2

我有一些需要测试的 CRC 方法。这些方法不是我自己写的。我认为最好的方法是使用不同的技术实现 CRC 算法，然后比较结果。

目前所有的 CRC 例程都以表格驱动的格式编写。我似乎找不到任何教程来解释如何将代码转换为按位实现。我确定这是我对 CRC 的工作原理缺乏了解。

如果有人可以提供一个相同的 CRC 例程的示例，实现了 2 种不同的方式，那就太好了。我在互联网上进行了搜索，并没有发现很多对我的问题有帮助的东西。

这是我需要测试的一种 CRC 算法的示例代码：

// This table implements the EPO CRC16 algorithm with a polynomial of 0x17531
static const uint16 s_EPOCRC16Table[] =
{
   0x0000U, 0x7531U, 0xEA62U, 0x9F53U, 0xA1F5U, 0xD4C4U, 0x4B97U, 0x3EA6U,
   0x36DBU, 0x43EAU, 0xDCB9U, 0xA988U, 0x972EU, 0xE21FU, 0x7D4CU, 0x087DU,
   0x6DB6U, 0x1887U, 0x87D4U, 0xF2E5U, 0xCC43U, 0xB972U, 0x2621U, 0x5310U,
   0x5B6DU, 0x2E5CU, 0xB10FU, 0xC43EU, 0xFA98U, 0x8FA9U, 0x10FAU, 0x65CBU,
   0xDB6CU, 0xAE5DU, 0x310EU, 0x443FU, 0x7A99U, 0x0FA8U, 0x90FBU, 0xE5CAU,
   0xEDB7U, 0x9886U, 0x07D5U, 0x72E4U, 0x4C42U, 0x3973U, 0xA620U, 0xD311U,
   0xB6DAU, 0xC3EBU, 0x5CB8U, 0x2989U, 0x172FU, 0x621EU, 0xFD4DU, 0x887CU,
   0x8001U, 0xF530U, 0x6A63U, 0x1F52U, 0x21F4U, 0x54C5U, 0xCB96U, 0xBEA7U,
   0xC3E9U, 0xB6D8U, 0x298BU, 0x5CBAU, 0x621CU, 0x172DU, 0x887EU, 0xFD4FU,
   0xF532U, 0x8003U, 0x1F50U, 0x6A61U, 0x54C7U, 0x21F6U, 0xBEA5U, 0xCB94U,
   0xAE5FU, 0xDB6EU, 0x443DU, 0x310CU, 0x0FAAU, 0x7A9BU, 0xE5C8U, 0x90F9U,
   0x9884U, 0xEDB5U, 0x72E6U, 0x07D7U, 0x3971U, 0x4C40U, 0xD313U, 0xA622U,
   0x1885U, 0x6DB4U, 0xF2E7U, 0x87D6U, 0xB970U, 0xCC41U, 0x5312U, 0x2623U,
   0x2E5EU, 0x5B6FU, 0xC43CU, 0xB10DU, 0x8FABU, 0xFA9AU, 0x65C9U, 0x10F8U,
   0x7533U, 0x0002U, 0x9F51U, 0xEA60U, 0xD4C6U, 0xA1F7U, 0x3EA4U, 0x4B95U,
   0x43E8U, 0x36D9U, 0xA98AU, 0xDCBBU, 0xE21DU, 0x972CU, 0x087FU, 0x7D4EU,
   0xF2E3U, 0x87D2U, 0x1881U, 0x6DB0U, 0x5316U, 0x2627U, 0xB974U, 0xCC45U,
   0xC438U, 0xB109U, 0x2E5AU, 0x5B6BU, 0x65CDU, 0x10FCU, 0x8FAFU, 0xFA9EU,
   0x9F55U, 0xEA64U, 0x7537U, 0x0006U, 0x3EA0U, 0x4B91U, 0xD4C2U, 0xA1F3U,
   0xA98EU, 0xDCBFU, 0x43ECU, 0x36DDU, 0x087BU, 0x7D4AU, 0xE219U, 0x9728U,
   0x298FU, 0x5CBEU, 0xC3EDU, 0xB6DCU, 0x887AU, 0xFD4BU, 0x6218U, 0x1729U,
   0x1F54U, 0x6A65U, 0xF536U, 0x8007U, 0xBEA1U, 0xCB90U, 0x54C3U, 0x21F2U,
   0x4439U, 0x3108U, 0xAE5BU, 0xDB6AU, 0xE5CCU, 0x90FDU, 0x0FAEU, 0x7A9FU,
   0x72E2U, 0x07D3U, 0x9880U, 0xEDB1U, 0xD317U, 0xA626U, 0x3975U, 0x4C44U,
   0x310AU, 0x443BU, 0xDB68U, 0xAE59U, 0x90FFU, 0xE5CEU, 0x7A9DU, 0x0FACU,
   0x07D1U, 0x72E0U, 0xEDB3U, 0x9882U, 0xA624U, 0xD315U, 0x4C46U, 0x3977U,
   0x5CBCU, 0x298DU, 0xB6DEU, 0xC3EFU, 0xFD49U, 0x8878U, 0x172BU, 0x621AU,
   0x6A67U, 0x1F56U, 0x8005U, 0xF534U, 0xCB92U, 0xBEA3U, 0x21F0U, 0x54C1U,
   0xEA66U, 0x9F57U, 0x0004U, 0x7535U, 0x4B93U, 0x3EA2U, 0xA1F1U, 0xD4C0U,
   0xDCBDU, 0xA98CU, 0x36DFU, 0x43EEU, 0x7D48U, 0x0879U, 0x972AU, 0xE21BU,
   0x87D0U, 0xF2E1U, 0x6DB2U, 0x1883U, 0x2625U, 0x5314U, 0xCC47U, 0xB976U,
   0xB10BU, 0xC43AU, 0x5B69U, 0x2E58U, 0x10FEU, 0x65CFU, 0xFA9CU, 0x8FADU,
};

