扩展以下问题
Converting crc code from C to Java yields unexpected results
我正在尝试将C代码转换为Java并获得意外结果
C代码如下
/// swap endianess
static inline uint32_t swap(uint32_t x)
{
return (x >> 24) |
((x >> 8) & 0x0000FF00) |
((x << 8) & 0x00FF0000) |
(x << 24);
}
/// look-up table, already declared above
const uint32_t Crc32Lookup[8][256] =
{
{ 0x00000000,0x77073096,0xEE0E612C,0x990951BA,0x076DC419,0x706AF48F,0xE963A535,0x9E6495A3,
0x0EDB8832,0x79DCB8A4,0xE0D5E91E,0x97D2D988,0x09B64C2B,0x7EB17CBD,0xE7B82D07,0x90BF1D91,
0x1DB71064,0x6AB020F2,0xF3B97148,0x84BE41DE,0x1ADAD47D,0x6DDDE4EB,0xF4D4B551,0x83D385C7,
0x136C9856,0x646BA8C0,0xFD62F97A,0x8A65C9EC,0x14015C4F,0x63066CD9,0xFA0F3D63,0x8D080DF5,
0x3B6E20C8,0x4C69105E,0xD56041E4,0xA2677172,0x3C03E4D1,0x4B04D447,0xD20D85FD,0xA50AB56B,
0x35B5A8FA,0x42B2986C,0xDBBBC9D6,0xACBCF940,0x32D86CE3,0x45DF5C75,0xDCD60DCF,0xABD13D59,
0x26D930AC,0x51DE003A,0xC8D75180,0xBFD06116,0x21B4F4B5,0x56B3C423,0xCFBA9599,0xB8BDA50F,
0x2802B89E,0x5F058808,0xC60CD9B2,0xB10BE924,0x2F6F7C87,0x58684C11,0xC1611DAB,0xB6662D3D,
0x76DC4190,0x01DB7106,0x98D220BC,0xEFD5102A,0x71B18589,0x06B6B51F,0x9FBFE4A5,0xE8B8D433,
0x7807C9A2,0x0F00F934,0x9609A88E,0xE10E9818,0x7F6A0DBB,0x086D3D2D,0x91646C97,0xE6635C01,
0x6B6B51F4,0x1C6C6162,0x856530D8,0xF262004E,0x6C0695ED,0x1B01A57B,0x8208F4C1,0xF50FC457,
0x65B0D9C6,0x12B7E950,0x8BBEB8EA,0xFCB9887C,0x62DD1DDF,0x15DA2D49,0x8CD37CF3,0xFBD44C65,
0x4DB26158,0x3AB551CE,0xA3BC0074,0xD4BB30E2,0x4ADFA541,0x3DD895D7,0xA4D1C46D,0xD3D6F4FB,
0x4369E96A,0x346ED9FC,0xAD678846,0xDA60B8D0,0x44042D73,0x33031DE5,0xAA0A4C5F,0xDD0D7CC9,
0x5005713C,0x270241AA,0xBE0B1010,0xC90C2086,0x5768B525,0x206F85B3,0xB966D409,0xCE61E49F,
0x5EDEF90E,0x29D9C998,0xB0D09822,0xC7D7A8B4,0x59B33D17,0x2EB40D81,0xB7BD5C3B,0xC0BA6CAD,
0xEDB88320,0x9ABFB3B6,0x03B6E20C,0x74B1D29A,0xEAD54739,0x9DD277AF,0x04DB2615,0x73DC1683,
0xE3630B12,0x94643B84,0x0D6D6A3E,0x7A6A5AA8,0xE40ECF0B,0x9309FF9D,0x0A00AE27,0x7D079EB1,
