将CRC8从C翻译成Java
我收到一段C代码,它计算字节数组的CRC8值。 我需要把它翻译成Java 这里是C代码:将CRC8从C翻译成Java,java,c,crc,Java,C,Crc,我收到一段C代码,它计算字节数组的CRC8值。 我需要把它翻译成Java 这里是C代码: CRC_POLYNOM = 0x9c; CRC_PRESET = 0xFF; unsigned int CRC = CRC_PRESET; for (i = 0; i < Len; i++) { crc ^= FRAME[i]; for (j = 0; j < 8; j++) { if (crc & 0x01) crc = (crc >>
CRC_POLYNOM = 0x9c;
CRC_PRESET = 0xFF;
unsigned int CRC = CRC_PRESET;
for (i = 0; i < Len; i++)
{
crc ^= FRAME[i];
for (j = 0; j < 8; j++)
{
if (crc & 0x01)
crc = (crc >> 1) ^ CRC_POLYNOM;
else
crc = (crc >> 1);
}
}
C代码返回29,而我的Java代码返回44。
我做错了什么
我认为这是因为Java的纯签名数据类型,所以我如何修复它
if (crc & 0x01)
此测试是否设置了最低位
if ((crc & 0x01) == 0)
这将测试底部钻头是否清晰
您还应该在Java代码中使用无符号右移(即在两个位置使用>>
而不是>
),并在返回结果之前使用0xff
屏蔽结果
编辑最后您需要更改:
crc ^= b[i];
为此:
crc ^= b[i] & 0xff;
但是,您应该真正抛弃它,并查找表驱动方法。速度是这个的八倍
编辑2表驱动版本,经过修订以实现java.util.zip.Checksum:
public class CRC8 implements Checksum
{
private final short init;
private final short[] crcTable = new short[256];
private short value;
/**
* Construct a CRC8 specifying the polynomial and initial value.
* @param polynomial Polynomial, typically one of the POLYNOMIAL_* constants.
* @param init Initial value, typically either 0xff or zero.
*/
public CRC8(int polynomial, short init)
{
this.value = this.init = init;
for (int dividend = 0; dividend < 256; dividend++)
{
int remainder = dividend ;//<< 8;
for (int bit = 0; bit < 8; ++bit)
if ((remainder & 0x01) != 0)
remainder = (remainder >>> 1) ^ polynomial;
else
remainder >>>= 1;
crcTable[dividend] = (short)remainder;
}
}
@Override
public void update(byte[] buffer, int offset, int len)
{
for (int i = 0; i < len; i++)
{
int data = buffer[offset+i] ^ value;
value = (short)(crcTable[data & 0xff] ^ (value << 8));
}
}
/**
* Updates the current checksum with the specified array of bytes.
* Equivalent to calling <code>update(buffer, 0, buffer.length)</code>.
* @param buffer the byte array to update the checksum with
*/
public void update(byte[] buffer)
{
update(buffer, 0, buffer.length);
}
@Override
public void update(int b)
{
update(new byte[]{(byte)b}, 0, 1);
}
@Override
public long getValue()
{
return value & 0xff;
}
@Override
public void reset()
{
value = init;
}
public static void main(String[] args)
{
final int CRC_POLYNOM = 0x9C;
final byte CRC_INITIAL = (byte)0xFF;
final byte[] data = {1, 56, -23, 3, 0, 19, 0, 0, 2, 0, 3, 13, 8, -34, 7, 9, 42, 18, 26, -5, 54, 11, -94, -46, -128, 4, 48, 52, 0, 0, 0, 0, 0, 0, 0, 0, 4, 1, 1, -32, -80, 0, 98, -5, 71, 0, 64, 0, 0, 0, 0, -116, 1, 104, 2};
CRC8 crc8 = new CRC8(CRC_POLYNOM, CRC_INITIAL);
crc8.update(data,0,data.length);
System.out.println("Test successful:\t"+(crc8.getValue() == 29));
}
}
您的“^”实际上已经像箭头一样指向错误所在的部分
相当于
if (crc & 0x01)
在Java中是(因为Java需要if中的布尔表达式)
或
我为您的问题创建了一个完整/独立的C程序:
#include <stdio.h>
#define CRC_POLYNOM 0x9c
#define CRC_PRESET 0xFF
int main() {
unsigned int crc = CRC_PRESET;