/**
 * This routine returns the CRC-16 of Cp_ptr.
 * This CRC routine is reversed to match the routine used in the EPO.
 *
 * @param  const uint8 *Cp_ptr - data pointer to the bit string to be calculated over
 * @param  const uint32 Len    - the number of bytes pointed to by Cp_ptr
 * @return the calculated 16-bit CRC
 * @ureq
 *    -# epoCRC16() shall calculate a 16-bit CRC on a block of data starting at an address of a specified length.
 *    -# epoCRC16() shall ASSERT if the passed in pointer is NULL.
 */
uint16 epoCRC16( const uint8 *Cp_ptr, const uint32 Len )
{
   ASSERT( Cp_ptr != NULL );

   // local variable
   uint16 crc = 0x0;

   // calculate the crc
   for ( uint16 i = Len; i > 0; i-- )
   {
      const uint8 TableIndex = ( *Cp_ptr ^ static_cast<uint8>( crc >> 8 ) );
      crc = static_cast<uint16>( crc << 8 );
      crc = ( crc ^ s_EPOCRC16Table[TableIndex] );
      Cp_ptr++;
   }

   return crc;
}
4

3 回答 3

6

您首先需要 CRC 多项式，您可以在此类表的第二个条目或第 128 个条目中找到它，具体取决于 CRC 的位顺序。或者在这种情况下，您可以在评论中找到它0x17531。1后面是多项式的x第一项，它简单地定义了 CRC 的长度。它在计算中被删除。您可以0x7531在表格的第二个条目中找到。

此例程（在 C 中）仅使用多项式生成上表：

void make_crc_table(unsigned poly, unsigned *table)
{
    unsigned n, k, crc;

    for (n = 0; n < 256; n++) {
        crc = n << 8;
        for (k = 0; k < 8; k++)
            crc = crc & 0x8000 ? (crc << 1) ^ poly : crc << 1;
        table[n] = crc & 0xffff;
    }
}

它会被这样称呼：make_crc_table(0x7531, table)wheretable是一个由 256 个无符号整数组成的数组。

逐位 CRC 例程看起来大致相同：

unsigned epobit(unsigned char *buf, unsigned len, unsigned poly)
{
    unsigned n, k, crc = 0;

    for (n = len; n > 0; n--) {
        crc ^= (*buf++ << 8);
        for (k = 0; k < 8; k++)
            crc = crc & 0x8000 ? (crc << 1) ^ poly : crc << 1;
    }
    return crc & 0xffff;
}
于 2012-08-07T02:31:53.293 回答
2

对于工具，请查看pycrc，它具有用于任意 CRC 的代码生成器。

有关 CRC 计算的说明，请参阅A Painless Guide to CRC Error Detection Algorithms。

于 2012-08-07T02:36:17.673 回答
0 
// Bitise and tablewise CRC-16 can be compared by following source code with polynomial 0x17531 !

// CRC.cpp : 
//

#include "stdafx.h"
#include "CRC.h"

#include "afx.h"
#include <conio.h>

#ifdef _DEBUG
#define new DEBUG_NEW
#endif


CWinApp theApp;

using namespace std;

#define BUFLENGTH (0x100000*1)  //0x100000=1MB

void makeCRC16Table();
void crc16update(unsigned short &crc0, const void *data, int length);
void crc16updateBitwise(unsigned short &crc0, const void *data, int length);

static byte crc8Table[256];
static unsigned short crc16Table[256];
static unsigned long crc32Table[256];

int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{
    int nRetCode = 0;

    unsigned char crc8=0x00;
    unsigned short crc16=0x0000;
    unsigned long crc32=0x00000000;

    byte *dataBuf = new byte[BUFLENGTH];
    if(dataBuf==0)
    {
        cout<<"Not enough memory allocation to dataBuf[] !";
        while(!_kbhit());
        return nRetCode;
    }
    for(int i=0; i<BUFLENGTH; i++)
        dataBuf[i]=i+1;

    makeCRC16Table();
    crc16=0x00;
    crc16update(crc16, dataBuf, BUFLENGTH);
    crc16=0x00;
    crc16updateBitwise(crc16, dataBuf, BUFLENGTH);

    delete[] dataBuf;

    while(!_kbhit());

