ZeroBE64$ = Chr$(0) + Chr$(0) + Chr$(0) + Chr$(0) + Chr$(0) + Chr$(0) + Chr$(0) + Chr$(0)
OneBE64$  = Chr$(0) + Chr$(0) + Chr$(0) + Chr$(0) + Chr$(0) + Chr$(0) + Chr$(0) + Chr$(1)

Function DumpBE64(A$)
    out$ = "0x"
    For I = 1 To 8
        out$ = out$ + Right$(Hex$(Asc(Mid$(A$, I))), 2)
    Next
    Print out$
End Function

Print "DumpBE64 Tests:"
DumpBE64 ZeroBE64$
DumpBE64 OneBE64$

;**
;* Converts an integer To String representation
;*
;* Returns the String representation of num. The conversion is done byte-wise
;* with the high-nibble First.
;*
;* @param num   An integer
;*
;* @Return The String representation of the given integer
;*/
Function EncodeBE64$(num)
    result$ = ""
    For I = 1 To 8
       result$ = Chr$(num And 255) + result$
       num     = num Shr 8
    Next
    Return result$
End Function

Print "EncodeBE64 Tests:"
DumpBE64 EncodeBE64$(1)
DumpBE64 EncodeBE64$(256)

;**
;* Converts a String representation to an integer
;*
;* Returns the integer representation of num$. The conversion is done byte-wise
;* with the high-nibble First.
;*
;* @param num$  An integer
;*
;* @Return The integer equivalent of the given string
;*/
Function DecodeBE64(num$)
    result = 0
    For I = 1 To 8
       A = Asc(Mid$(num$, I))
       If A < 0 Then A = 0
       result = result Shl 8 + A
    Next
    Return result
End Function

Print "DecodeBE64 Tests:"
Print DecodeBE64(ZeroBE64$)
Print DecodeBE64(OneBE64$)
Print DecodeBE64(EncodeBE64$(65535))

;Stop here if you have 64-bit interpreter
;A$ = EncodeBE64$($7fffffffffffffff)
;B$ = EncodeBE64$($0123456789ABCDEF)
;Q  = DecodeBE64(A$) / DecodeBE64(B$)
;R  = DecodeBE64(A$) Mod DecodeBE64(B$)
;Print Q ;Rem Windows Calc says "0x70"
;Print R ;Rem Windows Calc says "0x91A2B3C4D5E76F"
;C$ = EncodeBE64$(Q)
;D$ = EncodeBE64$(R)
;WaitKey
;End

;**
;* Compare two numbers
;*
;* Compares the num1 To the num2 And returns the result as an integer
;*
;* @param num1$ The Left operand, as a big-endian String
;* @param num2$ The Right operand, as a big-endian String
;*
;* @return Returns 0 If the two operands are equal, 1 If the num1 is larger
;*         than the num2, -1 otherwise
;*/
Function CompBE64(num1$, num2$)
    For I = 1 To 8
        A = Asc(Mid$(num1$, I))
        If A < 0 Then A = 0
        B = Asc(Mid$(num2$, I))
        If B < 0 Then B = 0
        If A < B Then Return -1
        If A > B Then Return 1
    Next
    Return 0
End Function

Print "CompBE64 Tests:"
Print CompBE64(ZeroBE64$, ZeroBE64$)
Print CompBE64(ZeroBE64$, OneBE64$)
Print CompBE64(OneBE64$, ZeroBE64$)
Print CompBE64(OneBE64$, OneBE64$)
Print CompBE64("", ZeroBE64$)
Print CompBE64("", OneBE64$)
Print CompBE64(ZeroBE64$, "")
Print CompBE64(OneBE64$, "")

;**
;* Shift the string left by a number of bits
;*
;* Shift the bits of num$ bits steps to the left
;*
;* @param num$ The number to shift
;* @param bits Number of bits to shift left
;*
;* @return This number, shifted left bits bits
;*/
Function ShlBE64$(num$, bits)
    result$ = ""
    H = bits Shr 3
    L = bits And 7
    For I = 1 To 8
        A = Asc(Mid$(num$, I + H))
        If A < 0 Then A = 0
        B = Asc(Mid$(num$, I + H + 1))
        If B < 0 Then B = 0
        result$ = result$ + Chr$((A Shl L) Or (B Shr (8 - L)))
    Next
    Return result$
End Function

