C / C++ / MFC

john5632 wrote:

Is there a way to make it faster?

john5632 wrote:

Can I get the string legnth from CRC?

john5632 wrote:

But I read somwhat like this somewhere

john5632 wrote:

...my aim is to get the string which generate the same CRC value

john5632 wrote:

my aim is to get the string which generate the same CRC value

john5632 wrote:

I know I can not construct data from CRC, my aim is
to get the string which generate the same CRC value

#include <iostream.h>



// The CRC lookup table  size is  8x32=256
const static unsigned int table[] =
{
    0x000000000, 0x077073096, 0x0EE0E612C, 0x0990951BA, 0x0076DC419, 0x0706AF48F, 0x0E963A535, 0x09E6495A3,
    0x00EDB8832, 0x079DCB8A4, 0x0E0D5E91E, 0x097D2D988, 0x009B64C2B, 0x07EB17CBD, 0x0E7B82D07, 0x090BF1D91,
    0x01DB71064, 0x06AB020F2, 0x0F3B97148, 0x084BE41DE, 0x01ADAD47D, 0x06DDDE4EB, 0x0F4D4B551, 0x083D385C7,
    0x0136C9856, 0x0646BA8C0, 0x0FD62F97A, 0x08A65C9EC, 0x014015C4F, 0x063066CD9, 0x0FA0F3D63, 0x08D080DF5,
    0x03B6E20C8, 0x04C69105E, 0x0D56041E4, 0x0A2677172, 0x03C03E4D1, 0x04B04D447, 0x0D20D85FD, 0x0A50AB56B,
    0x035B5A8FA, 0x042B2986C, 0x0DBBBC9D6, 0x0ACBCF940, 0x032D86CE3, 0x045DF5C75, 0x0DCD60DCF, 0x0ABD13D59,
    0x026D930AC, 0x051DE003A, 0x0C8D75180, 0x0BFD06116, 0x021B4F4B5, 0x056B3C423, 0x0CFBA9599, 0x0B8BDA50F,
    0x02802B89E, 0x05F058808, 0x0C60CD9B2, 0x0B10BE924, 0x02F6F7C87, 0x058684C11, 0x0C1611DAB, 0x0B6662D3D,
    0x076DC4190, 0x001DB7106, 0x098D220BC, 0x0EFD5102A, 0x071B18589, 0x006B6B51F, 0x09FBFE4A5, 0x0E8B8D433,
    0x07807C9A2, 0x00F00F934, 0x09609A88E, 0x0E10E9818, 0x07F6A0DBB, 0x0086D3D2D, 0x091646C97, 0x0E6635C01,
    0x06B6B51F4, 0x01C6C6162, 0x0856530D8, 0x0F262004E, 0x06C0695ED, 0x01B01A57B, 0x08208F4C1, 0x0F50FC457,
    0x065B0D9C6, 0x012B7E950, 0x08BBEB8EA, 0x0FCB9887C, 0x062DD1DDF, 0x015DA2D49, 0x08CD37CF3, 0x0FBD44C65,
    0x04DB26158, 0x03AB551CE, 0x0A3BC0074, 0x0D4BB30E2, 0x04ADFA541, 0x03DD895D7, 0x0A4D1C46D, 0x0D3D6F4FB,
    0x04369E96A, 0x0346ED9FC, 0x0AD678846, 0x0DA60B8D0, 0x044042D73, 0x033031DE5, 0x0AA0A4C5F, 0x0DD0D7CC9,
    0x05005713C, 0x0270241AA, 0x0BE0B1010, 0x0C90C2086, 0x05768B525, 0x0206F85B3, 0x0B966D409, 0x0CE61E49F,
    0x05EDEF90E, 0x029D9C998, 0x0B0D09822, 0x0C7D7A8B4, 0x059B33D17, 0x02EB40D81, 0x0B7BD5C3B, 0x0C0BA6CAD,
    0x0EDB88320, 0x09ABFB3B6, 0x003B6E20C, 0x074B1D29A, 0x0EAD54739, 0x09DD277AF, 0x004DB2615, 0x073DC1683,
    0x0E3630B12, 0x094643B84, 0x00D6D6A3E, 0x07A6A5AA8, 0x0E40ECF0B, 0x09309FF9D, 0x00A00AE27, 0x07D079EB1,