0xF00F9344,0x8708A3D2,0x1E01F268,0x6906C2FE,0xF762575D,0x806567CB,0x196C3671,0x6E6B06E7,
0xFED41B76,0x89D32BE0,0x10DA7A5A,0x67DD4ACC,0xF9B9DF6F,0x8EBEEFF9,0x17B7BE43,0x60B08ED5,
0xD6D6A3E8,0xA1D1937E,0x38D8C2C4,0x4FDFF252,0xD1BB67F1,0xA6BC5767,0x3FB506DD,0x48B2364B,
0xD80D2BDA,0xAF0A1B4C,0x36034AF6,0x41047A60,0xDF60EFC3,0xA867DF55,0x316E8EEF,0x4669BE79,
0xCB61B38C,0xBC66831A,0x256FD2A0,0x5268E236,0xCC0C7795,0xBB0B4703,0x220216B9,0x5505262F,
0xC5BA3BBE,0xB2BD0B28,0x2BB45A92,0x5CB36A04,0xC2D7FFA7,0xB5D0CF31,0x2CD99E8B,0x5BDEAE1D,
0x9B64C2B0,0xEC63F226,0x756AA39C,0x026D930A,0x9C0906A9,0xEB0E363F,0x72076785,0x05005713,
0x95BF4A82,0xE2B87A14,0x7BB12BAE,0x0CB61B38,0x92D28E9B,0xE5D5BE0D,0x7CDCEFB7,0x0BDBDF21,
0x86D3D2D4,0xF1D4E242,0x68DDB3F8,0x1FDA836E,0x81BE16CD,0xF6B9265B,0x6FB077E1,0x18B74777,
0x88085AE6,0xFF0F6A70,0x66063BCA,0x11010B5C,0x8F659EFF,0xF862AE69,0x616BFFD3,0x166CCF45,
0xA00AE278,0xD70DD2EE,0x4E048354,0x3903B3C2,0xA7672661,0xD06016F7,0x4969474D,0x3E6E77DB,
0xAED16A4A,0xD9D65ADC,0x40DF0B66,0x37D83BF0,0xA9BCAE53,0xDEBB9EC5,0x47B2CF7F,0x30B5FFE9,
0xBDBDF21C,0xCABAC28A,0x53B39330,0x24B4A3A6,0xBAD03605,0xCDD70693,0x54DE5729,0x23D967BF,
0xB3667A2E,0xC4614AB8,0x5D681B02,0x2A6F2B94,0xB40BBE37,0xC30C8EA1,0x5A05DF1B,0x2D02EF8D
},
.....
};
/// compute CRC32 (Slicing-by-4 algorithm)
uint32_t Crc32FourBytes(const void* data, size_t length, uint32_t previousCrc32 = 0)
{
uint32_t crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF
const uint32_t* current = (const uint32_t*) data;
// process four bytes at once (Slicing-by-4)
while (length >= 4)
{
printf("Here\n");
#if __BYTE_ORDER == __BIG_ENDIAN
printf("BIG ENDIAN\n");
uint32_t one = *current++ ^ swap(crc);
printf("one is %d\n", (int32_t)one);
crc = Crc32Lookup[0][ one & 0xFF] ^
Crc32Lookup[1][(one>> 8) & 0xFF] ^
Crc32Lookup[2][(one>>16) & 0xFF] ^
Crc32Lookup[3][(one>>24) & 0xFF];
#else
printf("LITTLE ENDIAN\n");
uint32_t one = *current++ ^ crc;
crc = Crc32Lookup[0][(one>>24) & 0xFF] ^
Crc32Lookup[1][(one>>16) & 0xFF] ^
