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| − | <html>
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| − | <title>CRC Prefix Calculator</title>
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| − | <script type="text/javascript">
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| − | //<![CDATA[
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| − | function calculateInit () {
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| − | str = document.crcform.hexstring.value.toString();
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| − | var prefix = crc.calculateInitFunc(str);
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| − | document.getElementById("initcrc").textContent =
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| − | prefix.toString(16).toUpperCase().padStart(4, "0");
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| − | }
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| − | var crc = (function() {
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| − | applyCRC = function(crc, value) {
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| − | crc ^= value << 8;
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| − | crc &= 0xffff;
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| − | for (bit = 0; bit < 8; bit++) {
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| − | var olddata = crc & 0x8000;
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| − | crc <<= 1;
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| − | if (olddata) {
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| − | crc ^= 0x1021;
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| − | }
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| − | crc &= 0xffff;
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| − | }
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| − | return crc;
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| − | }
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| − |
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| − | calcCRC = function(pkt, crc) {
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| − | return pkt.reduce(applyCRC, crc);
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| − | }
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| − |
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| − | stringToBytes = function(s){
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| − | return s.split(/([a-fA-F0-9][a-fA-F0-9])/g).filter(p => !!p).map(c => parseInt(c, 16));
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| − | }
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| − |
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| − | bytesToString = function(b) {
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| − | return b.map(c => c.toString(16).padStart(2,"0")).join("");
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| − | }
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| − |
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| − | return {
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| − | calculateInitFunc : function (str) {
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| − | str = str.toUpperCase().replace(/\s/g,"");
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| − | var bytes = stringToBytes(str);
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| − | for (testvalue = 0; testvalue < 65536; testvalue+=1) {
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| − | if (calcCRC(bytes,testvalue) === 0) {
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| − | return testvalue;
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| − | }
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| − | }
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| − | }
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| − | };
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| − | })();
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| − | //]]>
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| − | </script>
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| − | </head>
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| − | <body>
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| − | <h1>CRC Prefix Calculator</h1>
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| − | <p>Enter a string of hex bytes in the box and hit the <b>Find CRC init</b> 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.
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| − | </p>
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| − | <form name="crcform">
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| − | <textarea name="hexstring" rows="5" cols="80">30FFFFFFFFFFFF50CF5DD9E2C0B80065F5D1A483F0FBBC6F01001E6C043B517E90B286
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| − | </textarea>
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| − | <br>
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| − | <label>Initial CRC value (hex):</label>
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| − | <label id="initcrc">5FD6</label>
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| − | <br>
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| − | <input name="submit" type="button" value="Find CRC init" onclick="calculateInit()">
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| − | </form>
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| − |
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| − |
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| − | </body></html>
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