求CRC算法的代码实现

yulihua49

回复  tanyayun 哈哈，我当年上计算机网络这门课的实验作业
jeung 发表于 2011-12-08 22:31

你这是在干啥呢？
ssh_crc32的生成多项式是：
    The polynomial used is 0xedb88320
在.h注释里有。

jeung

你这是在干啥呢？
ssh_crc32的生成多项式是：
    The polynomial used is 0xedb88320
在.h注释里有 ...
yulihua49 发表于 2011-12-09 17:07

    课本上给出了多种多项式，我省事就挑了个最短的= =
我那代码。。。唉，不知道诸位大神们有没有像我这样幼稚过

chinesedragon

这个算法不错

lmxcyx

头文件
#ifndef CRC32_H
#define CRC32_H

#include <QWidget>

class CRC32:public QWidget
{
        Q_OBJECT;
public:
        CRC32(QWidget *parent=0);
        virtual ~CRC32();
private:
        unsigned long m_Table[256];
        unsigned long Reflect(unsigned long ref,char ch);

public:
        void CRCInit(unsigned long &Result);
        void CRCUpdate(unsigned char* buffer,unsigned long size,unsigned long &Result);
        void CRCFinal(unsigned long &Result);
        QString ResultToHex(unsigned long Result,bool bUpper);
        QString GetCRC32Data(unsigned char *pData,unsigned long DataLen,bool bUpper);
};
#endif



源文件
#include "CRC32Ex.h"

CRC32::CRC32(QWidget *parent) : QWidget(parent)
{       
        unsigned long  ulPolynomial = 0x04C11DB7;
        for (int i = 0; i <= 0xFF; i++)
        {
                m_Table[i] = Reflect(i, << 24;
                for (int j = 0; j < 8; j++)
                        m_Table[i] = (m_Table[i] << 1) ^ (m_Table[i] & (1 << 31) ? ulPolynomial : 0);
                m_Table[i] = Reflect(m_Table[i], 32);
        }       
}

unsigned long CRC32::Reflect(unsigned long ref,char ch)
{
        unsigned long value = 0;
        for(int i = 1; i < (ch + 1); i++)
        {
                if (ref & 1)
                        value |= 1 << (ch - i);
                ref >>= 1;
        }
        return value;
}

void CRC32::CRCUpdate(unsigned char *buffer,unsigned long size,unsigned long &Result)
{
        while (size--)
                Result = (Result >> ^ m_Table[(Result & 0xFF) ^ *buffer++];
}

void CRC32::CRCInit(unsigned long &Result)
{
        Result=0xFFFFFFFF;
}

void CRC32::CRCFinal(unsigned long &Result)
{
        Result ^= 0xFFFFFFFF;
}

CRC32::~CRC32()
{

}

QString CRC32::ResultToHex(unsigned long Result,bool bUpper)
{
       
        QString S;
        if (bUpper)
                S.sprintf("%.8X",Result);
        else
                S.sprintf("%.8x",Result);
        return S;
}

QString CRC32::GetCRC32Data(unsigned char *pData,unsigned long DataLen,bool bUpper)
{
        unsigned long CRCResult;
        CRCInit(CRCResult);
        CRCUpdate(pData,DataLen,CRCResult);
        CRCFinal(CRCResult);
        return ResultToHex(CRCResult,bUpper);
}

yulihua49

头文件
#ifndef CRC32_H
#define CRC32_H

#include

class CRC32:public QWidget
{
        Q_OBJECT;
...
lmxcyx 发表于 2011-12-16 09:44

这是原生态的算法，大概不会比查表快。

c-aries

1. $ cat ~/source/linux/linux-2.6.36/arch/x86/boot/tools/build.c
   
2. /*
   
3. *  Copyright (C) 1991, 1992  Linus Torvalds
   
4. *  Copyright (C) 1997 Martin Mares
   
5. *  Copyright (C) 2007 H. Peter Anvin
   
6. */
   
7. 
   
8. /*
   
9. * This file builds a disk-image from two different files:
   
10. *
    
11. * - setup: 8086 machine code, sets up system parm
    
12. * - system: 80386 code for actual system
    
13. *
    
14. * It does some checking that all files are of the correct type, and
    
15. * just writes the result to stdout, removing headers and padding to
    
16. * the right amount. It also writes some system data to stderr.
    
17. */
    
18. 
    