Crc32Lookup[2][(one>> 8) & 0xFF] ^
Crc32Lookup[3][ one & 0xFF];
#endif
length -= 4;
}
const uint8_t* currentChar = (const uint8_t*) current;
// remaining 1 to 3 bytes (standard algorithm)
while (length-- > 0)
crc = (crc >> 8) ^ Crc32Lookup[0][(crc & 0xFF) ^ *currentChar++];
return ~crc; // same as crc ^ 0xFFFFFFFF
}
int main(int argc, char* argv[])
{
const char* test_string = "Hello World";
printf("strlen of test_string %ld\n",strlen(test_string));
uint32_t test_crc32_fb = Crc32FourBytes((void*)test_string,strlen(test_string),0);
printf("test_crc32_fb = %d\n",(int32_t) test_crc32_fb);
return 0;
}
结果
BIG ENDIAN
one is -1819043145
BIG ENDIAN
one is 861613025
test_crc32_fb = 202227096
我的Java实现如下
import java.nio.ByteOrder;
public class CRC32{
/// zlib's CRC32 polynomial
private static final long CrcPolynomial = 0xEDB88320L;
/// swap endianess
private static long swap(long x)
{
return ((x >> 24) & 0x000000FFL) |
((x >> 8) & 0x0000FF00L) |
((x << 8) & 0x00FF0000L) |
((x << 24) & 0xFF000000L);
}
final static long Crc32Lookup[][] = new long [][]
{
{ 0x00000000,0x77073096,0xEE0E612C,0x990951BA,0x076DC419,0x706AF48F,0xE963A535,0x9E6495A3,
0x0EDB8832,0x79DCB8A4,0xE0D5E91E,0x97D2D988,0x09B64C2B,0x7EB17CBD,0xE7B82D07,0x90BF1D91,
0x1DB71064,0x6AB020F2,0xF3B97148,0x84BE41DE,0x1ADAD47D,0x6DDDE4EB,0xF4D4B551,0x83D385C7,
0x136C9856,0x646BA8C0,0xFD62F97A,0x8A65C9EC,0x14015C4F,0x63066CD9,0xFA0F3D63,0x8D080DF5,
0x3B6E20C8,0x4C69105E,0xD56041E4,0xA2677172,0x3C03E4D1,0x4B04D447,0xD20D85FD,0xA50AB56B,
0x35B5A8FA,0x42B2986C,0xDBBBC9D6,0xACBCF940,0x32D86CE3,0x45DF5C75,0xDCD60DCF,0xABD13D59,
0x26D930AC,0x51DE003A,0xC8D75180,0xBFD06116,0x21B4F4B5,0x56B3C423,0xCFBA9599,0xB8BDA50F,
0x2802B89E,0x5F058808,0xC60CD9B2,0xB10BE924,0x2F6F7C87,0x58684C11,0xC1611DAB,0xB6662D3D,
0x76DC4190,0x01DB7106,0x98D220BC,0xEFD5102A,0x71B18589,0x06B6B51F,0x9FBFE4A5,0xE8B8D433,
0x7807C9A2,0x0F00F934,0x9609A88E,0xE10E9818,0x7F6A0DBB,0x086D3D2D,0x91646C97,0xE6635C01,
