CRC即循环冗余校验码（Cyclic Redundancy Check）：是数据通信领域中最常用的一种差错校验码，其特征是信息字段和校验字段的长度可以任意选定。
1 byte checksum
CRC-16
CRC-16 (Modbus)
CRC-16 (Sick)
CRC-CCITT (XModem)
CRC-CCITT (0xFFFF)
CRC-CCITT (0x1D0F)
CRC-CCITT (Kermit)
CRC-DNP
CRC-32
这里我以CRC-CCITT (XModem) 为例，分别用计算方法与查表法来实现
1.计算法
public static int CRC_XModem(byte[] bytes){
int crc = 0x00; // initial value
int polynomial = 0x1021;
for (int index = 0 ; index< bytes.length; index++) {
byte b = bytes[index];
for (int i = 0; i < 8; i++) {
boolean bit = ((b >> (7-i) & 1) == 1);
boolean c15 = ((crc >> 15 & 1) == 1);
crc <<= 1;
if (c15 ^ bit) crc ^= polynomial;
}
}
crc &= 0xffff;
return crc;
}2.查表法：
static final char TABLE1021[] = { /* CRC1021余式表 */
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 };
public static char getCRC1021(byte b[], int len) {
char crc = 0;
byte hb = 0;
int j = 0;
int index;
while (len-- != 0) {
hb = (byte) (crc / 256); //以8位二进制数的形式暂存CRC的高8位
index = ((hb ^ b[j]) & 0xff); //求得所查索引下标
crc <<= 8; // 左移8位，相当于CRC的低8位乘以
crc ^= (TABLE1021[index]); // 高8位和当前字节相加后再查表求CRC ，再加上以前的CRC
j++;
}
return (crc);
}3.测试方法与结果：
public static void main(String args[]) {
byte[] b = new byte[] {
(byte) 0x2C, (byte) 0x00, (byte) 0xFF, (byte) 0xFE,
(byte) 0xFE, (byte) 0x04, (byte) 0x00, (byte) 0x00,
(byte) 0x00, (byte) 0x00 };
int a = getCRC1021(b, 10);
System.out.println("查表法:" + a);
String str = Integer.toHexString(a).toUpperCase();
System.out.println("十六进制:" + str);
System.out.println("计算法:" + CRC_XModem(b));
System.out.println("十六进制:"
+ Integer.toHexString(CRC_XModem(b)).toUpperCase());
}结果：
