1 = Mul(Zahl1[0], 0x64)
    LDY #$1
    LDA Zahl1, Y
    STA mul_a
    LDA #$a
    STA mul_b
    JSR Mul
    LDA mul_el
    CLC
    ADC Real1
    STA Real1
            ; Real1 = Real1 + Mul(Zahl1[1], 0xA)
    LDY #$2
    LDA Zahl1, Y
    CLC
    ADC Real1
    STA Real1
            ; Real1 = Real1 + Zahl1[2]

            ; io_puth(Real1)

    LDY $0
            ; Y = 0x0

.GetKey2
            ; while(Y < 2)
    LDA io_getc
    BEQ .GetKey2
            ;   if !io_getc()   goto GetKey
    TAX
    TYA
    PHA
    TXA
            ;   [Push] Y by X=A -> A=Y -> [Push] A -> A=X
    PHA
    PHA     ;   [Push] A,A
    JSR IsNumber
    PLA
    BEQ .GetKey2
            ;   if !IsNumber(A) goto GetKey else
    PLA
    STA io_putc
            ;   [Pop] A, io_putc()
    TAX
    PLA
    TAY

    TXA
            ;   [Pop] Y by X=A -> [Pop] A -> Y = A -> A = X
    SEC
    SBC #$30
            ;   A = A - 0x30
    STA Zahl2, Y
            ;   Zahl2[Y] = A

    TYA
    CMP #$2
    BEQ .GetKeyEnd2
    INY
    JMP .GetKey2
            ;   if Y == 2   goto GetKeyEnd  else
            ;                       Y++
            ;                       goto GetKey

.GetKeyEnd2
    LDY #$0
    LDA Zahl2, Y
    STA mul_a
    LDA #$64
    STA mul_b
    JSR Mul
    LDA mul_el
    STA Real2
            ; Real2 = Mul(Zahl2[0], 0x64)
    LDY #$1
    LDA Zahl2, Y
    STA mul_a
    LDA #$a
    STA mul_b
    JSR Mul
    LDA mul_el
    CLC
    ADC Real2
    STA Real2
            ; Real2 = Real2 + Mul(Zahl2[1], 0xA)
    LDY #$2
    LDA Zahl2, Y
    CLC
    ADC Real2
    STA Real2
            ; Real2 = Real2 + Zahl2[2]

    LDA Real2
    STA io_puth
            ; io_puth(Real2)

    BRK
            ; BRK()

    ; End of Programm, HALT

DisplayS:
            ; Display() ---> Later
    RTS


IsNumber:
            ; IsNumber()
    PLA
    TAX
    PLA
    TAY
            ; X, Y = [Top], [Top]

    PLA
            ; A = [Top]
    CMP #$30
    BCC .IsNumber_False
    CMP #$3a
    BCS .IsNumber_False
            ; if A < 0x30 && A >= 0x3a goto IsNumber_False
    LDA #$1
    PHA
    JMP .IsNumber_Return
            ; return 0x1;
.IsNumber_False
    LDA #$0
    PHA
            ; return 0x0;
.IsNumber_Return
    TYA
    PHA
    TXA
    PHA
    RTS

Add_16:
            ; Add_16()
    CLC
    LDA $2000
    ADC $2002
    STA $2000
            ; *(0x2000) = *(0x2000) + *(0x2002)
    LDA $2001
    ADC $2003
    STA $2001
    RTS
            ; return *(0x2001) = *(0x2001) + *(0x2003)

Mul:
            ; Mul()

    LDY #$00
    STY $2000
    STY $2001
            ; *(0x2000), *(0x2001) = 0x0
    LDA $2007
    BEQ .Mul_Exit

    STY $2003

.Mul_Init_Multiplicant

    LDY $2006
    STY $2002

.Mul_Next_Digit
    LSR

    TAY
    BCC .Mul_Skip_Add
            ; if *(0x2007) << 1 < [Pop] A   goto SKIP_ADD

.Mul_Add
    JSR Add_16
            ; ADD_16()

.Mul_Skip_Add
.Mul_Shift
            ; SkipAdd() = Shift()
    ASL $2002
    ROL $2003

    TYA
    BNE .Mul_Next_Digit
.Mul_Exit
    RTS