Diffrent result for CRC32 in c++ and java

Question

I am trying to calculate CRC32 checksum in C++. But i'm still getting bad results.

C++ code:

class CRC32
{

public:

    CRC32() {
        unsigned int poly = 0xedb88320;
        unsigned int temp = 0;
        for(unsigned int i = 0; i < 256; ++i) {
            temp = i;
            for(int j = 8; j > 0; --j) {
                if((temp & 1) == 1) {
                    temp = (unsigned int)((temp >> 1) ^ poly);
                }else {
                    temp >>= 1;
                }
            }
            table[i] = temp;
        }
    }

    unsigned int ComputeChecksum(byte* bytes,size_t size) {
        unsigned int crc = 0xffffffff;
        for(int i = 0; i < size; ++i) {
            byte index = (byte)(((crc) & 0xff) ^ bytes[i]);
            crc = (unsigned int)((crc >> 8) ^ table[index]);
        }
        return ~crc;
    }

private:
    unsigned int table[256];
};

This java code works fine:

private int stmCrc32(byte abyte0[])
    {
        CRC32 crc32 = new CRC32();
        crc32.update(abyte0);
        return (int)(-1L ^ crc32.getValue());
    }

This is hex string of example data (result should be 1909660290):

00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:01:00:12:00:59:57:52:74:61:57:34:36:59:57:52:74:61:57:34:3d:0d:0a:00:00

Cannot reproduce.. The above code is correct for C++ and it works.. If you went to: http://www.tools4noobs.com/online_php_functions/crc32/ and entered: `0000000000000000000000000000000000000000010012005957527461573436595752746157343d0d0a0000` It'd print: `5be919e6` which is the same as: http://ideone.com/dIKU38 — Brandon, Jul 27 '14 at 16:03
@Brandon Ok c++ code is correct. But it gives diffrent result then java code (c - 1542003174, java 1909660290), and in may case java code result is correct, so how to make it works? — Wojciech Król, Jul 27 '14 at 16:17
@user3599093 So be it. That’s not a problem. You are changing the result, of course it’s different from the C++ result – what do you expect?! — Konrad Rudolph, Jul 27 '14 at 16:17
@KonradRudolph Java code is not mine. I just need to make my c++ code return the same value that java code does. — Wojciech Król, Jul 27 '14 at 16:23

score 1 · Accepted Answer · answered Jul 27 '14 at 17:12

The two implementations appear to be identical. You just missed out in the surrounding code. In C++, do exactly what they did in Java (however dumb that may be), and the result will be the same.

byte data[] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x12, 0x00, 0x59, 0x57, 0x52, 0x74, 0x61, 0x57, 0x34, 0x36, 0x59, 0x57, 0x52, 0x74, 0x61, 0x57, 0x34, 0x3d, 0x0d, 0x0a, 0x00, 0x00};
CRC32 crc;
int result = (int)(-1L ^ crc.ComputeChecksum(data, sizeof(data)));
std::cout << result << std::endl;

Result: 1909660290

Diffrent result for CRC32 in c++ and java

1 Answers1