• Home
 · 
• Math/Dates
 · 
• CRC32(Cyclic Redundancy Check)

CRC32(Cyclic Redundancy Check)

Take a string and calculate a Number that only that String has! Pretty Fast and can do files with a little editing of the code! This is a very well written out code and is pretty simple if you know most of the Visual Basic Commands! Thank You and please Visit https://vbcode.8m.com

Inputs
String

Assumes
The basics of Math and the Commands For Visual Basic

Returns
32-Bit CRC Code of the inputed String

Side Effects
None That i know of

Rate CRC32(Cyclic Redundancy Check)

• 1
• 2
• 3
• 4
• 5

(5(5 Vote))

ption Explicit
Option Compare Text
'// Then declare this array variable Crc32Table
Private Crc32Table(255) As Long
'// Then all we have to do is writing public functions like these...
Public Function InitCrc32(Optional ByVal Seed As Long = &HEDB88320, Optional ByVal Precondition As Long = &HFFFFFFFF) As Long
 '// Declare counter variable iBytes, counter variable iBits, value variables lCrc32 and lTempCrc32
 Dim iBytes As Integer, iBits As Integer, lCrc32 As Long, lTempCrc32 As Long
 '// Turn on error trapping
 On Error Resume Next
 '// Iterate 256 times
 For iBytes = 0 To 255
  '// Initiate lCrc32 to counter variable
  lCrc32 = iBytes
  '// Now iterate through each bit in counter byte
  For iBits = 0 To 7
   '// Right shift unsigned long 1 bit
   lTempCrc32 = lCrc32 And &HFFFFFFFE
   lTempCrc32 = lTempCrc32 \ &H2
   lTempCrc32 = lTempCrc32 And &H7FFFFFFF
   '// Now check if temporary is less than zero and then mix Crc32 checksum with Seed value
   If (lCrc32 And &H1) <> 0 Then
   lCrc32 = lTempCrc32 Xor Seed
   Else
   lCrc32 = lTempCrc32
   End If
  Next
  '// Put Crc32 checksum value in the holding array
  Crc32Table(iBytes) = lCrc32
 Next
 '// After this is done, set function value to the precondition value
 InitCrc32 = Precondition
End Function
'// The function above is the initializing function, now we have to write the computation function
Public Function AddCrc32(ByVal Item As String, ByVal Crc32 As Long) As Long
 '// Declare following variables
 Dim bCharValue As Byte, iCounter As Integer, lIndex As Long
 Dim lAccValue As Long, lTableValue As Long
 '// Turn on error trapping
 On Error Resume Next
 '// Iterate through the string that is to be checksum-computed
 For iCounter = 1 To Len(Item)
  '// Get ASCII value for the current character
  bCharValue = Asc(Mid$(Item, iCounter, 1))
  '// Right shift an Unsigned Long 8 bits
  lAccValue = Crc32 And &HFFFFFF00
  lAccValue = lAccValue \ &H100
  lAccValue = lAccValue And &HFFFFFF
  '// Now select the right adding value from the holding table
  lIndex = Crc32 And &HFF
  lIndex = lIndex Xor bCharValue
  lTableValue = Crc32Table(lIndex)
  '// Then mix new Crc32 value with previous accumulated Crc32 value
  Crc32 = lAccValue Xor lTableValue
 Next
 '// Set function value the the new Crc32 checksum
 AddCrc32 = Crc32
End Function
'// At last, we have to write a function so that we can get the Crc32 checksum value at any time
Public Function GetCrc32(ByVal Crc32 As Long) As Long
 '// Turn on error trapping
 On Error Resume Next
 '// Set function to the current Crc32 value
 GetCrc32 = Crc32 Xor &HFFFFFFFF
End Function
'// To Test the Routines Above...
Public Sub Main()
 Dim lCrc32Value As Long
 On Error Resume Next
 lCrc32Value = InitCrc32()
 lCrc32Value = AddCrc32("This is the original message!", lCrc32Value)
 Debug.Print Hex$(GetCrc32(lCrc32Value))
End Sub
'// This is the command that you would use to compute your own string
Public Function Compute(ToGet as string)as String
 Dim lCrc32Value As Long
 On Error Resume Next
 lCrc32Value = InitCrc32()
 lCrc32Value = AddCrc32(ToGet, lCrc32Value)
 Compute = Hex$(GetCrc32(lCrc32Value))
End Sub