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Calculate two checksums for a hexadecimal string

I have the string "0AAE0000463130004144430000", and I need to calculate the two complement checksums of the hexadecimal bytes that make up the string.

The formula for the sample line above

  • Summarize the values: 0A + AE + 00 + 00 + 46 + 31 + 30 + 00 + 41 + 44 + 43 + 00 + 00 = 27 (discard overflow)
  • Subtract the result from 0x100 = 0xD9

D9 is the correct checksum for this example, but I am having trouble getting two-digit hexadecimal values ​​aligned from a string in C #. My current code is below:

string output = "0AAE0000463130004144430000";
long checksum = 0;
char[] outputBytes = output.TrimStart(':').ToCharArray();

foreach (var outputByte in outputBytes)
{
    checksum += Convert.ToInt32(outputByte);
    checksum = checksum & 0xFF;
}

checksum = 256 - checksum;

However, this sums up the ASCII values, as far as I can tell, and do it for each individual character.

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2 answers

SoapHexBinary System.Runtime.Remoting.Metadata.W3cXsd2001.

soapHexBinary.Value

string hexString = "0AAE0000463130004144430000";
byte[] buf = SoapHexBinary.Parse(hexString).Value;

int chkSum = buf.Aggregate(0, (s, b) => s += b) & 0xff;
chkSum = (0x100 - chkSum) & 0xff;

var str = chkSum.ToString("X2"); // <-- D9
+8

. SubString , int.Parse NumberStyles.AllowHexSpecifier.

string output = "0AAE0000463130004144430000";
int checksum = 0;

// You'll need to add error checking that the string only contains [0-9A-F], 
// is an even number of characters, etc.
for(int i = 0; i < output.length; i+=2)
{
   int value = int.Parse(output.SubString(i, 2), NumberStyles.AllowHexSpecifier);
   checksum = (checksum + value) & 0xFF;
}

checksum = 256 - checksum;
+2

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