Question

我有一个遥测流，它通过一个硬件CRC生成器，将CRC附加到每个遥测帧的末尾。现在我正在尝试做一些事来验证硬件生成的CRC。我有旧的遗留代码（见下文），它计算正确的CRC（多次验证）。然而它很慢，因为每个遥测帧都是300多个字节，并且可以处理超过10,000,000个帧。

经过一些研究后，我发现一些文献指出了一种表驱动的方法。传统方法使用Poly of 0x8005，在处理之前反转每个字节的位顺序，并将CRC初始化为零。但是，在为具有反向和非反向输入的多边形构建表之后，只是尝试通过数据的第一个字节（0x10），我无法获得与遗留方法生成的内容相匹配的任何内容。

在calcCRC16函数（下面）中，现有方法检查LSB，其他人似乎检查MSB ......并且位移到右边，我看到的其他示例在左边。我迷失了为什么这是特别的，因为在将顺序交换到此函数之前交换了位顺序。我试过在线计算器＆amp;在表格中手动执行查找，将poly从8005切换到A001（反向），正常和反向输入字节，以及我能想到的每种组合，但无法获得任何表格方法来匹配我知道的遗留代码正确的我们的硬件实现。

如果我错过了一些明显的东西，有人可以帮助我吗？您将如何创建基于表的方法来创建相同的输出？我是C ++的新手，并不熟悉CRC生成，可能会忽略一些基本的东西。根据硬件CRC验证的示例代码和输出如下：

示例代码：我只是用知道的遥测流硬编码了几个字节作为示例

/** ********************************************************************************
* TEST CRC METHOD
*******************************************************************************/
#include <iostream>

using namespace std;

unsigned char swapBits(unsigned char d);
void calcCRC16(unsigned int *CRCVal, unsigned char value);

/** **************************************************************************
*   @function   main
*   TEST CRC METHOd
*******************************************************************************/
int main(int argc, char* argv[])
{
    short          dataLength = 5;
    unsigned int   givenCrc;
    unsigned int   calcCrc;    
    unsigned char byte[] = {0x10,0xbb,0x42,0x4d,0xfd};

    /* Init CRC. */
    calcCrc = 0;
    cout << "Inital CRC = " << hex << calcCrc << "\n";
    /* Read frame data. */
    for (int i = 0; i < dataLength; i++)
    {
        cout << "byte    = " << hex << static_cast<int16_t>(byte[i]) << " ";
        calcCRC16(&calcCrc, swapBits(byte[i]));
        cout << "calcCRC = " << hex << calcCrc << "\n";
     }
}

/** ********************************************************************
*   @function   swapBits
*   Swaps the bits so they match the order sent to CRC Gen Hardware
************************************************************************/
unsigned char swapBits(unsigned char d)
{
    unsigned char t = 0;
    int i           = 0;
    int n           = 0x80;

    for(i=0x01; i<0x100; i=i<<1)
    {
        if (d & i)
        {
            t|=n;
        }
        n=n>>1;
    }
    return t;
}

/** ********************************************************************
*   @function   calcCRC16
*   WORKING METHOD VERIFIED AGAINST CRC HARDWARE
************************************************************************/
void calcCRC16(unsigned int *CRCVal, unsigned char value)
{
    unsigned char lsb;
    unsigned char bcnt;

    for (bcnt=0 ; bcnt<8 ; bcnt++)
    {
        lsb = (value ^ *CRCVal) & 0x01;
        *CRCVal >>= 1;
        value >>= 1;
        if (lsb != 0)
        {
            *CRCVal ^= 0x8005;
        }
    }
}

输出：
    初始CRC = 0
    byte = 10 calcCRC = b804
    byte = bb calcCRC = 1fb8
    byte = 42 calcCRC = 461d
    byte = 4d calcCRC = 3d47
    byte = fd calcCRC = 683e