0x6B6B51F4,0x1C6C6162,0x856530D8,0xF262004E,0x6C0695ED,0x1B01A57B,0x8208F4C1,0xF50FC457,
0x65B0D9C6,0x12B7E950,0x8BBEB8EA,0xFCB9887C,0x62DD1DDF,0x15DA2D49,0x8CD37CF3,0xFBD44C65,
0x4DB26158,0x3AB551CE,0xA3BC0074,0xD4BB30E2,0x4ADFA541,0x3DD895D7,0xA4D1C46D,0xD3D6F4FB,
0x4369E96A,0x346ED9FC,0xAD678846,0xDA60B8D0,0x44042D73,0x33031DE5,0xAA0A4C5F,0xDD0D7CC9,
0x5005713C,0x270241AA,0xBE0B1010,0xC90C2086,0x5768B525,0x206F85B3,0xB966D409,0xCE61E49F,
0x5EDEF90E,0x29D9C998,0xB0D09822,0xC7D7A8B4,0x59B33D17,0x2EB40D81,0xB7BD5C3B,0xC0BA6CAD,
0xEDB88320,0x9ABFB3B6,0x03B6E20C,0x74B1D29A,0xEAD54739,0x9DD277AF,0x04DB2615,0x73DC1683,
0xE3630B12,0x94643B84,0x0D6D6A3E,0x7A6A5AA8,0xE40ECF0B,0x9309FF9D,0x0A00AE27,0x7D079EB1,
0xF00F9344,0x8708A3D2,0x1E01F268,0x6906C2FE,0xF762575D,0x806567CB,0x196C3671,0x6E6B06E7,
0xFED41B76,0x89D32BE0,0x10DA7A5A,0x67DD4ACC,0xF9B9DF6F,0x8EBEEFF9,0x17B7BE43,0x60B08ED5,
0xD6D6A3E8,0xA1D1937E,0x38D8C2C4,0x4FDFF252,0xD1BB67F1,0xA6BC5767,0x3FB506DD,0x48B2364B,
0xD80D2BDA,0xAF0A1B4C,0x36034AF6,0x41047A60,0xDF60EFC3,0xA867DF55,0x316E8EEF,0x4669BE79,
0xCB61B38C,0xBC66831A,0x256FD2A0,0x5268E236,0xCC0C7795,0xBB0B4703,0x220216B9,0x5505262F,
0xC5BA3BBE,0xB2BD0B28,0x2BB45A92,0x5CB36A04,0xC2D7FFA7,0xB5D0CF31,0x2CD99E8B,0x5BDEAE1D,
0x9B64C2B0,0xEC63F226,0x756AA39C,0x026D930A,0x9C0906A9,0xEB0E363F,0x72076785,0x05005713,
0x95BF4A82,0xE2B87A14,0x7BB12BAE,0x0CB61B38,0x92D28E9B,0xE5D5BE0D,0x7CDCEFB7,0x0BDBDF21,
0x86D3D2D4,0xF1D4E242,0x68DDB3F8,0x1FDA836E,0x81BE16CD,0xF6B9265B,0x6FB077E1,0x18B74777,
0x88085AE6,0xFF0F6A70,0x66063BCA,0x11010B5C,0x8F659EFF,0xF862AE69,0x616BFFD3,0x166CCF45,
0xA00AE278,0xD70DD2EE,0x4E048354,0x3903B3C2,0xA7672661,0xD06016F7,0x4969474D,0x3E6E77DB,
0xAED16A4A,0xD9D65ADC,0x40DF0B66,0x37D83BF0,0xA9BCAE53,0xDEBB9EC5,0x47B2CF7F,0x30B5FFE9,
0xBDBDF21C,0xCABAC28A,0x53B39330,0x24B4A3A6,0xBAD03605,0xCDD70693,0x54DE5729,0x23D967BF,
0xB3667A2E,0xC4614AB8,0x5D681B02,0x2A6F2B94,0xB40BBE37,0xC30C8EA1,0x5A05DF1B,0x2D02EF8D
},
....