Print "ShlBE64 Tests:"
DumpBE64 ShlBE64$(OneBE64$, 0)
DumpBE64 ShlBE64$(OneBE64$, 1)
DumpBE64 ShlBE64$(OneBE64$, 2)
DumpBE64 ShlBE64$(OneBE64$, 4)
DumpBE64 ShlBE64$(OneBE64$, 8)
DumpBE64 ShlBE64$(OneBE64$, 16)
DumpBE64 ShlBE64$(OneBE64$, 32)
DumpBE64 ShlBE64$(OneBE64$, 63)
DumpBE64 ShlBE64$(OneBE64$, 64)

;**
;* Subtraction on string
;*
;* Difference of num1$ and num2$
;*
;* @param num1$ Initial number
;* @param num2$ Number to subtract
;*
;* @return Difference of num1$ and num2$
;*/
Function SubBE64$(num1$, num2$)
    result$ = ""
    carry = 0
    For I = 8 To 1 Step -1
        A = Asc(Mid$(num1$, I))
        If A < 0 Then A = 0
        B = Asc(Mid$(num2$, I))
        If B < 0 Then B = 0
        result$ = Chr$((A - B - carry) And 255) + result$
        If A > B
           carry = 0
        ElseIf A < B
           carry = 1
        EndIf
    Next
    Return result$
End Function

Print "SubBE64 Tests:"
DumpBE64 SubBE64$(ZeroBE64$, ZeroBE64$)
DumpBE64 SubBE64$(OneBE64$, OneBE64$)
DumpBE64 SubBE64$(OneBE64$, ZeroBE64$)
DumpBE64 SubBE64$(EncodeBE64$(65536), EncodeBE64$(65535))

;**
;* Addition on string
;*
;* Sum of num1$ and num2$
;*
;* @param num1$ Initial number
;* @param num2$ Number to add
;*
;* @return Sum of num1$ and num2$
;*/
Function AddBE64$(num1$, num2$)
    result$ = ""
    carry = 0
    For I = 8 To 1 Step -1
        A = Asc(Mid$(num1$, I))
        If A < 0 Then A = 0
        B = Asc(Mid$(num2$, I))
        If B < 0 Then B = 0
        result$ = Chr$((A + B + carry) And 255) + result$
        If A + B + carry > 255
           carry = 1
        Else
           carry = 0
        EndIf
    Next
    Return result$
End Function

Print "AddBE64 Tests:"
DumpBE64 AddBE64$(ZeroBE64$, ZeroBE64$)
DumpBE64 AddBE64$(OneBE64$, OneBE64$)
DumpBE64 AddBE64$(OneBE64$, ZeroBE64$)
DumpBE64 AddBE64$(EncodeBE64$(65535), EncodeBE64$(65535))
DumpBE64 AddBE64$(EncodeBE64$(65536), EncodeBE64$(65535))

;**
;* Division on string
;*
;* Quotient of num1$ and num2$
;*
;* @fixme Currently does not pass tests
;*
;* @param num1$ Initial number
;* @param num2$ Number to subtract
;*
;* @return Difference of num1$ and num2$
;*/
Function DivBE64(num1$, num2$)
    Result$    = ""
    remainder$ = num1$
    If CompBE64(num2$, "") <> 0
        For lp = 63 To 0 Step -1
            If CompBE64(ShlBE64$(num2$, lp), num1$) <= 0
                num1$   = SubBE64$(num1$, ShlBE64$(num2$, lp))
                Result$ = AddBE64$(Result$, EncodeBE64$(1 Shl lp))
            EndIf
        Next
        remainder$ = num1$
    EndIf
    Return Result$ ;remainder$ also contains remainder
End Function

Print "DivBE64 Tests:"
DumpBE64 DivBE64(ZeroBE64$, OneBE64$)
DumpBE64 DivBE64(OneBE64$, OneBE64$)
DumpBE64 DivBE64(EncodeBE64$(12345), OneBE64$)
DumpBE64 DivBE64(EncodeBE64$(12345), EncodeBE64$(456))

WaitKey
End