c++ - 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

这是一个说明问题的例子。由于我的计算机上没有 Linux 内核源代码，所以它稍长一些。如果您将 boost 链接到它，它就会编译。

问题是 Linux 和 boost 不同意 crc 值。Linux 源代码指出:

• 多项式... 0x8408。
• 加上隐含的 x^16，你就有了标准的 CRC-CCITT。

我不知道如何应用 x^16 但我死于编辑这个问题以反射(reflect)偏离的多项式。

#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;
}

我看到我没有为此说明我的用例。我有系统依赖性，需要使用不正确的(？)Linux crc。我想以一种允许我改为使用 boost 来执行此操作的方式来修剪 boost 实现。

我机器上的输出是:

Answer 1

更新 - 基于这些网站的 crc 计算器

(选择ccitt(0xffff)) http://www.lammertbies.nl/comm/info/crc-calculation.html

(选择crc ccitt) http://www.zorc.breitbandkatze.de/crc.html

第三个站点将此版本称为 crc-16-ccitt-false，并且还列出了其他也称为 ccitt 的变体。

http://reveng.sourceforge.net/crc-catalogue/16.htm#crc.cat.crc-16-ccitt-false

在这种情况下，位不会反转。此外，9 字节字符串“123456789”似乎是一个常见的测试。然而，其他网站提到某些版本的 ccitt 确实像在 linux 示例中所做的那样反转位。我的猜测是使用哪一个将是特定于协议(protocol)/设备的。如果您需要切换，至少现在您同时拥有反向 (linux) 和非反向(此答案中的代码)。

添加示例代码:

CRC 是将一串位除以 n 位多项式后的余数，产生 n-1 位余数。在软盘的情况下，17 位多项式 0x11021 用于产生 16 位余数。每个位的逻辑是这样的:

    crc << = 1;
    if(crc & 0x10000)crc ^= 0x11021;

这也可以实现:

    if(crc & 0x8000){crc = ((crc<<1) & 0xffff) & 0x1021;}
    else {crc = ((crc<<1) & 0xffff);}

示例代码。这应该与 boost 代码匹配。

typedef unsigned short u16;
typedef unsigned char u8;

u16 crctbl[256] = {
    0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,
    0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef,
    0x1231,0x0210,0x3273,0x2252,0x52b5,0x4294,0x72f7,0x62d6,
    0x9339,0x8318,0xb37b,0xa35a,0xd3bd,0xc39c,0xf3ff,0xe3de,
    0x2462,0x3443,0x0420,0x1401,0x64e6,0x74c7,0x44a4,0x5485,
    0xa56a,0xb54b,0x8528,0x9509,0xe5ee,0xf5cf,0xc5ac,0xd58d,
    0x3653,0x2672,0x1611,0x0630,0x76d7,0x66f6,0x5695,0x46b4,
    0xb75b,0xa77a,0x9719,0x8738,0xf7df,0xe7fe,0xd79d,0xc7bc,
    0x48c4,0x58e5,0x6886,0x78a7,0x0840,0x1861,0x2802,0x3823,
    0xc9cc,0xd9ed,0xe98e,0xf9af,0x8948,0x9969,0xa90a,0xb92b,
    0x5af5,0x4ad4,0x7ab7,0x6a96,0x1a71,0x0a50,0x3a33,0x2a12,
    0xdbfd,0xcbdc,0xfbbf,0xeb9e,0x9b79,0x8b58,0xbb3b,0xab1a,
    0x6ca6,0x7c87,0x4ce4,0x5cc5,0x2c22,0x3c03,0x0c60,0x1c41,
    0xedae,0xfd8f,0xcdec,0xddcd,0xad2a,0xbd0b,0x8d68,0x9d49,
    0x7e97,0x6eb6,0x5ed5,0x4ef4,0x3e13,0x2e32,0x1e51,0x0e70,
    0xff9f,0xefbe,0xdfdd,0xcffc,0xbf1b,0xaf3a,0x9f59,0x8f78,
    0x9188,0x81a9,0xb1ca,0xa1eb,0xd10c,0xc12d,0xf14e,0xe16f,
    0x1080,0x00a1,0x30c2,0x20e3,0x5004,0x4025,0x7046,0x6067,
    0x83b9,0x9398,0xa3fb,0xb3da,0xc33d,0xd31c,0xe37f,0xf35e,
    0x02b1,0x1290,0x22f3,0x32d2,0x4235,0x5214,0x6277,0x7256,
    0xb5ea,0xa5cb,0x95a8,0x8589,0xf56e,0xe54f,0xd52c,0xc50d,
    0x34e2,0x24c3,0x14a0,0x0481,0x7466,0x6447,0x5424,0x4405,
    0xa7db,0xb7fa,0x8799,0x97b8,0xe75f,0xf77e,0xc71d,0xd73c,
    0x26d3,0x36f2,0x0691,0x16b0,0x6657,0x7676,0x4615,0x5634,
    0xd94c,0xc96d,0xf90e,0xe92f,0x99c8,0x89e9,0xb98a,0xa9ab,
    0x5844,0x4865,0x7806,0x6827,0x18c0,0x08e1,0x3882,0x28a3,
    0xcb7d,0xdb5c,0xeb3f,0xfb1e,0x8bf9,0x9bd8,0xabbb,0xbb9a,
    0x4a75,0x5a54,0x6a37,0x7a16,0x0af1,0x1ad0,0x2ab3,0x3a92,
    0xfd2e,0xed0f,0xdd6c,0xcd4d,0xbdaa,0xad8b,0x9de8,0x8dc9,
    0x7c26,0x6c07,0x5c64,0x4c45,0x3ca2,0x2c83,0x1ce0,0x0cc1,
    0xef1f,0xff3e,0xcf5d,0xdf7c,0xaf9b,0xbfba,0x8fd9,0x9ff8,
    0x6e17,0x7e36,0x4e55,0x5e74,0x2e93,0x3eb2,0x0ed1,0x1ef0};

u16 gencrc(u8 *bfr, size_t len)
{
u16 crc = 0xffff;
    while(len--)
        crc = (crc << 8) ^ crctbl[(crc >> 8)^*bfr++];
    return(crc);
}

int main()
{
u16 crc;
u8 a[4]  = {0x80, 0, 0, 0};
u8 b[10] = {"123456789"};
    crc = gencrc(a, 1);   // returns 0x7078
    crc = gencrc(b, 9);   // returns 0x29b1
    return(0);
}