};
public static int LongToInt(long value){
return (int)(value & 0xFFFFFFFFL);
}
public static long Complement(long value){
return (value ^ 0xFFFFFFFFL);
}
private static long Crc32FourBytes(byte[] data, long length, long previousCrc32, boolean is_bigendian)
{ //long crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF
//force long to unsigned integer below
long crc = Complement(previousCrc32);
int i = 0;
for( int j = data.length; j >= 4 ; j = j-4){
if (is_bigendian == true){
long one = data[i] ^ LongToInt(swap(crc));
System.out.format("one is %d\n", LongToInt(one));
crc = Crc32Lookup[0][LongToInt((one) & 0xFF)] ^
Crc32Lookup[1][LongToInt((one>>>8) & 0xFF)] ^
Crc32Lookup[2][LongToInt((one>>>16) & 0xFF)] ^
Crc32Lookup[3][LongToInt((one>>>24) & 0xFF)];
} else {
long one = data[i] ^ (crc);
crc = Crc32Lookup[0][LongToInt((one>>>24) & 0xFF)] ^
Crc32Lookup[1][LongToInt((one>>>16) & 0xFF)] ^
Crc32Lookup[2][LongToInt((one>>>8 ) & 0xFF)] ^
Crc32Lookup[3][LongToInt((one ) & 0xFF)];
}
i += 1;
//System.out.format("%d\n",k);
}
for (int k=0; k < data.length; k++)
{
crc = (LongToInt(crc) >>> 8) ^ Crc32Lookup[0][LongToInt((LongToInt(crc) & 0xFF) ^ data[k])];
}
return Complement(crc); //return crc ^ 0xFFFFFFFF;
}
public static void main(String []args){
System.out.println("Hello World");
final String str = "Hello World";
byte[] test_string = str.getBytes();
long test_crc32_fb = Crc32FourBytes(test_string,test_string.length,0,true);
System.out.format("%d\n",LongToInt(test_crc32_fb));
}
}
结果
one is -73
one is 1105837251
369408888
我不确定我在代码中出错的地方。感谢。
答案 0 :(得分：2)
C代码将current声明为uint32_t*，指向uint32_t的指针：
const uint32_t* current = (const uint32_t*) data;
因此（在循环内）
uint32_t one = *current++ ^ swap(crc);
一次读取并处理4个字节。
另一方面，您的Java代码仅适用于输入中的单个字节：
long one = data[i] ^ LongToInt(swap(crc));
答案 1 :(得分：1)
您需要使用asIntBuffer()来访问输入字节数组data，而不是一系列四字节字。这相当于C cast const uint32_t* current = (const uint32_t*) data;，它current一次只能访问data四个字节。
答案 2 :(得分：0)
感谢您的指导，特别是@ThomasKläger和@Mark Adler，我得到了这个工作。
//helper functions
public static final byte[] getByteArrayFromIndex(byte[] data, int index){
return new byte[] {
data[index],
data[index+1],
data[index+2],
data[index+3]
};
}
public static final byte getByteFromIndex(byte[] data, int index){
return data[index];
}
public static long getLongFromByteArray(byte[] array){
return ByteBuffer.wrap(array)
.order(ByteOrder.LITTLE_ENDIAN).getInt() & 0xFFFFFFFFL;
}
private static byte[] convertLongToByteArray(long l) {
byte[] b = new byte[4];
if(java.nio.ByteOrder.nativeOrder() == ByteOrder.LITTLE_ENDIAN){
for (int i=0; i<4; i++) {
b[i] = (byte)(l % 256) ;
l = l / 256;
}
}else{
for (int i=3; i>=0; i--) {
b[i] = (byte)(l % 256) ;
l = l / 256;
}
}
return b;
}
//Crc32FourBytes
private static long Crc32FourBytes(byte[] data, long length, long previousCrc32, boolean is_bigendian)
{ //long crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF
//force long to unsigned integer below
long crc = Complement(previousCrc32);
int i = 0;
int j = data.length;
long temp = 0;
for( ; j >= 4 ; j = j-4){
if (is_bigendian == true){
temp = getLongFromByteArray(getByteArrayFromIndex(data,i));
long one = temp ^ swap(crc);
System.out.format("one is %d\n", LongToInt(one));
