Adding progress bar for CRC32 checksum

johnjsm

Hi, I have a public function that generates a CRC32 checksum of a file. What I am looking to add to it is a progress bar that progresses as the checksum is created. CRC32 Function

Public Function GetCrc32(ByRef stream As System.IO.Stream) As Integer

    Dim crc32Result As Integer
    crc32Result = &HFFFFFFFF

    Dim buffer(BUFFER\_SIZE) As Byte
    Dim readSize As Integer = BUFFER\_SIZE

    Dim count As Integer = stream.Read(buffer, 0, readSize)
    Dim i As Integer
    Dim iLookup As Integer
    Dim tot As Integer = 0
    Do While (count > 0)
        For i = 0 To count - 1
            iLookup = (crc32Result And &HFF) Xor buffer(i)
            crc32Result = ((crc32Result And &HFFFFFF00) \\ &H100) And &HFFFFFF   ' nasty shr 8 with vb :/
            crc32Result = crc32Result Xor crc32Table(iLookup)
        Next i
        count = stream.Read(buffer, 0, readSize)
    Loop

    GetCrc32 = Not (crc32Result)

End Function

the function is then called when I click on a button

Dim f As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, 8192)
crc = c32.GetCrc32(f)
lblCRC32.Text = Hex(crc)

How do I add a progress bar to work with the function and display the actual progress. Thanks J

MicroVirus

What you do is you get the file length (stream.Length) and then you divide the current amount of bytes processed by this value. If you multiply this fraction by 100 then you get the percent complete. All you have to do then is add a progress bar to your form, set its Min to 0, Max to 100, at the start of GetCrc32 set its Value to 0 and then after every iteration you set the progressbar Value to the percent you calculated. On a final note: you might want to do this calculating and updating the progress bar only every N iterations rather than each to avoid slowing down the function, where N is some reasonable value, like 512 or 1024 (after half and 1 KiB reads respectively).

johnjsm

Thank you for your answer but how do I know how many bytes are processed

DaveAuld

Edit: sorry ignore last response, didn't read the question properly...... Anyway, You know the file length from the Stream.length as per the previous message. You also know how my bytes are being read on each iteration on the buffer. You add a totaliser, and with each byte read create the total read so far, then its simply: (total read so far / total length) * 100

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MicroVirus

DaveAuld is correct. Also, the stream.Position gives how many bytes you've read in this case.

johnjsm

Cool. Thanks guys for the help