    0x0F00F9344, 0x08708A3D2, 0x01E01F268, 0x06906C2FE, 0x0F762575D, 0x0806567CB, 0x0196C3671, 0x06E6B06E7,
    0x0FED41B76, 0x089D32BE0, 0x010DA7A5A, 0x067DD4ACC, 0x0F9B9DF6F, 0x08EBEEFF9, 0x017B7BE43, 0x060B08ED5,
    0x0D6D6A3E8, 0x0A1D1937E, 0x038D8C2C4, 0x04FDFF252, 0x0D1BB67F1, 0x0A6BC5767, 0x03FB506DD, 0x048B2364B,
    0x0D80D2BDA, 0x0AF0A1B4C, 0x036034AF6, 0x041047A60, 0x0DF60EFC3, 0x0A867DF55, 0x0316E8EEF, 0x04669BE79,
    0x0CB61B38C, 0x0BC66831A, 0x0256FD2A0, 0x05268E236, 0x0CC0C7795, 0x0BB0B4703, 0x0220216B9, 0x05505262F,
    0x0C5BA3BBE, 0x0B2BD0B28, 0x02BB45A92, 0x05CB36A04, 0x0C2D7FFA7, 0x0B5D0CF31, 0x02CD99E8B, 0x05BDEAE1D,
    0x09B64C2B0, 0x0EC63F226, 0x0756AA39C, 0x0026D930A, 0x09C0906A9, 0x0EB0E363F, 0x072076785, 0x005005713,
    0x095BF4A82, 0x0E2B87A14, 0x07BB12BAE, 0x00CB61B38, 0x092D28E9B, 0x0E5D5BE0D, 0x07CDCEFB7, 0x00BDBDF21,
    0x086D3D2D4, 0x0F1D4E242, 0x068DDB3F8, 0x01FDA836E, 0x081BE16CD, 0x0F6B9265B, 0x06FB077E1, 0x018B74777,
    0x088085AE6, 0x0FF0F6A70, 0x066063BCA, 0x011010B5C, 0x08F659EFF, 0x0F862AE69, 0x0616BFFD3, 0x0166CCF45,
    0x0A00AE278, 0x0D70DD2EE, 0x04E048354, 0x03903B3C2, 0x0A7672661, 0x0D06016F7, 0x04969474D, 0x03E6E77DB,
    0x0AED16A4A, 0x0D9D65ADC, 0x040DF0B66, 0x037D83BF0, 0x0A9BCAE53, 0x0DEBB9EC5, 0x047B2CF7F, 0x030B5FFE9,
    0x0BDBDF21C, 0x0CABAC28A, 0x053B39330, 0x024B4A3A6, 0x0BAD03605, 0x0CDD70693, 0x054DE5729, 0x023D967BF,
    0x0B3667A2E, 0x0C4614AB8, 0x05D681B02, 0x02A6F2B94, 0x0B40BBE37, 0x0C30C8EA1, 0x05A05DF1B, 0x02D02EF8D
};


const int crcSIZE = 5;
class Test
{

    public:
    // The CRC lookup table
    const static unsigned int table[crcSIZE];

    unsigned int GetCRC32(const unsigned char* bytes, const unsigned int len)
    {
        unsigned int crc = 0xFFFFFFFF;
        unsigned char byte=0;

        for(unsigned int i = 0; i < len; i++)
        {
            crc = (crc >> 8) ^ table[byte];
            cout<<crc<<"\t";
        }
        return crc ^ 0xFFFFFFFF;
        }
    };

    const unsigned int Test::table[crcSIZE] =
    {
    0x000000000, 0x077073096, 0x0EE0E612C, 0x0990951BA, 0x0076DC419

};

int main( )
{
    unsigned char bytes[] = { 0xAA, 0xBB, 0xCC };
    Test tst;
    tst.GetCRC32(bytes, 3);
    cout<<"\n";

return 0;
}

Chuck O'Toole wrote:

Unless you are trying to fool some other program who knows the CRC32 of the data it wants and you are trying to pump some junk at it for some amusing or nefarious reason.

Richard MacCutchan wrote:

Having read all the above answers why do you persist in believing this is
possible?