Answer 1

rev16(crc16(0, buf, len))将为您提供列出的CRC。

#include <stdio.h>

static unsigned short crc16_table[] = {
    0x0000, 0xa001, 0xe003, 0x4002, 0x6007, 0xc006, 0x8004, 0x2005,
    0xc00e, 0x600f, 0x200d, 0x800c, 0xa009, 0x0008, 0x400a, 0xe00b,
    0x201d, 0x801c, 0xc01e, 0x601f, 0x401a, 0xe01b, 0xa019, 0x0018,
    0xe013, 0x4012, 0x0010, 0xa011, 0x8014, 0x2015, 0x6017, 0xc016,
    0x403a, 0xe03b, 0xa039, 0x0038, 0x203d, 0x803c, 0xc03e, 0x603f,
    0x8034, 0x2035, 0x6037, 0xc036, 0xe033, 0x4032, 0x0030, 0xa031,
    0x6027, 0xc026, 0x8024, 0x2025, 0x0020, 0xa021, 0xe023, 0x4022,
    0xa029, 0x0028, 0x402a, 0xe02b, 0xc02e, 0x602f, 0x202d, 0x802c,
    0x8074, 0x2075, 0x6077, 0xc076, 0xe073, 0x4072, 0x0070, 0xa071,
    0x407a, 0xe07b, 0xa079, 0x0078, 0x207d, 0x807c, 0xc07e, 0x607f,
    0xa069, 0x0068, 0x406a, 0xe06b, 0xc06e, 0x606f, 0x206d, 0x806c,
    0x6067, 0xc066, 0x8064, 0x2065, 0x0060, 0xa061, 0xe063, 0x4062,
    0xc04e, 0x604f, 0x204d, 0x804c, 0xa049, 0x0048, 0x404a, 0xe04b,
    0x0040, 0xa041, 0xe043, 0x4042, 0x6047, 0xc046, 0x8044, 0x2045,
    0xe053, 0x4052, 0x0050, 0xa051, 0x8054, 0x2055, 0x6057, 0xc056,
    0x205d, 0x805c, 0xc05e, 0x605f, 0x405a, 0xe05b, 0xa059, 0x0058,
    0xa0e9, 0x00e8, 0x40ea, 0xe0eb, 0xc0ee, 0x60ef, 0x20ed, 0x80ec,
    0x60e7, 0xc0e6, 0x80e4, 0x20e5, 0x00e0, 0xa0e1, 0xe0e3, 0x40e2,
    0x80f4, 0x20f5, 0x60f7, 0xc0f6, 0xe0f3, 0x40f2, 0x00f0, 0xa0f1,
    0x40fa, 0xe0fb, 0xa0f9, 0x00f8, 0x20fd, 0x80fc, 0xc0fe, 0x60ff,
    0xe0d3, 0x40d2, 0x00d0, 0xa0d1, 0x80d4, 0x20d5, 0x60d7, 0xc0d6,
    0x20dd, 0x80dc, 0xc0de, 0x60df, 0x40da, 0xe0db, 0xa0d9, 0x00d8,
    0xc0ce, 0x60cf, 0x20cd, 0x80cc, 0xa0c9, 0x00c8, 0x40ca, 0xe0cb,
    0x00c0, 0xa0c1, 0xe0c3, 0x40c2, 0x60c7, 0xc0c6, 0x80c4, 0x20c5,
    0x209d, 0x809c, 0xc09e, 0x609f, 0x409a, 0xe09b, 0xa099, 0x0098,
    0xe093, 0x4092, 0x0090, 0xa091, 0x8094, 0x2095, 0x6097, 0xc096,
    0x0080, 0xa081, 0xe083, 0x4082, 0x6087, 0xc086, 0x8084, 0x2085,
    0xc08e, 0x608f, 0x208d, 0x808c, 0xa089, 0x0088, 0x408a, 0xe08b,
    0x60a7, 0xc0a6, 0x80a4, 0x20a5, 0x00a0, 0xa0a1, 0xe0a3, 0x40a2,
    0xa0a9, 0x00a8, 0x40aa, 0xe0ab, 0xc0ae, 0x60af, 0x20ad, 0x80ac,
    0x40ba, 0xe0bb, 0xa0b9, 0x00b8, 0x20bd, 0x80bc, 0xc0be, 0x60bf,
    0x80b4, 0x20b5, 0x60b7, 0xc0b6, 0xe0b3, 0x40b2, 0x00b0, 0xa0b1};

static unsigned char rev_table[] = {
    0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0,
    0x30, 0xb0, 0x70, 0xf0, 0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
    0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8, 0x04, 0x84, 0x44, 0xc4,
    0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
    0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc,
    0x3c, 0xbc, 0x7c, 0xfc, 0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
    0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2, 0x0a, 0x8a, 0x4a, 0xca,
    0x2a, 0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
    0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6,
    0x36, 0xb6, 0x76, 0xf6, 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
    0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe, 0x01, 0x81, 0x41, 0xc1,
    0x21, 0xa1, 0x61, 0xe1, 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
    0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19, 0x99, 0x59, 0xd9,
    0x39, 0xb9, 0x79, 0xf9, 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
    0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5, 0x0d, 0x8d, 0x4d, 0xcd,
    0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
    0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3,
    0x33, 0xb3, 0x73, 0xf3, 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
    0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb, 0x07, 0x87, 0x47, 0xc7,
    0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
    0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf,
    0x3f, 0xbf, 0x7f, 0xff};

unsigned crc16(unsigned crc, unsigned char *buf, int len)
{
    while (len--) {
        crc ^= *buf++ << 8;
        crc = (crc << 8) ^ crc16_table[(crc >> 8) & 0xff];
    }
    return crc & 0xffff;
}

inline unsigned rev16(unsigned val)
{
    return (rev_table[val & 0xff] << 8) | rev_table[(val >> 8) & 0xff];
}

这是哪种CRC算法？如何提高？

1 个答案: