Difference between revisions of "Widget:CRCprefix"
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<title>CRC Prefix Calculator</title> | <title>CRC Prefix Calculator</title> | ||
<script type="text/javascript"> | <script type="text/javascript"> | ||
Revision as of 20:01, 21 May 2022
<html> <title>CRC Prefix Calculator</title> <script type="text/javascript"> //<![CDATA[ function calculateInit () {
str = document.crcform.hexstring.value.toString();
var prefix = crc.calculateInitFunc(str);
document.getElementById("initcrc").textContent =
prefix.toString(16).toUpperCase().padStart(4, "0");
}
var crc = (function() {
applyCRC = function(crc, value) {
crc ^= value << 8;
crc &= 0xffff;
for (bit = 0; bit < 8; bit++) {
var olddata = crc & 0x8000;
crc <<= 1;
if (olddata) {
crc ^= 0x1021;
}
crc &= 0xffff;
}
return crc;
}
calcCRC = function(pkt, crc) {
return pkt.reduce(applyCRC, crc);
}
stringToBytes = function(s){
return s.split(/([a-fA-F0-9][a-fA-F0-9])/g).filter(p => !!p).map(c => parseInt(c, 16));
}
bytesToString = function(b) {
return b.map(c => c.toString(16).padStart(2,"0")).join("");
}
return {
calculateInitFunc : function (str) {
str = str.toUpperCase().replace(/\s/g,"");
var bytes = stringToBytes(str);
for (testvalue = 0; testvalue < 65536; testvalue+=1) {
if (calcCRC(bytes,testvalue) === 0) {
return testvalue;
}
}
}
};
})(); //]]> </script> </head> <body>
CRC Prefix Calculator
Enter a string of hex bytes in the box and hit the Find CRC init button searches for the initial CRC value which would make the calculated CRC equal to zero. It uses the 0x1021 polynomial value. If it cannot find such a value, it will leave the value unchanged.
<form name="crcform">
<textarea name="hexstring" rows="5" cols="80">30FFFFFFFFFFFF50CF5DD9E2C0B80065F5D1A483F0FBBC6F01001E6C043B517E90B286
</textarea>
<label>Initial CRC value (hex):</label>
<label id="initcrc">5FD6</label>
<input name="submit" type="button" value="Find CRC init" onclick="calculateInit()">
</form>
</body></html>