    }

    return nRetCode;
}

void makeCRC16Table()
{
    /* generate a table for a byte-wise 16-bit CRC caculation on the polynomial ;
      */
    CString soutputfile=_T("crc16Table.txt");
    CString soutputbuffer;
    CStdioFile fileTarget( soutputfile, CFile::modeCreate | CFile::modeWrite );
    int i,j;
    unsigned long poly, cc;
    /* terms of polynomial defining this crc (except x^16) */
    //static const byte pp[]={0,5,12};
    static const byte pp[]={0,2,15};

    /* make exclusive-or pattern from polynomial 0x1021 */
    poly=0;
    //for(i=0; i<sizeof(pp)/sizeof(byte); i++) 
    //  poly|=1<<pp[i];
    poly=0x7531;
    //poly=0x1021;
    //poly=0x8005;

    for(i=0; i<256; i++) {
        cc=i<<8; 
        for(j=0; j<8; j++) {
            cc=(cc&0x8000)?(poly^(cc<<1)):(cc<<1);  //MSB first transmission

        }
        crc16Table[i]=cc&0xffff;

        soutputbuffer.Format("%3d:%04X\n", i, crc16Table[i]);
        fileTarget.WriteString(soutputbuffer);
    }
    fileTarget.Close();
    //ShellExecute(NULL, NULL, soutputfile, NULL, NULL, SW_SHOWNORMAL);
}

void crc16update(unsigned short &crc0, const void *data, int length)
{
    CString soutputfile=_T("crc16.txt");
    cout<<"\n"<<soutputfile<<"\n";

    CString soutputbuffer, soutputbufferTotal;
    CStdioFile fileTarget( soutputfile, CFile::modeCreate | CFile::modeWrite );

    int percentage=0, ntemp;
    unsigned short crc,crc1;
    const unsigned char *buf=(const unsigned char *)data;
    int i=0, j;
    crc=crc0;
    while(i<length) 
    {
        ntemp=i/(length/100);
        if(ntemp!=percentage)
        {
            soutputbuffer.Format("%d%% ", percentage );
            cout<<soutputbuffer;
            percentage=ntemp;
            if(ntemp<0)
                int nn=0;
        }

        crc1=crc;
        j = ((crc >> 8) ^ buf[i]) & 0xff;
        crc = (crc << 8) ^ crc16Table[j];

        soutputbuffer.Format("%d:%02X:%04X>%04X\n", i, buf[i], crc1, crc );
        fileTarget.WriteString(soutputbuffer);
        i++;
    }
    soutputbuffer.Format("\n%04X>%04X", crc1, crc );
    cout<<soutputbuffer;
    crc0=crc;
    fileTarget.Close();
    //ShellExecute(NULL, NULL, soutputfile, NULL, NULL, SW_SHOWNORMAL);
}

void crc16updateBitwise(unsigned short &crc0, const void *data, int length)
{
    CString soutputfile=_T("crc16BW.txt");
    cout<<"\n"<<soutputfile<<"\n";

    CString soutputbuffer;
    CStdioFile fileTarget( soutputfile, CFile::modeCreate | CFile::modeWrite );

    static const byte BitTable[]={0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80};
    int percentage=0, ntemp;
    unsigned long poly;
    /* terms of polynomial defining this crc (except x^16) */
    //static const byte pp[]={0,5,12};//CCITT
    static const byte pp[]={0,2,15};//GENERAL

    /* make exclusive-or pattern from polynomial 0x1021 */
    int i;
    poly=0;
    //for(i=0; i<sizeof(pp)/sizeof(byte); i++) 
    //  poly|=1<<pp[i];
    //poly=0x8005;
    poly=0x7531;

    unsigned short crc,crc1;
    const unsigned char *buf=(const unsigned char *)data;
    byte a,b,c;
    crc=crc0;
    i=0;
    while(i<length) 
    {
        ntemp=i/(length/100);
        if(ntemp!=percentage)
        {
            soutputbuffer.Format("%d%% ", percentage );
            cout<<soutputbuffer;
            percentage=ntemp;
        }
        crc1=crc;
        for(int j=0; j<8; j++) {
            a=(crc&0x8000)?1:0;//x^16
            b=(buf[i]&BitTable[7-j])?1:0;////MSB first transmission 
            c=a^b;
            crc=(c?(poly^(crc<<1)):(crc<<1))&0xffff;
        }
        soutputbuffer.Format("%d:%02X:%04X>%04X\n", i, buf[i], crc1&0xffff, crc&0xffff );
        fileTarget.WriteString(soutputbuffer);
        i++;
    }
    soutputbuffer.Format("\n%04X>%04X", crc1&0xffff, crc&0xffff );
    cout<<soutputbuffer;
    crc0=crc;
    fileTarget.Close();
    //ShellExecute(NULL, NULL, soutputfile, NULL, NULL, SW_SHOWNORMAL);
}
于 2012-12-21T14:59:59.983 回答