(Pardon the ignorance) CRC

[PRIVATE1]

Hey ,

Well What I'm trying to figure out is how to the crc value of a string . As for the ignorance , If I knew exactly what crc was I might have been able to do it along . I know I want it for file transfer .

Thanks

[]P

[paulw]

Cyclic Redundancy Check

It is a way of using bit values to ensure that the string transmitted is what is received. If individual bits are transposed in transmission the CRC will reveal this. I believe that ther are several schemes but I don't know the implementation details. I could find them out tho' if it is important.

P.

Public Function CalcChecksum(S As String) As Byte
' =====================================================================================
' ===                                                    Comments by CommentMaker   ===
' =====================================================================================
'
' Function    : CalcChecksum
' Date/Time   : wednesday 20-sep-2000 / 09:45
' By          : Rob Janssen
'
' Versie      : 1.0
'
' Description:
'
' Calculates a string-checksum (CRC):
'
' 1) Put 1st byte of the string in a Checksum-byte
' 2) Clear bit 7 of the resultaat
' 3) Set bit 6 of the resultaat
' 4) Add the result to the next byte (=char) of the string
' 5) Repeat steps 2-4 till the end of the string
'
'
' Parameters  :
'
'   S                   - [Required] String          "To-be-checksummed"-string
'
' Return      : Byte
'
' Revisions   :
'
' =====================================================================================
' ===                                                    Comments by CommentMaker   ===
' =====================================================================================
    
    Dim chk As Byte ' Checksum
    Dim T As Long   ' Char-pointer...
    
    ' Step 1
    chk = Asc(Mid(S, 1, 2))    ' Get 1st Char
    
    T = 1
    While T < Len(S)
       
        ' Step 2
        chk = chk And 127   ' Bitwise operation. Clear bit 7 (127 -> 01111111)
        
        ' Step 3
        chk = chk Or 64     ' Bitwise operation. Set bit 6 (64 -> 01000000)
        
        T = T + 1
        
        ' Step 4
        chk = Asc(Mid(S, T, 1)) + chk
    Wend
    
    CalcChecksum = chk
End Function

usage:

   Dim CRC as Byte
   
   CRC=CalcChecksum("Hello World")