crc = Crc32Lookup[0][LongToInt((one) & 0xFF)] ^
Crc32Lookup[1][LongToInt((one>>>8) & 0xFF)] ^
Crc32Lookup[2][LongToInt((one>>>16) & 0xFF)] ^
Crc32Lookup[3][LongToInt((one>>>24) & 0xFF)];
System.out.format("crc is %d\n", LongToInt(crc));
} else {
temp = getLongFromByteArray(getByteArrayFromIndex(data,i));
long one = temp ^ (crc);
crc = Crc32Lookup[0][LongToInt((one>>>24) & 0xFF)] ^
Crc32Lookup[1][LongToInt((one>>>16) & 0xFF)] ^
Crc32Lookup[2][LongToInt((one>>>8 ) & 0xFF)] ^
Crc32Lookup[3][LongToInt((one ) & 0xFF)];
System.out.format("crc is %d\n", LongToInt(crc));
}
i += 4;
//System.out.format("%d\n",k);
}
// Remaining 1 to 3 bytes (standard algorithm)
for (int k=data.length-i; k >0; k--)
{
crc = (LongToInt(crc) >>> 8) ^ Crc32Lookup[0][LongToInt((LongToInt(crc) & 0xFF) ^ LongToInt(data[data.length-k]))];
System.out.format("=> crc is %d\n", LongToInt(crc));
}
return Complement(crc); //return crc ^ 0xFFFFFFFF;
}
通过扩展我还得到了8分工作。
private static long Crc32EightBytes(byte[] data, long length, long previousCrc32, boolean is_bigendian)
{ //long crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF
//force long to unsigned integer below
long crc = Complement(previousCrc32);
int i = 0;
int j = data.length;
long temp = 0;
for( ; j >= 8 ; j = j-8){
if (is_bigendian == true){
//First set of four
temp = getLongFromByteArray(getByteArrayFromIndex(data,i));
long one = temp ^ swap(crc);
//Second set of four
i += 4;
temp = getLongFromByteArray(getByteArrayFromIndex(data,i));
long two = temp;
System.out.format("one is %d\n", LongToInt(one));
System.out.format("two is %d\n", LongToInt(one));
crc = Crc32Lookup[0][LongToInt((two ) & 0xFF)] ^
Crc32Lookup[1][LongToInt((two>>>8) & 0xFF)] ^
Crc32Lookup[2][LongToInt((two>>>16) & 0xFF)] ^
Crc32Lookup[3][LongToInt((two>>>24) & 0xFF)] ^
Crc32Lookup[4][LongToInt((one ) & 0xFF)] ^
Crc32Lookup[5][LongToInt((one>>>8) & 0xFF)] ^
Crc32Lookup[6][LongToInt((one>>>16) & 0xFF)] ^
Crc32Lookup[7][LongToInt((one>>>24) & 0xFF)];
System.out.format("crc is %d\n", LongToInt(crc));
} else {
//First set of four
temp = getLongFromByteArray(getByteArrayFromIndex(data,i));
long one = temp ^ (crc);
//Second set of four
i += 4;
temp = getLongFromByteArray(getByteArrayFromIndex(data,i));
long two = temp;
crc = Crc32Lookup[0][LongToInt((two>>>24) & 0xFF)] ^
Crc32Lookup[1][LongToInt((two>>>16) & 0xFF)] ^
Crc32Lookup[2][LongToInt((two>>>8 ) & 0xFF)] ^
Crc32Lookup[3][LongToInt((two ) & 0xFF)] ^
Crc32Lookup[4][LongToInt((one>>>24) & 0xFF)] ^
Crc32Lookup[5][LongToInt((one>>>16) & 0xFF)] ^
Crc32Lookup[6][LongToInt((one>>>8 ) & 0xFF)] ^
Crc32Lookup[7][LongToInt((one ) & 0xFF)];
System.out.format("crc is %d\n", LongToInt(crc));
}
//Increment by 4 here because we increment by another 4 for second set in the iterative loop making total increment by 4+4 = 8
i += 4;
System.out.format("%d\n",i);
}
// Remaining 1 to 7 bytes (standard algorithm)
for (int k=data.length-i; k >0; k--)
{
crc = (LongToInt(crc) >>> 8) ^ Crc32Lookup[0][LongToInt((LongToInt(crc) & 0xFF) ^ LongToInt(data[data.length-k]))];
System.out.format("=>>>> crc is %d\n", LongToInt(crc));
}
return Complement(crc); //return crc ^ 0xFFFFFFFF;
}
答案 3 :(得分：-1)
您需要使用无符号右移：>>>而不是>>。 C代码使用无符号整数，具有相同的效果。