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crc16-ccitt
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README.markdown
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crc.js
/*
* This doesn't work, poor attempt at porting the C code.
*/
function crc16CCITT(buf, seed)
{
var crc = Number.isNaN(seed) ? 0xFFFF : seed;
for (var i = 0, len = buf.length; i < len; ++i)
{
crc = (((crc >> 8) & 0xFF) | ((crc << 8) & 0xFFFF));
crc ^= buf[i];
crc ^= ((crc >> 4) & 0xFF);
crc ^= ((((crc << 8) & 0xFFFF) << 4) & 0xFFFF);
crc ^= (((((crc & 0xFF) << 4) & 0xFFFF) << 1) & 0xFFFF);
}
return crc;
}
/*
* This one works, from http://automationwiki.com/index.php?title=CRC-16-CCITT
*/
var crc_table = [
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5,
0x60c6, 0x70e7, 0x8108, 0x9129, 0xa14a, 0xb16b,
0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x0210,
0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c,
0xf3ff, 0xe3de, 0x2462, 0x3443, 0x0420, 0x1401,
0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b,
0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6,
0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719, 0x8738,
0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 0x48c4, 0x58e5,
0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969,
0xa90a, 0xb92b, 0x5af5, 0x4ad4, 0x7ab7, 0x6a96,
0x1a71, 0x0a50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc,
0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03,
0x0c60, 0x1c41, 0xedae, 0xfd8f, 0xcdec, 0xddcd,
0xad2a, 0xbd0b, 0x8d68, 0x9d49, 0x7e97, 0x6eb6,
0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a,
0x9f59, 0x8f78, 0x9188, 0x81a9, 0xb1ca, 0xa1eb,
0xd10c, 0xc12d, 0xf14e, 0xe16f, 0x1080, 0x00a1,
0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c,
0xe37f, 0xf35e, 0x02b1, 0x1290, 0x22f3, 0x32d2,
0x4235, 0x5214, 0x6277, 0x7256, 0xb5ea, 0xa5cb,
0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447,
0x5424, 0x4405, 0xa7db, 0xb7fa, 0x8799, 0x97b8,
0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2,
0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9,
0xb98a, 0xa9ab, 0x5844, 0x4865, 0x7806, 0x6827,
0x18c0, 0x08e1, 0x3882, 0x28a3, 0xcb7d, 0xdb5c,
0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0,
0x2ab3, 0x3a92, 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d,
0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 0x7c26, 0x6c07,
0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba,
0x8fd9, 0x9ff8, 0x6e17, 0x7e36, 0x4e55, 0x5e74,
0x2e93, 0x3eb2, 0x0ed1, 0x1ef0
];
function crcCCITT (input, seed) {
var result = seed;
var temp;
for (var i = 0, len = input.length; i < len; ++i) {
temp = (input[i] ^ (result >> 8)) & 0xFF;
result = crc_table[temp] ^ (result << 8);
}
return result;
}
if (!module.parent) {
var input = new Buffer( [ 0x02, 0x06, 0x06, 0x03 ] );
var output = crc16CCITT(input);
var o = new Buffer([output >> 8, output & 0xFF]);
console.log('output:', output, o.toString('hex'));
var c = new Buffer([0x41, 0xCD]);
console.log("(correct is)", 0x41CD, c.toString('hex'));
console.log('attempt 2');
output = crcCCITT(input, 0xFFFF);
o = new Buffer([output >> 8, output & 0xFF]);
console.log('output:', output, o.toString('hex'));
console.log("(correct is)", 0x41CD, c.toString('hex'));
}
Raw
crc_example.c
/* From Asante Porter guide
*/
#include <stdio.h>
unsigned short crc_calculate_crc(
unsigned short initial_crc,
const unsigned char *buffer,
unsigned short length) {
unsigned short index = 0;
unsigned short crc = initial_crc;
if (buffer != NULL) {
for (index = 0; index < length; index++) {
crc = (unsigned short)((unsigned char)(crc >> 8) | (unsigned short)(crc << 8));
crc ^= buffer[index];
crc ^= (unsigned char)(crc & 0xFF) >> 4;
crc ^= (unsigned short)((unsigned short)(crc << 8) << 4);
crc ^= (unsigned short)((unsigned short)((crc & 0xFF) << 4) << 1);
}
}
return (crc);
}
void main ( ) {
unsigned char test_crc[4] = { 0x02, 0x06, 0x06, 0x03 };
unsigned short crc = crc_calculate_crc( 0xffff, test_crc, 4);
printf("result: %#010x\n", crc);
printf("hex of 0x41CD: %#010x\n", 0x02060603);
printf("hex of 0x41CD: %#010x\n", 0x41);
printf("hex of 0x41CD: %#010x\n", 0xCD);
printf("hex of 0x41CD: %#010x\n", 0x41CD);
}
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