Boost CRC和linux/lib/crc-ccitt.c的区别

Question

我有两个来源来计算看似相同的crc值。我不明白为什么'boost/crc.hpp'实现与'linux/lib/crc-ccitt.c'实现不同。

CRC-CCITT.C boost

这里有一个例子说明了这个问题。因为我的电脑上没有Linux内核源码，所以这是一个很长的时间。如果将boost链接到它，它就会编译。

null

#include <stdio.h>
#include <boost\crc.hpp>

typedef unsigned short u16;
typedef unsigned char u8;

/*
*   linux/lib/crc-ccitt.c
*
*   This source code is licensed under the GNU General Public License,
*   Version 2. See the file COPYING for more details.
*/

/*modified for minimal example on stackoverflow*/
/*original source from http://mirrors.neusoft.edu.cn/rpi-kernel/lib/crc-ccitt.c */

u16 const crc_ccitt_table[256] = {
    0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
    0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
    0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
    0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
    0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
    0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
    0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
    0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
    0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
    0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
    0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
    0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
    0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
    0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
    0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
    0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
    0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
    0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
    0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
    0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
    0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
    0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
    0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
    0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
    0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
    0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
    0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
    0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
    0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
    0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
    0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
    0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};

//from crc-ccitt.h
static inline u16 crc_ccitt_byte(u16 crc, const u8 c)
{
    return (crc >> 8) ^ crc_ccitt_table[(crc ^ c) & 0xff];
}

u16 crc_ccitt(u16 crc, u8 const *buffer, size_t len)
{
    while (len--)
        crc = crc_ccitt_byte(crc, *buffer++);
    return crc;
}

#define check(X, Y) \
if (X != Y) { \
    printf("%s !=  %s\n", #X, #Y); \
} else { \
    printf("%s ==  %s   !!! celebrate\n", #X, #Y); \
} 

void runTestSet(unsigned char * data, unsigned size)
{
    u16 linux = crc_ccitt(0xFFFF, data, size);

    boost::crc_ccitt_type boost_crc_ccitt_type;
    boost::crc_16_type boost_crc_16_type;
    boost::crc_32_type boost_crc_32_type;
    boost::crc_xmodem_type boost_crc_xmodem_type;
    boost::crc_optimal<16, 0x8408, 0xFFFF, 0, false, false> boost_crc_optimal_16_8408_FFFF_0_0_0;
    boost::crc_optimal<16, 0x8408, 0xFFFF, 0, true, true> boost_crc_optimal_16_8408_FFFF_0_1_1;
    boost::crc_optimal<16, 0xA001, 0xFFFF, 0, true, true> boost_crc_optimal_16_A001_FFFF_0_1_1;
    boost::crc_optimal<16, 0x8408, 0xFFFF, 0, true, false> boost_crc_optimal_16_8408_FFFF_0_1_0;
    boost::crc_optimal<16, 0x856F, 0xFFFF, 0, true, true> boost_crc_optimal_16_856F_FFFF_0_1_1;
    boost::crc_optimal<16, 0x856F, 0xFFFF, 0, true, false> boost_crc_optimal_16_856F_FFFF_0_1_0;

    boost_crc_ccitt_type.process_bytes(data, size);
    boost_crc_16_type.process_bytes(data, size);
    boost_crc_32_type.process_bytes(data, size);
    boost_crc_xmodem_type.process_bytes(data, size);
    boost_crc_optimal_16_8408_FFFF_0_0_0.process_bytes(data, size);
    boost_crc_optimal_16_8408_FFFF_0_1_1.process_bytes(data, size);
    boost_crc_optimal_16_A001_FFFF_0_1_1.process_bytes(data, size);
    boost_crc_optimal_16_8408_FFFF_0_1_0.process_bytes(data, size);
    boost_crc_optimal_16_856F_FFFF_0_1_1.process_bytes(data, size);
    boost_crc_optimal_16_856F_FFFF_0_1_0.process_bytes(data, size);

    printf("Testing with sequence: '");
    for (unsigned n = 0; n < size; ++n)
    {
        if (n > 0) printf(" ");
        printf("0x%02X", data[n]);
    }
    printf("'\n");
    check(boost_crc_ccitt_type.checksum(), linux);
    check(boost_crc_16_type.checksum(), linux);
    check(boost_crc_32_type.checksum(), linux);
    check(boost_crc_xmodem_type.checksum(), linux);
    check(boost_crc_optimal_16_8408_FFFF_0_0_0.checksum(), linux);
    check(boost_crc_optimal_16_8408_FFFF_0_1_1.checksum(), linux);
    check(boost_crc_optimal_16_A001_FFFF_0_1_1.checksum(), linux);
    check(boost_crc_optimal_16_8408_FFFF_0_1_0.checksum(), linux);
    check(boost_crc_optimal_16_856F_FFFF_0_1_1.checksum(), linux);
    check(boost_crc_optimal_16_856F_FFFF_0_1_0.checksum(), linux);
    printf("End Of Testrun\n\n");
}


int main()
{
    unsigned char simple[] = {0x80};
    unsigned char sequence[] = "123456789";
    runTestSet(simple, sizeof(simple));
    runTestSet(sequence, sizeof(sequence));
    return 0;
}

我的机器上的输出是：

Answer 1

问题中的表格确实使用了多项式0x1021。可以通过使用以下简短程序生成表来检查这一点：

#include <iostream>

unsigned long SwapBits(unsigned long swap, int bits)
{
    unsigned long r = 0;
    for(int i = 0; i < bits; i++) {
        if(swap & 1) r |= 1 << (bits - i - 1);
        swap >>= 1;
    }
    return r;
}

int main()
{
    const unsigned short poly = 0x1021;
    unsigned short CRCTab[256];
    for(int i = 0; i < 256; i++) {
        CRCTab[i] = SwapBits(i, 8) << 8;
        for(int j = 0; j < 8; j++) CRCTab[i] = (CRCTab[i] << 1) ^ ((CRCTab[i] & 0x8000) ? poly : 0);
        CRCTab[i] = SwapBits(CRCTab[i], 16);
    }
    for(int i = 0; i < 256; ) {
        char str[10];
        for(int j = 0; j < 8; j++, i++) {
            sprintf(str, "0x%04x, ", CRCTab[i]);
            std::cout << str;
        }
        std::cout << "\n";
    }
    return 0;
}