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ancp

Help with calculating 8-bit checksum (CRC8)

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Hello all,

please, can someone help me how to calculate checksum file: CRC-8? I am no expert on computing bytes and I tried browse this forum, but found nothing :D Is CRC8 ascii sum of all bytes and multiply of 256? And,... Is there any quick method for this calculation, because I need to calculate a CRC8 checksum for each file in my folder (etimated File size is 10+ MB)? Thanks for any reply or guidance.

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#2 ·  Posted (edited)

Not sure, try this

Dim $avTest[5] = ["Test line 1.", "abcdefghijklmnopqrstuvwxyz01234567890", 0xFEDCBA98, "", StringToBinary("Binary test.")]
$sMsg = ""
For $n = 0 To UBound($avTest) - 1
    $sMsg &= $avTest[$n] & " CRC8 = " & _StringCrc8($avTest[$n]) & @CRLF
Next
MsgBox(64, "StringCrc8 Test", $sMsg)

; =======================================================
; Function  _StringCrc8
; Purpose:  Return the CRC8 checksum of the input value
; Author:   CRC16 example by roby and PsaltyDS at http://www.autoitscript.com/forum/index.php?showtopic=55402&view=findpost&p=420336
;           CRC8 by KaFu derived from CRC16 and a CRC8 table found here http://snippets.dzone.com/tag/crc8
; =======================================================
Func _StringCrc8($value)
    Local $crc = 0x0000, $i = 0
    
    Local $table[256] = [ _
        0x00, 0x07, 0x0e, 0x09, 0x1c, 0x1b, 0x12, 0x15, _ 
        0x38, 0x3f, 0x36, 0x31, 0x24, 0x23, 0x2a, 0x2d, _ 
        0x70, 0x77, 0x7e, 0x79, 0x6c, 0x6b, 0x62, 0x65, _ 
        0x48, 0x4f, 0x46, 0x41, 0x54, 0x53, 0x5a, 0x5d, _ 
        0xe0, 0xe7, 0xee, 0xe9, 0xfc, 0xfb, 0xf2, 0xf5, _ 
        0xd8, 0xdf, 0xd6, 0xd1, 0xc4, 0xc3, 0xca, 0xcd, _ 
        0x90, 0x97, 0x9e, 0x99, 0x8c, 0x8b, 0x82, 0x85, _ 
        0xa8, 0xaf, 0xa6, 0xa1, 0xb4, 0xb3, 0xba, 0xbd, _ 
        0xc7, 0xc0, 0xc9, 0xce, 0xdb, 0xdc, 0xd5, 0xd2, _ 
        0xff, 0xf8, 0xf1, 0xf6, 0xe3, 0xe4, 0xed, 0xea, _ 
        0xb7, 0xb0, 0xb9, 0xbe, 0xab, 0xac, 0xa5, 0xa2, _ 
        0x8f, 0x88, 0x81, 0x86, 0x93, 0x94, 0x9d, 0x9a, _ 
        0x27, 0x20, 0x29, 0x2e, 0x3b, 0x3c, 0x35, 0x32, _ 
        0x1f, 0x18, 0x11, 0x16, 0x03, 0x04, 0x0d, 0x0a, _ 
        0x57, 0x50, 0x59, 0x5e, 0x4b, 0x4c, 0x45, 0x42, _ 
        0x6f, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7d, 0x7a, _ 
        0x89, 0x8e, 0x87, 0x80, 0x95, 0x92, 0x9b, 0x9c, _ 
        0xb1, 0xb6, 0xbf, 0xb8, 0xad, 0xaa, 0xa3, 0xa4, _ 
        0xf9, 0xfe, 0xf7, 0xf0, 0xe5, 0xe2, 0xeb, 0xec, _ 
        0xc1, 0xc6, 0xcf, 0xc8, 0xdd, 0xda, 0xd3, 0xd4, _ 
        0x69, 0x6e, 0x67, 0x60, 0x75, 0x72, 0x7b, 0x7c, _ 
        0x51, 0x56, 0x5f, 0x58, 0x4d, 0x4a, 0x43, 0x44, _ 
        0x19, 0x1e, 0x17, 0x10, 0x05, 0x02, 0x0b, 0x0c, _ 
        0x21, 0x26, 0x2f, 0x28, 0x3d, 0x3a, 0x33, 0x34, _ 
        0x4e, 0x49, 0x40, 0x47, 0x52, 0x55, 0x5c, 0x5b, _ 
        0x76, 0x71, 0x78, 0x7f, 0x6a, 0x6d, 0x64, 0x63, _ 
        0x3e, 0x39, 0x30, 0x37, 0x22, 0x25, 0x2c, 0x2b, _ 
        0x06, 0x01, 0x08, 0x0f, 0x1a, 0x1d, 0x14, 0x13, _ 
        0xae, 0xa9, 0xa0, 0xa7, 0xb2, 0xb5, 0xbc, 0xbb, _ 
        0x96, 0x91, 0x98, 0x9f, 0x8a, 0x8d, 0x84, 0x83, _ 
        0xde, 0xd9, 0xd0, 0xd7, 0xc2, 0xc5, 0xcc, 0xcb, _ 
        0xe6, 0xe1, 0xe8, 0xef, 0xfa, 0xfd, 0xf4, 0xf3 ]

    ConsoleWrite("Debug: $value = " & $value & "  Len = " & StringLen($value) & @LF)
    For $i = 1 To StringLen($value)
        $crc = BitXOR(BitShift($crc, 8), $table[BitAND(BitXOR($crc, Asc(StringMid($value, $i, 1))), 0xFF) ])
    Next
    Return Hex($crc, 4)
EndFunc ;==>_StringCrc8

Derived from this example #420336 by roby and PsaltyDS, add this crc8 table http://snippets.dzone.com/tag/crc8

To get crc8 from a file I think a fileread of the content to a var and then calc crc8 on that var would do.

Edited by KaFu

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#3 ·  Posted (edited)

Many thanks, KaFu for your assistance, but returned value from _StringCrc8() func isn't correct 8-bit CRC. I compare the values with hex editor, which calculates different CRC-8.

I tested this function on the file with size 400kB. My old PC (2.8 GHz Celeron) died after ten minutes :D The second PC (Core Duo 1.7 GHz) returned value after 15 sec, but with wrong value. On this forum I found the 32-bit CRC which works incredibly quickly. Is there a possibility to revise it to CRC8?

Edited by ancp

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