unsigned char FRAME[] = {1, 56, -23, 3, 0, 19, 0, 0, 2, 0, 3, 13, 8, -34, 7, 9, 42, 18, 26, -5, 54, 11, -94, -46, -128, 4, 48, 52, 0, 0, 0, 0, 0, 0, 0, 0, 4, 1, 1, -32, -80, 0, 98, -5, 71, 0, 64, 0, 0, 0, 0, -116, 1, 104, 2};
for(int i = 0; i < sizeof(FRAME); i++) {
crc ^= FRAME[i];
for(int j = 0; j < 8; j++) {
if(crc & 0x01) {
crc = (crc >> 1) ^ CRC_POLYNOM;
} else {
crc = (crc >> 1);
}
}
}
printf("%u\n", crc);
return 0;
}
#包括
#定义CRC_多项式0x9c
#定义CRC_预设0xFF
int main(){
无符号整数crc=crc\U预置;
无符号字符帧[]={1,56,-23,3,0,19,0,0,2,0,3,13,8,-34,7,9,42,18,26,-5,54,11,-94,-46,-128,4,48,52,0,0,0,0,0,0,0,0,0,0,0,0,1,1,-32,-80,0,98,-5,71,0,64,0,0,0,0,0,0,0,0,0,0,-116,1,104,2};
对于(int i=0;i>1)^crc多项式;
}否则{
crc=(crc>>1);
}
}
}
printf(“%u\n”,crc);
返回0;
}
以下是自动创建的等效Java代码:
软件包演示;
公共类翻译{
公共最终静态整数CRC_多项式=0x9c;
公共最终静态整数CRC_预设=0xFF;
公共静态void main(字符串[]args){
int crc_=crc_预设值;
字节[]帧_={1,56,-23,3,0,19,0,0,2,0,3,13,8,-34,7,9,42,18,26,-5,54,11,-94,-46,-128,4,48,52,0,0,0,0,0,0,0,0,0,0,0,0,1,1,-32,-80,0,98,-5,71,0,64,0,0,0,0,0,0,0,0,0,-116,1,104,2};
对于(int i=0;i>>1);
}
}
}
System.out.println(Integer.toUnsignedString(crc_));
}
}
谢谢你的回答。但现在它返回47而不是44。我在回答中提到的所有更正?在这四个地方?“crc”在C代码中是否初始化为crc_预置?是的,我猜是>>>而不是EJPs同步应答中的>>。这里的语义不同,因为java不像C那样具有“未签名”类型。它有时也会在使用较小的字体时进行注释。现在,当我切换到>>>并用0xff@AlexanderCiesielski如果您对我的答案发表评论,请在我的答案下发表评论。If((crc&0x01)==0x01)crc=((crc>>1)和0xff)^crc\u POLYNOM;else crc=(crc>>1)&0xff;}返回crc代码>我用0xff屏蔽了三次右移。现在返回75。@AlexanderCiesielski继续观察,我会发布表代码,但今晚可能不会,现在是我的时间10:30。将“更新(int)”替换为:public void update(int b){update(ByteBuffer.allocate(Integer.BYTES).putin(b.array(),0,Integer.BYTES);}
if (crc & 0x01)
if ((crc & 0x01) != 0)
if ((crc & 0x01) == 0x01)
#include <stdio.h>
#define CRC_POLYNOM 0x9c
#define CRC_PRESET 0xFF
int main() {
unsigned int crc = CRC_PRESET;
unsigned char FRAME[] = {1, 56, -23, 3, 0, 19, 0, 0, 2, 0, 3, 13, 8, -34, 7, 9, 42, 18, 26, -5, 54, 11, -94, -46, -128, 4, 48, 52, 0, 0, 0, 0, 0, 0, 0, 0, 4, 1, 1, -32, -80, 0, 98, -5, 71, 0, 64, 0, 0, 0, 0, -116, 1, 104, 2};
for(int i = 0; i < sizeof(FRAME); i++) {
crc ^= FRAME[i];
for(int j = 0; j < 8; j++) {
if(crc & 0x01) {
crc = (crc >> 1) ^ CRC_POLYNOM;
} else {
crc = (crc >> 1);
}
}
}
printf("%u\n", crc);
return 0;
}
package demo;
public class DemoTranslation {
public final static int CRC_POLYNOM = 0x9c;
public final static int CRC_PRESET = 0xFF;
public static void main(String[] args) {
int crc_U = CRC_PRESET;
byte[] frame_U = {1, 56, -23, 3, 0, 19, 0, 0, 2, 0, 3, 13, 8, -34, 7, 9, 42, 18, 26, -5, 54, 11, -94, -46, -128, 4, 48, 52, 0, 0, 0, 0, 0, 0, 0, 0, 4, 1, 1, -32, -80, 0, 98, -5, 71, 0, 64, 0, 0, 0, 0, -116, 1, 104, 2};
for(int i = 0; i < frame_U.length; i++) {
crc_U ^= Byte.toUnsignedInt(frame_U[i]);
for(int j = 0; j < 8; j++) {
if((crc_U & 0x01) != 0) {
crc_U = (crc_U >>> 1) ^ CRC_POLYNOM;
} else {
crc_U = (crc_U >>> 1);
}
}
}
System.out.println(Integer.toUnsignedString(crc_U));
}
}