19. /*
    
20. * Changes by tytso to allow root device specification
    
21. * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
    
22. * Cross compiling fixes by Gertjan van Wingerde, July 1996
    
23. * Rewritten by Martin Mares, April 1997
    
24. * Substantially overhauled by H. Peter Anvin, April 2007
    
25. */
    
26. 
    
27. #include <stdio.h>
    
28. #include <string.h>
    
29. #include <stdlib.h>
    
30. #include <stdarg.h>
    
31. #include <sys/types.h>
    
32. #include <sys/stat.h>
    
33. #include <sys/sysmacros.h>
    
34. #include <unistd.h>
    
35. #include <fcntl.h>
    
36. #include <sys/mman.h>
    
37. #include <asm/boot.h>
    
38. 
    
39. typedef unsigned char  u8;
    
40. typedef unsigned short u16;
    
41. typedef unsigned long  u32;
    
42. 
    
43. #define DEFAULT_MAJOR_ROOT 0
    
44. #define DEFAULT_MINOR_ROOT 0
    
45. 
    
46. /* Minimal number of setup sectors */
    
47. #define SETUP_SECT_MIN 5
    
48. #define SETUP_SECT_MAX 64
    
49. 
    
50. /* This must be large enough to hold the entire setup */
    
51. u8 buf[SETUP_SECT_MAX*512];
    
52. int is_big_kernel;
    
53. 
    
54. /*----------------------------------------------------------------------*/
    
55. 
    
56. static const u32 crctab32[] = {
    
57.         0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
    
58.         0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
    
59.         0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
    
60.         0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
    
61.         0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
    
62.         0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
    
63.         0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
    
64.         0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
    
65.         0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
    
66.         0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
    
67.         0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
    
68.         0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
    
69.         0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
    
70.         0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
    
71.         0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
    
72.         0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
    
73.         0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
    
74.         0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
    
75.         0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
    
76.         0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
    
77.         0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
    
78.         0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
    
79.         0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
    
80.         0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
    
81.         0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
    
82.         0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
    
83.         0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
    
84.         0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
    
85.         0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
    
86.         0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
    
87.         0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
    
88.         0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
    
89.         0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
    
90.         0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
    
91.         0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
    
92.         0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
    
93.         0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
    
94.         0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
    
95.         0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
    
96.         0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
    
97.         0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
    
98.         0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
    
99.         0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
    
100.         0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
     
101.         0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
     
102.         0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
     
103.         0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
     
104.         0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
     
105.         0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
     
106.         0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
     
107.         0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
     
108.         0x2d02ef8d
     
109. };
     
110. 
     
111. static u32 partial_crc32_one(u8 c, u32 crc)
     
112. {
     
113.         return crctab32[(crc ^ c) & 0xff] ^ (crc >> 8);
     
114. }
     
115. 
     
116. static u32 partial_crc32(const u8 *s, int len, u32 crc)
     
117. {
     
118.         while (len--)
     
119.                 crc = partial_crc32_one(*s++, crc);
     
120.         return crc;
     
121. }
     
122. 
     
123. static void die(const char * str, ...)
     
124. {
     
125.         va_list args;
     
126.         va_start(args, str);
     
127.         vfprintf(stderr, str, args);
     
128.         fputc('\n', stderr);
     
129.         exit(1);
     
130. }
     
131. 
     
132. static void usage(void)
     
133. {
     
134.         die("Usage: build setup system [rootdev] [> image]");
     
135. }
     
136. 
     
137. int main(int argc, char ** argv)
     
138. {
     
139.         unsigned int i, sz, setup_sectors;
     
140.         int c;
     
141.         u32 sys_size;
     
142.         u8 major_root, minor_root;
     
143.         struct stat sb;
     
144.         FILE *file;
     
145.         int fd;
     
146.         void *kernel;
     
147.         u32 crc = 0xffffffffUL;
     
148. 
     
149.         if ((argc < 3) || (argc > 4))
     
150.                 usage();
     
151.         if (argc > 3) {
     
152.                 if (!strcmp(argv[3], "CURRENT")) {
     
153.                         if (stat("/", &sb)) {
     
154.                                 perror("/");
     
155.                                 die("Couldn't stat /");
     
156.                         }
     
157.                         major_root = major(sb.st_dev);
     
158.                         minor_root = minor(sb.st_dev);
     
159.                 } else if (strcmp(argv[3], "FLOPPY")) {
     
160.                         if (stat(argv[3], &sb)) {
     
161.                                 perror(argv[3]);
     
162.                                 die("Couldn't stat root device.");
     
163.                         }
     
164.                         major_root = major(sb.st_rdev);
     
165.                         minor_root = minor(sb.st_rdev);
     
166.                 } else {
     
167.                         major_root = 0;
     
168.                         minor_root = 0;
     
169.                 }
     
170.         } else {
     
171.                 major_root = DEFAULT_MAJOR_ROOT;
     
172.                 minor_root = DEFAULT_MINOR_ROOT;
     
173.         }
     
174.         fprintf(stderr, "Root device is (%d, %d)\n", major_root, minor_root);
     
175. 
     
176.         /* Copy the setup code */
     
177.         file = fopen(argv[1], "r");
     
178.         if (!file)
     
179.                 die("Unable to open `%s': %m", argv[1]);
     
180.         c = fread(buf, 1, sizeof(buf), file);
     
181.         if (ferror(file))
     
182.                 die("read-error on `setup'");
     
183.         if (c < 1024)
     
184.                 die("The setup must be at least 1024 bytes");
     
185.         if (buf[510] != 0x55 || buf[511] != 0xaa)
     
186.                 die("Boot block hasn't got boot flag (0xAA55)");
     
187.         fclose(file);
     
188. 
     
189.         /* Pad unused space with zeros */
     
190.         setup_sectors = (c + 511) / 512;
     
191.         if (setup_sectors < SETUP_SECT_MIN)
     
192.                 setup_sectors = SETUP_SECT_MIN;
     
193.         i = setup_sectors*512;
     
194.         memset(buf+c, 0, i-c);
     
195. 
     
196.         /* Set the default root device */
     
197.         buf[508] = minor_root;
     
198.         buf[509] = major_root;
     
199. 
     
200.         fprintf(stderr, "Setup is %d bytes (padded to %d bytes).\n", c, i);
     
201. 
     
202.         /* Open and stat the kernel file */
     
203.         fd = open(argv[2], O_RDONLY);
     
204.         if (fd < 0)
     
205.                 die("Unable to open `%s': %m", argv[2]);
     
206.         if (fstat(fd, &sb))
     
207.                 die("Unable to stat `%s': %m", argv[2]);
     
208.         sz = sb.st_size;
     
209.         fprintf (stderr, "System is %d kB\n", (sz+1023)/1024);
     
210.         kernel = mmap(NULL, sz, PROT_READ, MAP_SHARED, fd, 0);
     
211.         if (kernel == MAP_FAILED)
     
212.                 die("Unable to mmap '%s': %m", argv[2]);
     
213.         /* Number of 16-byte paragraphs, including space for a 4-byte CRC */
     
214.         sys_size = (sz + 15 + 4) / 16;
     
215. 
     
216.         /* Patch the setup code with the appropriate size parameters */
     
217.         buf[0x1f1] = setup_sectors-1;
     
218.         buf[0x1f4] = sys_size;
     
219.         buf[0x1f5] = sys_size >> 8;
     
220.         buf[0x1f6] = sys_size >> 16;
     
221.         buf[0x1f7] = sys_size >> 24;
     
222. 
     
223.         crc = partial_crc32(buf, i, crc);
     
224.         if (fwrite(buf, 1, i, stdout) != i)
     
225.                 die("Writing setup failed");
     
226. 
     
227.         /* Copy the kernel code */
     
228.         crc = partial_crc32(kernel, sz, crc);
     
229.         if (fwrite(kernel, 1, sz, stdout) != sz)
     
230.                 die("Writing kernel failed");
     
231. 
     
232.         /* Add padding leaving 4 bytes for the checksum */
     
233.         while (sz++ < (sys_size*16) - 4) {
     
234.                 crc = partial_crc32_one('\0', crc);
     
235.                 if (fwrite("\0", 1, 1, stdout) != 1)
     
236.                         die("Writing padding failed");
     
237.         }
     
238. 
     
239.         /* Write the CRC */
     
240.         fprintf(stderr, "CRC %lx\n", crc);
     
241.         if (fwrite(&crc, 1, 4, stdout) != 4)
     
242.                 die("Writing CRC failed");
     
243. 
     
244.         close(fd);
     
245. 
     
246.         /* Everything is OK */
     
247.         return 0;
     
248. }
     
249. $
     

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