用Java中的多项式x ^ 16 + x ^ 12 + x ^ 5 +1计算CCITT标准CRC [英] Calculation of CCITT standard CRC with polynomial x^16 + x^12 + x^5 + 1 in Java
问题描述
我需要Java多项式x ^ 16 + x ^ 12 + x ^ 5 +1(0x1081)来计算CCITT标准CRC的帮助.我在互联网上尝试了许多示例,但每个示例都返回了示例中其他值以外的其他值.
I need help with calculating of CCITT standard CRC with polynomial x^16 + x^12 + x^5 + 1 (0x1081) in Java. I have tried many examples on the internet but every one of them returns other values than the ones in the example.
例如,对于此数组[0xFC] [05] [11],结果必须为[27] [56].
For example for this array [0xFC] [05] [11] the result needs to be [27] [56].
使用此代码:
public static void main(String[] args) {
byte[] array = new byte[3];
array[0] = (byte) 0xFC;
array[1] = (byte) 0x05;
array[2] = (byte) 0x11;
// array[3] = (byte) 0x00;
// array[4] = (byte) 0x00;
System.out.println(Integer.toHexString(crc16(array)));
}
private static final int POLYNOMIAL = 0x1081;
private static final int PRESET_VALUE = 0xFFFF;
public static int crc16(byte[] data) {
int current_crc_value = PRESET_VALUE;
for (int i = 0; i < data.length; i++) {
current_crc_value ^= data[i] & 0xFF;
for (int j = 0; j < 8; j++) {
if ((current_crc_value & 1) != 0) {
current_crc_value = (current_crc_value >>> 1) ^ POLYNOMIAL;
} else {
current_crc_value = current_crc_value >>> 1;
}
}
}
current_crc_value = ~current_crc_value;
return current_crc_value & 0xFFFF;
}
我得到的结果是 FA DE
,而不是[27] [56]
I get result FA DE
not [27] [56]
使用此代码:
public static void main(String[] args) {
int crc = 0x0000;
int polynomial = 0x1081;
// byte[] testBytes = "123456789".getBytes("ASCII");
// byte[] array = args[0].getBytes();
byte[] array = new byte[3];
array[0] = (byte) 0xFC;
array[1] = (byte) 0x05;
array[2] = (byte) 0x11;
for (byte b : array) {
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;
System.out.println("CRC16-CCITT = " + Integer.toHexString(crc));
}
我得到了这个 CRC16-CCITT = 8dca
使用此代码:
private final int polynomial = 0x1081;
private int[] table = new int[256];
public int ComputeChecksum(int[] bytes) {
int crc = 0xffff;
for (int i = 0; i < bytes.length; ++i) {
int index = (crc ^ bytes[i]) % 256;
crc = (crc >> 8) ^ table[index];
}
return crc;
}
public CRC162() {
int value;
int temp;
for (int i = 0; i < table.length; ++i) {
value = 0;
temp = i;
for (byte j = 0; j < 8; ++j) {
if (((value ^ temp) & 0x0001) != 0) {
value = (value >> 1) ^ polynomial;
} else {
value >>= 1;
}
temp >>= 1;
}
table[i] = value;
}
}
public static void main(String[] args) {
CRC162 c = new CRC162();
int[] arr = new int[]{0xFC, 0x05, 0x11};
System.out.println(Integer.toHexString(c.ComputeChecksum(arr)));
}
我得到了这个 521
希望有人可以帮助我.与使用ID003协议的设备进行通讯时,我需要此.
Hope someone can help me. I need this for communication with device using ID003 protocol.
在 http://www.lammertbies.nl/comm/info/上使用此在线计算器输入FC0511的crc-calculation.html 我直接从CRC-CCITT(Kermit)得到0x2756.
Using this online calculator at http://www.lammertbies.nl/comm/info/crc-calculation.html for input FC0511 i get 0x2756 right from CRC-CCITT (Kermit).
推荐答案
这是Kermit CRC的另一个版本.这是 http://www.lammertbies中C代码的直接翻译.nl/comm/info/crc-calculation.html .优化是在类加载时预先计算了任何字节的CRC值表,因此其余的CRC计算要简单得多.
Here is another version of the Kermit CRC. This one is a direct translation from the C codes in http://www.lammertbies.nl/comm/info/crc-calculation.html. The optimisation is that a table of CRC value for any byte is pre-computed at class loading time, and so the remaining of CRC computations is much simpler.
public class Crc {
private static final int POLYNOMIAL = 0x8408;
private static final int PRESET = 0;
static private int[] tab;
static {
tab = new int[256];
for (int i = 0; i < 256; i++) {
tab[i] = initial((byte) i);
}
}
private static int initial(byte c) {
int crc = 0;
for (int j = 0; j < 8; j++) {
if (((crc ^ c) & 1) == 1) {
crc = ((crc >> 1) ^ POLYNOMIAL);
} else {
crc = (crc >> 1);
}
c = (byte) (c >> 1);
}
return crc;
}
private static int update_crc(int crc, byte c) {
int cc = (0xff & c);
int tmp = (crc ^ cc);
crc = (crc >> 8) ^ tab[tmp & 0xff];
return crc;
}
private static int swab(int n) {
return (((n & 0xFF00) >> 8) + ((n & 0xFF) << 8));
}
public static int crc(String str) {
return crcb(str.getBytes());
}
public static int crcb(byte... i) {
int crc = PRESET;
for (byte c : i) {
crc = update_crc(crc, c);
}
return swab(crc);
}
public static void main(String[] args) {
int crc = Crc.crcb((byte) 0xFC, (byte) 5, (byte) 0x11);
System.out.println(Integer.toHexString(crc));
crc = Crc.crc("123456789");
System.out.println(Integer.toHexString(crc));
}
}
输出符合预期:
2756
8921
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